No problem. Thanks. On Thu, Jul 11, 2024 at 10:59 AM Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > Great, thanks for testing them! Can we add a Tested-by: for you to the > patches? Consider posting your testcase as well. Maybe we can add it to > fstests or another testsuite. > > Thanks, > Jeff > > On Thu, 2024-07-11 at 10:54 -0400, Youzhong Yang wrote: > > I'd like to report that your patches + the "list_head nf_gc" patch > > together have been tested under heavy nfs load generated by machines > > in our testing farm, no leak has been observed. > > > > Surely my reproducer can no longer reproduce the issue once the > > patches are applied. > > > > FYI here is the reproducer: > > https://github.com/youzhongyang/nfsd-file-leaks > > > > On Wed, Jul 10, 2024 at 4:22 PM Jeff Layton <jlayton@xxxxxxxxxx> > > wrote: > > > > > > Great! If you're able to test the patches I sent earlier today, > > > please > > > let us know if they help with your reproducer. > > > > > > > > > On Wed, 2024-07-10 at 10:49 -0400, Youzhong Yang wrote: > > > > Thanks Jeff. Just sent out a separate e-mail. > > > > > > > > I have a simple reproducer now, it's a C program, I will upload > > > > it to > > > > a github repository together with a readme file and then post the > > > > link > > > > (if allowed) here. > > > > > > > > On Wed, Jul 10, 2024 at 9:40 AM Jeff Layton <jlayton@xxxxxxxxxx> > > > > wrote: > > > > > > > > > > Can you send it as a separate [PATCH] email? I think your MUA > > > > > is > > > > > mangling the patches as I couldn't apply it earlier. Either use > > > > > git- > > > > > send-email or have a look over this page: > > > > > > > > > > > > > > > > > > > > https://www.kernel.org/doc/html/latest/process/email-clients.html#email-clients > > > > > > > > > > Thanks! > > > > > Jeff > > > > > > > > > > On Wed, 2024-07-10 at 09:33 -0400, Youzhong Yang wrote: > > > > > > Thanks. Here it is again: > > > > > > > > > > > > commit c6e69cebc052cb82d91fc81a98aee20749fe8d47 > > > > > > Author: Youzhong Yang <youzhong@xxxxxxxxx> > > > > > > Date: Thu Jul 4 11:25:40 2024 -0400 > > > > > > > > > > > > nfsd: fix nfsd_file leaking due to mixed use of nf- > > > > > > >nf_lru > > > > > > > > > > > > nfsd_file_put() in one thread can race with another > > > > > > thread doing > > > > > > garbage collection (running nfsd_file_gc() -> > > > > > > list_lru_walk() -> > > > > > > nfsd_file_lru_cb()): > > > > > > > > > > > > * In nfsd_file_put(), nf->nf_ref is 1, so it tries to > > > > > > do > > > > > > nfsd_file_lru_add(). > > > > > > * nfsd_file_lru_add() returns true (with > > > > > > NFSD_FILE_REFERENCED > > > > > > bit set) > > > > > > * garbage collector kicks in, nfsd_file_lru_cb() clears > > > > > > REFERENCED bit and > > > > > > returns LRU_ROTATE. > > > > > > * garbage collector kicks in again, nfsd_file_lru_cb() > > > > > > now > > > > > > decrements nf->nf_ref > > > > > > to 0, runs nfsd_file_unhash(), removes it from the > > > > > > LRU and > > > > > > adds to the dispose > > > > > > list [list_lru_isolate_move(lru, &nf->nf_lru, head)] > > > > > > * nfsd_file_put() detects NFSD_FILE_HASHED bit is > > > > > > cleared, so > > > > > > it > > > > > > tries to remove > > > > > > the 'nf' from the LRU [if > > > > > > (!nfsd_file_lru_remove(nf))]. The > > > > > > 'nf' has been added > > > > > > to the 'dispose' list by nfsd_file_lru_cb(), so > > > > > > nfsd_file_lru_remove(nf) simply > > > > > > treats it as part of the LRU and removes it, which > > > > > > leads to > > > > > > its removal from > > > > > > the 'dispose' list. > > > > > > * At this moment, 'nf' is unhashed with its nf_ref > > > > > > being 0, and > > > > > > not on the LRU. > > > > > > nfsd_file_put() continues its execution [if > > > > > > (refcount_dec_and_test(&nf->nf_ref))], > > > > > > as nf->nf_ref is already 0, nf->nf_ref is set to > > > > > > REFCOUNT_SATURATED, and the 'nf' > > > > > > gets no chance of being freed. > > > > > > > > > > > > nfsd_file_put() can also race with > > > > > > nfsd_file_cond_queue(): > > > > > > * In nfsd_file_put(), nf->nf_ref is 1, so it tries to > > > > > > do > > > > > > nfsd_file_lru_add(). > > > > > > * nfsd_file_lru_add() sets REFERENCED bit and returns > > > > > > true. > > > > > > * Some userland application runs 'exportfs -f' or > > > > > > something > > > > > > like > > > > > > that, which triggers > > > > > > __nfsd_file_cache_purge() -> nfsd_file_cond_queue(). > > > > > > * In nfsd_file_cond_queue(), it runs [if > > > > > > (!nfsd_file_unhash(nf))], unhash is done > > > > > > successfully. > > > > > > * nfsd_file_cond_queue() runs [if > > > > > > (!nfsd_file_get(nf))], now > > > > > > nf->nf_ref goes to 2. > > > > > > * nfsd_file_cond_queue() runs [if > > > > > > (nfsd_file_lru_remove(nf))], > > > > > > it succeeds. > > > > > > * nfsd_file_cond_queue() runs [if > > > > > > (refcount_sub_and_test(decrement, &nf->nf_ref))] > > > > > > (with "decrement" being 2), so the nf->nf_ref goes to > > > > > > 0, the > > > > > > 'nf' is added to the > > > > > > dispose list [list_add(&nf->nf_lru, dispose)] > > > > > > * nfsd_file_put() detects NFSD_FILE_HASHED bit is > > > > > > cleared, so > > > > > > it > > > > > > tries to remove > > > > > > the 'nf' from the LRU [if > > > > > > (!nfsd_file_lru_remove(nf))], > > > > > > although the 'nf' is not > > > > > > in the LRU, but it is linked in the 'dispose' list, > > > > > > nfsd_file_lru_remove() simply > > > > > > treats it as part of the LRU and removes it. This > > > > > > leads to > > > > > > its > > > > > > removal from > > > > > > the 'dispose' list! > > > > > > * Now nf->ref is 0, unhashed. nfsd_file_put() continues > > > > > > its > > > > > > execution and set > > > > > > nf->nf_ref to REFCOUNT_SATURATED. > > > > > > > > > > > > As shown in the above analysis, using nf_lru for both the > > > > > > LRU > > > > > > list > > > > > > and dispose list > > > > > > can cause the leaks. This patch adds a new list_head > > > > > > nf_gc in > > > > > > struct nfsd_file, and uses > > > > > > it for the dispose list. > > > > > > > > > > > > Signed-off-by: Youzhong Yang <youzhong@xxxxxxxxx> > > > > > > > > > > > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > > > > > > index ad9083ca144b..22ebd7fb8639 100644 > > > > > > --- a/fs/nfsd/filecache.c > > > > > > +++ b/fs/nfsd/filecache.c > > > > > > @@ -216,6 +216,7 @@ nfsd_file_alloc(struct net *net, struct > > > > > > inode > > > > > > *inode, unsigned char need, > > > > > > return NULL; > > > > > > > > > > > > INIT_LIST_HEAD(&nf->nf_lru); > > > > > > + INIT_LIST_HEAD(&nf->nf_gc); > > > > > > nf->nf_birthtime = ktime_get(); > > > > > > nf->nf_file = NULL; > > > > > > nf->nf_cred = get_current_cred(); > > > > > > @@ -393,8 +394,8 @@ nfsd_file_dispose_list(struct list_head > > > > > > *dispose) > > > > > > struct nfsd_file *nf; > > > > > > > > > > > > while (!list_empty(dispose)) { > > > > > > - nf = list_first_entry(dispose, struct > > > > > > nfsd_file, > > > > > > nf_lru); > > > > > > - list_del_init(&nf->nf_lru); > > > > > > + nf = list_first_entry(dispose, struct > > > > > > nfsd_file, > > > > > > nf_gc); > > > > > > + list_del_init(&nf->nf_gc); > > > > > > nfsd_file_free(nf); > > > > > > } > > > > > > } > > > > > > @@ -411,12 +412,12 @@ nfsd_file_dispose_list_delayed(struct > > > > > > list_head > > > > > > *dispose) > > > > > > { > > > > > > while(!list_empty(dispose)) { > > > > > > struct nfsd_file *nf = > > > > > > list_first_entry(dispose, > > > > > > - struct > > > > > > nfsd_file, > > > > > > nf_lru); > > > > > > + struct > > > > > > nfsd_file, > > > > > > nf_gc); > > > > > > struct nfsd_net *nn = net_generic(nf->nf_net, > > > > > > nfsd_net_id); > > > > > > struct nfsd_fcache_disposal *l = nn- > > > > > > >fcache_disposal; > > > > > > > > > > > > spin_lock(&l->lock); > > > > > > - list_move_tail(&nf->nf_lru, &l->freeme); > > > > > > + list_move_tail(&nf->nf_gc, &l->freeme); > > > > > > spin_unlock(&l->lock); > > > > > > svc_wake_up(nn->nfsd_serv); > > > > > > } > > > > > > @@ -503,7 +504,8 @@ nfsd_file_lru_cb(struct list_head *item, > > > > > > struct > > > > > > list_lru_one *lru, > > > > > > > > > > > > /* Refcount went to zero. Unhash it and queue it to > > > > > > the > > > > > > dispose list */ > > > > > > nfsd_file_unhash(nf); > > > > > > - list_lru_isolate_move(lru, &nf->nf_lru, head); > > > > > > + list_lru_isolate(lru, &nf->nf_lru); > > > > > > + list_add(&nf->nf_gc, head); > > > > > > this_cpu_inc(nfsd_file_evictions); > > > > > > trace_nfsd_file_gc_disposed(nf); > > > > > > return LRU_REMOVED; > > > > > > @@ -578,7 +580,7 @@ nfsd_file_cond_queue(struct nfsd_file > > > > > > *nf, struct > > > > > > list_head *dispose) > > > > > > > > > > > > /* If refcount goes to 0, then put on the dispose > > > > > > list */ > > > > > > if (refcount_sub_and_test(decrement, &nf->nf_ref)) { > > > > > > - list_add(&nf->nf_lru, dispose); > > > > > > + list_add(&nf->nf_gc, dispose); > > > > > > trace_nfsd_file_closing(nf); > > > > > > } > > > > > > } > > > > > > @@ -654,8 +656,8 @@ nfsd_file_close_inode_sync(struct inode > > > > > > *inode) > > > > > > > > > > > > nfsd_file_queue_for_close(inode, &dispose); > > > > > > while (!list_empty(&dispose)) { > > > > > > - nf = list_first_entry(&dispose, struct > > > > > > nfsd_file, > > > > > > nf_lru); > > > > > > - list_del_init(&nf->nf_lru); > > > > > > + nf = list_first_entry(&dispose, struct > > > > > > nfsd_file, > > > > > > nf_gc); > > > > > > + list_del_init(&nf->nf_gc); > > > > > > nfsd_file_free(nf); > > > > > > } > > > > > > } > > > > > > diff --git a/fs/nfsd/filecache.h b/fs/nfsd/filecache.h > > > > > > index c61884def906..3fbec24eea6c 100644 > > > > > > --- a/fs/nfsd/filecache.h > > > > > > +++ b/fs/nfsd/filecache.h > > > > > > @@ -44,6 +44,7 @@ struct nfsd_file { > > > > > > > > > > > > struct nfsd_file_mark *nf_mark; > > > > > > struct list_head nf_lru; > > > > > > + struct list_head nf_gc; > > > > > > struct rcu_head nf_rcu; > > > > > > ktime_t nf_birthtime; > > > > > > }; > > > > > > > > > > > > On Wed, Jul 10, 2024 at 8:49 AM Jeff Layton > > > > > > <jlayton@xxxxxxxxxx> > > > > > > wrote: > > > > > > > > > > > > > > Ok, thanks. I went crawling over the filecache code, and > > > > > > > found a > > > > > > > couple > > > > > > > of potential nfsd_file leaks. I'm testing patches now and > > > > > > > will > > > > > > > likely > > > > > > > send them along later today. > > > > > > > > > > > > > > I think we do still want the patch to add nf_gc list_head. > > > > > > > I'm not > > > > > > > certain there is a race there, but it's safer to just use a > > > > > > > separate > > > > > > > list_head and it doesn't represent a lot of memory. > > > > > > > > > > > > > > Could you post that one individually so that Chuck can pick > > > > > > > it up? > > > > > > > > > > > > > > Thanks, > > > > > > > Jeff > > > > > > > > > > > > > > On Tue, 2024-07-09 at 15:13 -0400, Youzhong Yang wrote: > > > > > > > > It's not on the LRU: > > > > > > > > > > > > > > > > crash> struct > > > > > > > > nfsd_file.nf_flags,nf_ref.refs.counter,nf_lru,nf_gc > > > > > > > > ffff898107b95980 > > > > > > > > nf_flags = 12, > > > > > > > > nf_ref.refs.counter = 1 > > > > > > > > nf_lru = { > > > > > > > > next = 0xffff898107b959c8, > > > > > > > > prev = 0xffff898107b959c8 > > > > > > > > }, > > > > > > > > nf_gc = { > > > > > > > > next = 0xffff898107b959d8, > > > > > > > > prev = 0xffff898107b959d8 > > > > > > > > }, > > > > > > > > > > > > > > > > I don't have an easy reproducer now as I am having > > > > > > > > difficulty > > > > > > > > generating tons of NFS read/write ops using a limited > > > > > > > > number of > > > > > > > > nfs > > > > > > > > clients. I use our in-house testing farm to test the > > > > > > > > patch. > > > > > > > > > > > > > > > > Thanks. > > > > > > > > > > > > > > > > On Tue, Jul 9, 2024 at 3:05 PM Jeff Layton > > > > > > > > <jlayton@xxxxxxxxxx> > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > On Tue, 2024-07-09 at 14:37 -0400, Youzhong Yang wrote: > > > > > > > > > > Thanks Jeff. > > > > > > > > > > > > > > > > > > > > Unfortunately the early unhash easily leads to leaks: > > > > > > > > > > > > > > > > > > > > crash> kmem -S nfsd_file | grep '\[ffff' | sed -e > > > > > > > > > > 's|\[||' -e > > > > > > > > > > 's|\]||' > > > > > > > > > > > xargs -i echo struct > > > > > > > > > > > nfsd_file.nf_flags,nf_ref.refs.counter > > > > > > > > > > > '{}' > > > > > > > > > > > /var/tmp/nfsd_files > > > > > > > > > > crash> !wc -l /var/tmp/nfsd_files > > > > > > > > > > 19 /var/tmp/nfsd_files > > > > > > > > > > crash> < /var/tmp/nfsd_files > > > > > > > > > > crash> struct nfsd_file.nf_flags,nf_ref.refs.counter > > > > > > > > > > ffff88865c778900 > > > > > > > > > > nf_flags = 8, > > > > > > > > > > nf_ref.refs.counter = 2 > > > > > > > > > > crash> struct nfsd_file.nf_flags,nf_ref.refs.counter > > > > > > > > > > ffff88865c778cc0 > > > > > > > > > > nf_flags = 8, > > > > > > > > > > nf_ref.refs.counter = 3 > > > > > > > > > > crash> struct nfsd_file.nf_flags,nf_ref.refs.counter > > > > > > > > > > ffff8885d5f35e00 > > > > > > > > > > nf_flags = 8, > > > > > > > > > > nf_ref.refs.counter = 1 > > > > > > > > > > crash> struct nfsd_file.nf_flags,nf_ref.refs.counter > > > > > > > > > > ffff88817443e780 > > > > > > > > > > nf_flags = 8, > > > > > > > > > > nf_ref.refs.counter = 3 > > > > > > > > > > crash> struct nfsd_file.nf_flags,nf_ref.refs.counter > > > > > > > > > > ffff88818b3f0600 > > > > > > > > > > nf_flags = 8, > > > > > > > > > > nf_ref.refs.counter = 2 > > > > > > > > > > crash> struct nfsd_file.nf_flags,nf_ref.refs.counter > > > > > > > > > > ffff88a4490f8300 > > > > > > > > > > nf_flags = 8, > > > > > > > > > > nf_ref.refs.counter = 1 > > > > > > > > > > crash> struct nfsd_file.nf_flags,nf_ref.refs.counter > > > > > > > > > > ffff88a0dab183c0 > > > > > > > > > > nf_flags = 8, > > > > > > > > > > nf_ref.refs.counter = 40 > > > > > > > > > > > > > > > > > > That's a lot of references! Might be interesting to > > > > > > > > > look more > > > > > > > > > closely > > > > > > > > > at that one, but the refcounts are all over the place, > > > > > > > > > so it > > > > > > > > > really > > > > > > > > > does look like we just have a refcount leak somewhere. > > > > > > > > > > > > > > > > > > > ... > > > > > > > > > > crash> struct nfsd_file.nf_flags,nf_ref.refs.counter > > > > > > > > > > ffff89209535f200 > > > > > > > > > > nf_flags = 8, > > > > > > > > > > nf_ref.refs.counter = 2 > > > > > > > > > > crash> struct nfsd_file.nf_flags,nf_ref.refs.counter > > > > > > > > > > ffff8980e15138c0 > > > > > > > > > > nf_flags = 8, > > > > > > > > > > nf_ref.refs.counter = 7 > > > > > > > > > > crash> struct nfsd_file.nf_flags,nf_ref.refs.counter > > > > > > > > > > ffff898107b95800 > > > > > > > > > > nf_flags = 8, > > > > > > > > > > nf_ref.refs.counter = 3 > > > > > > > > > > crash> struct nfsd_file.nf_flags,nf_ref.refs.counter > > > > > > > > > > ffff898107b95980 > > > > > > > > > > nf_flags = 12, > > > > > > > > > > > > > > > > > > The others are NFSD_FILE_GC. This one is also > > > > > > > > > NFSD_FILE_REFERENCED. Are > > > > > > > > > these objects on the LRU? > > > > > > > > > > > > > > > > > > > nf_ref.refs.counter = 1 > > > > > > > > > > > > > > > > > > > > nfsd_file_do_acquire() -> nfsd_file_lookup_locked() > > > > > > > > > > relies on > > > > > > > > > > the > > > > > > > > > > hash > > > > > > > > > > table to find the nfsd_file, > > > > > > > > > > but I am still scratching my head why and how this > > > > > > > > > > happens. > > > > > > > > > > > > > > > > > > > > FYI, here is the patch I applied for testing: > > > > > > > > > > > > > > > > > > > > > > > > > > > > The above suggests to me that there is a garden-variety > > > > > > > > > refcount leak > > > > > > > > > somewhere. Whenever some bit of the code takes a > > > > > > > > > reference to > > > > > > > > > an object > > > > > > > > > (like a nfsd_file), it's implicitly required to > > > > > > > > > eventually put > > > > > > > > > that > > > > > > > > > reference. Typically that means that the code needs to > > > > > > > > > maintain > > > > > > > > > a > > > > > > > > > pointer to that object, as it can be unhashed at any > > > > > > > > > time and > > > > > > > > > it can't > > > > > > > > > rely on finding the same object later. > > > > > > > > > > > > > > > > > > Do you have a reproducer for this? > > > > > > > > > > > > > > > > > > > diff --git a/fs/nfsd/filecache.c > > > > > > > > > > b/fs/nfsd/filecache.c > > > > > > > > > > index ad9083ca144b..22ebd7fb8639 100644 > > > > > > > > > > --- a/fs/nfsd/filecache.c > > > > > > > > > > +++ b/fs/nfsd/filecache.c > > > > > > > > > > @@ -216,6 +216,7 @@ nfsd_file_alloc(struct net *net, > > > > > > > > > > struct > > > > > > > > > > inode > > > > > > > > > > *inode, unsigned char need, > > > > > > > > > > return NULL; > > > > > > > > > > > > > > > > > > > > INIT_LIST_HEAD(&nf->nf_lru); > > > > > > > > > > + INIT_LIST_HEAD(&nf->nf_gc); > > > > > > > > > > nf->nf_birthtime = ktime_get(); > > > > > > > > > > nf->nf_file = NULL; > > > > > > > > > > nf->nf_cred = get_current_cred(); > > > > > > > > > > @@ -393,8 +394,8 @@ nfsd_file_dispose_list(struct > > > > > > > > > > list_head > > > > > > > > > > *dispose) > > > > > > > > > > struct nfsd_file *nf; > > > > > > > > > > > > > > > > > > > > while (!list_empty(dispose)) { > > > > > > > > > > - nf = list_first_entry(dispose, struct > > > > > > > > > > nfsd_file, > > > > > > > > > > nf_lru); > > > > > > > > > > - list_del_init(&nf->nf_lru); > > > > > > > > > > + nf = list_first_entry(dispose, struct > > > > > > > > > > nfsd_file, > > > > > > > > > > nf_gc); > > > > > > > > > > + list_del_init(&nf->nf_gc); > > > > > > > > > > nfsd_file_free(nf); > > > > > > > > > > } > > > > > > > > > > } > > > > > > > > > > @@ -411,12 +412,12 @@ > > > > > > > > > > nfsd_file_dispose_list_delayed(struct > > > > > > > > > > list_head > > > > > > > > > > *dispose) > > > > > > > > > > { > > > > > > > > > > while(!list_empty(dispose)) { > > > > > > > > > > struct nfsd_file *nf = > > > > > > > > > > list_first_entry(dispose, > > > > > > > > > > - > > > > > > > > > > struct > > > > > > > > > > nfsd_file, > > > > > > > > > > nf_lru); > > > > > > > > > > + > > > > > > > > > > struct > > > > > > > > > > nfsd_file, > > > > > > > > > > nf_gc); > > > > > > > > > > struct nfsd_net *nn = net_generic(nf- > > > > > > > > > > >nf_net, > > > > > > > > > > nfsd_net_id); > > > > > > > > > > struct nfsd_fcache_disposal *l = nn- > > > > > > > > > > > fcache_disposal; > > > > > > > > > > > > > > > > > > > > spin_lock(&l->lock); > > > > > > > > > > - list_move_tail(&nf->nf_lru, &l- > > > > > > > > > > >freeme); > > > > > > > > > > + list_move_tail(&nf->nf_gc, &l- > > > > > > > > > > >freeme); > > > > > > > > > > spin_unlock(&l->lock); > > > > > > > > > > svc_wake_up(nn->nfsd_serv); > > > > > > > > > > } > > > > > > > > > > @@ -503,7 +504,8 @@ nfsd_file_lru_cb(struct list_head > > > > > > > > > > *item, > > > > > > > > > > struct > > > > > > > > > > list_lru_one *lru, > > > > > > > > > > > > > > > > > > > > /* Refcount went to zero. Unhash it and queue > > > > > > > > > > it to > > > > > > > > > > the > > > > > > > > > > dispose list */ > > > > > > > > > > nfsd_file_unhash(nf); > > > > > > > > > > - list_lru_isolate_move(lru, &nf->nf_lru, > > > > > > > > > > head); > > > > > > > > > > + list_lru_isolate(lru, &nf->nf_lru); > > > > > > > > > > + list_add(&nf->nf_gc, head); > > > > > > > > > > this_cpu_inc(nfsd_file_evictions); > > > > > > > > > > trace_nfsd_file_gc_disposed(nf); > > > > > > > > > > return LRU_REMOVED; > > > > > > > > > > @@ -578,7 +580,7 @@ nfsd_file_cond_queue(struct > > > > > > > > > > nfsd_file > > > > > > > > > > *nf, struct > > > > > > > > > > list_head *dispose) > > > > > > > > > > > > > > > > > > > > /* If refcount goes to 0, then put on the > > > > > > > > > > dispose > > > > > > > > > > list */ > > > > > > > > > > if (refcount_sub_and_test(decrement, &nf- > > > > > > > > > > >nf_ref)) { > > > > > > > > > > - list_add(&nf->nf_lru, dispose); > > > > > > > > > > + list_add(&nf->nf_gc, dispose); > > > > > > > > > > trace_nfsd_file_closing(nf); > > > > > > > > > > } > > > > > > > > > > } > > > > > > > > > > @@ -654,8 +656,8 @@ nfsd_file_close_inode_sync(struct > > > > > > > > > > inode > > > > > > > > > > *inode) > > > > > > > > > > > > > > > > > > > > nfsd_file_queue_for_close(inode, &dispose); > > > > > > > > > > while (!list_empty(&dispose)) { > > > > > > > > > > - nf = list_first_entry(&dispose, > > > > > > > > > > struct > > > > > > > > > > nfsd_file, > > > > > > > > > > nf_lru); > > > > > > > > > > - list_del_init(&nf->nf_lru); > > > > > > > > > > + nf = list_first_entry(&dispose, > > > > > > > > > > struct > > > > > > > > > > nfsd_file, > > > > > > > > > > nf_gc); > > > > > > > > > > + list_del_init(&nf->nf_gc); > > > > > > > > > > nfsd_file_free(nf); > > > > > > > > > > } > > > > > > > > > > } > > > > > > > > > > diff --git a/fs/nfsd/filecache.h > > > > > > > > > > b/fs/nfsd/filecache.h > > > > > > > > > > index c61884def906..3fbec24eea6c 100644 > > > > > > > > > > --- a/fs/nfsd/filecache.h > > > > > > > > > > +++ b/fs/nfsd/filecache.h > > > > > > > > > > @@ -44,6 +44,7 @@ struct nfsd_file { > > > > > > > > > > > > > > > > > > > > struct nfsd_file_mark *nf_mark; > > > > > > > > > > struct list_head nf_lru; > > > > > > > > > > + struct list_head nf_gc; > > > > > > > > > > struct rcu_head nf_rcu; > > > > > > > > > > ktime_t nf_birthtime; > > > > > > > > > > }; > > > > > > > > > > > > > > > > > > > > On Mon, Jul 8, 2024 at 10:55 AM Jeff Layton > > > > > > > > > > <jlayton@xxxxxxxxxx> > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > On Mon, 2024-07-08 at 10:23 -0400, Youzhong Yang > > > > > > > > > > > wrote: > > > > > > > > > > > > Thanks Jeff. > > > > > > > > > > > > > > > > > > > > > > > > I am ok with reverting the unhash/dispose list > > > > > > > > > > > > reordering > > > > > > > > > > > > in > > > > > > > > > > > > nfsd_file_lru_cb(), as it doesn't make much of a > > > > > > > > > > > > difference, > > > > > > > > > > > > but for nfsd_file_cond_queue(), imagining this: > > > > > > > > > > > > > > > > > > > > > > > > - A nfsd_file is hashed > > > > > > > > > > > > - In nfsd_file_cond_queue(), [if > > > > > > > > > > > > (!nfsd_file_unhash(nf))] > > > > > > > > > > > > will > > > > > > > > > > > > get it > > > > > > > > > > > > unhashed, doesn't it? > > > > > > > > > > > > - It continues to get a reference by > > > > > > > > > > > > nfsd_file_get() > > > > > > > > > > > > - It continues to remove itself from LRU by > > > > > > > > > > > > nfsd_file_lru_remove() if > > > > > > > > > > > > it is on the LRU. > > > > > > > > > > > > - Now it runs refcount_sub_and_test(), what > > > > > > > > > > > > happens if > > > > > > > > > > > > the refcnt > > > > > > > > > > > > does > > > > > > > > > > > > not go to 0? How can this nfsd_file be found > > > > > > > > > > > > again? > > > > > > > > > > > > Through the > > > > > > > > > > > > hash > > > > > > > > > > > > table? Through the LRU walk? how? > > > > > > > > > > > > > > > > > > > > > > > > Thanks again. > > > > > > > > > > > > > > > > > > > > > > > > -Youzhong > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > It won't need to be found again. The holders of the > > > > > > > > > > > extra > > > > > > > > > > > references > > > > > > > > > > > will put those references when they are finished. > > > > > > > > > > > Since the > > > > > > > > > > > object > > > > > > > > > > > is > > > > > > > > > > > no longer HASHED, nfsd_file_put just does this: > > > > > > > > > > > > > > > > > > > > > > if (refcount_dec_and_test(&nf->nf_ref)) > > > > > > > > > > > nfsd_file_free(nf); > > > > > > > > > > > > > > > > > > > > > > So that should be fine. > > > > > > > > > > > > > > > > > > > > > > > On Mon, Jul 8, 2024 at 9:35 AM Jeff Layton > > > > > > > > > > > > <jlayton@xxxxxxxxxx> > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > On Mon, 2024-07-08 at 08:58 -0400, Youzhong > > > > > > > > > > > > > Yang wrote: > > > > > > > > > > > > > > Thank you Jeff for your invaluable insights. > > > > > > > > > > > > > > I was > > > > > > > > > > > > > > leaning > > > > > > > > > > > > > > towards > > > > > > > > > > > > > > adding a new list_head too, and tested this > > > > > > > > > > > > > > approach > > > > > > > > > > > > > > on > > > > > > > > > > > > > > kernel > > > > > > > > > > > > > > 6.6 by > > > > > > > > > > > > > > continuously hammering the server with heavy > > > > > > > > > > > > > > nfs load > > > > > > > > > > > > > > for the > > > > > > > > > > > > > > last few > > > > > > > > > > > > > > days, not a single leak. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Here goes the patch (based on Linux kernel > > > > > > > > > > > > > > master > > > > > > > > > > > > > > branch), > > > > > > > > > > > > > > please > > > > > > > > > > > > > > review: > > > > > > > > > > > > > > > > > > > > > > > > > > > > From: Youzhong Yang <youzhong@xxxxxxxxx> > > > > > > > > > > > > > > Date: Thu, 4 Jul 2024 11:25:40 -0400 > > > > > > > > > > > > > > Subject: [PATCH] nfsd: fix nfsd_file leaking > > > > > > > > > > > > > > due to > > > > > > > > > > > > > > mixed use > > > > > > > > > > > > > > of > > > > > > > > > > > > > > nf->nf_lru > > > > > > > > > > > > > > > > > > > > > > > > > > > > nfsd_file_put() in one thread can race with > > > > > > > > > > > > > > another > > > > > > > > > > > > > > thread > > > > > > > > > > > > > > doing > > > > > > > > > > > > > > garbage collection (running nfsd_file_gc() -> > > > > > > > > > > > > > > list_lru_walk() > > > > > > > > > > > > > > -> > > > > > > > > > > > > > > nfsd_file_lru_cb()): > > > > > > > > > > > > > > > > > > > > > > > > > > > > * In nfsd_file_put(), nf->nf_ref is 1, so > > > > > > > > > > > > > > it tries > > > > > > > > > > > > > > to do > > > > > > > > > > > > > > nfsd_file_lru_add(). > > > > > > > > > > > > > > * nfsd_file_lru_add() returns true (with > > > > > > > > > > > > > > NFSD_FILE_REFERENCED > > > > > > > > > > > > > > bit set) > > > > > > > > > > > > > > * garbage collector kicks in, > > > > > > > > > > > > > > nfsd_file_lru_cb() > > > > > > > > > > > > > > clears > > > > > > > > > > > > > > REFERENCED bit and > > > > > > > > > > > > > > returns LRU_ROTATE. > > > > > > > > > > > > > > * garbage collector kicks in again, > > > > > > > > > > > > > > nfsd_file_lru_cb() now > > > > > > > > > > > > > > decrements nf->nf_ref > > > > > > > > > > > > > > to 0, runs nfsd_file_unhash(), removes it > > > > > > > > > > > > > > from > > > > > > > > > > > > > > the LRU > > > > > > > > > > > > > > and > > > > > > > > > > > > > > adds to > > > > > > > > > > > > > > the dispose > > > > > > > > > > > > > > list [list_lru_isolate_move(lru, &nf- > > > > > > > > > > > > > > >nf_lru, > > > > > > > > > > > > > > head)] > > > > > > > > > > > > > > * nfsd_file_put() detects NFSD_FILE_HASHED > > > > > > > > > > > > > > bit is > > > > > > > > > > > > > > cleared, > > > > > > > > > > > > > > so > > > > > > > > > > > > > > it > > > > > > > > > > > > > > tries to remove > > > > > > > > > > > > > > the 'nf' from the LRU [if > > > > > > > > > > > > > > (!nfsd_file_lru_remove(nf))]. > > > > > > > > > > > > > > The > > > > > > > > > > > > > > 'nf' > > > > > > > > > > > > > > has been added > > > > > > > > > > > > > > to the 'dispose' list by > > > > > > > > > > > > > > nfsd_file_lru_cb(), so > > > > > > > > > > > > > > nfsd_file_lru_remove(nf) simply > > > > > > > > > > > > > > treats it as part of the LRU and removes > > > > > > > > > > > > > > it, > > > > > > > > > > > > > > which leads > > > > > > > > > > > > > > to > > > > > > > > > > > > > > its removal from > > > > > > > > > > > > > > the 'dispose' list. > > > > > > > > > > > > > > * At this moment, 'nf' is unhashed with its > > > > > > > > > > > > > > nf_ref > > > > > > > > > > > > > > being 0, > > > > > > > > > > > > > > and > > > > > > > > > > > > > > not > > > > > > > > > > > > > > on the LRU. > > > > > > > > > > > > > > nfsd_file_put() continues its execution > > > > > > > > > > > > > > [if > > > > > > > > > > > > > > (refcount_dec_and_test(&nf->nf_ref))], > > > > > > > > > > > > > > as nf->nf_ref is already 0, nf->nf_ref is > > > > > > > > > > > > > > set to > > > > > > > > > > > > > > REFCOUNT_SATURATED, and the 'nf' > > > > > > > > > > > > > > gets no chance of being freed. > > > > > > > > > > > > > > > > > > > > > > > > > > > > nfsd_file_put() can also race with > > > > > > > > > > > > > > nfsd_file_cond_queue(): > > > > > > > > > > > > > > * In nfsd_file_put(), nf->nf_ref is 1, so > > > > > > > > > > > > > > it tries > > > > > > > > > > > > > > to do > > > > > > > > > > > > > > nfsd_file_lru_add(). > > > > > > > > > > > > > > * nfsd_file_lru_add() sets REFERENCED bit > > > > > > > > > > > > > > and > > > > > > > > > > > > > > returns true. > > > > > > > > > > > > > > * Some userland application runs 'exportfs > > > > > > > > > > > > > > -f' or > > > > > > > > > > > > > > something > > > > > > > > > > > > > > like > > > > > > > > > > > > > > that, which triggers > > > > > > > > > > > > > > __nfsd_file_cache_purge() -> > > > > > > > > > > > > > > nfsd_file_cond_queue(). > > > > > > > > > > > > > > * In nfsd_file_cond_queue(), it runs [if > > > > > > > > > > > > > > (!nfsd_file_unhash(nf))], > > > > > > > > > > > > > > unhash is done > > > > > > > > > > > > > > successfully. > > > > > > > > > > > > > > * nfsd_file_cond_queue() runs [if > > > > > > > > > > > > > > (!nfsd_file_get(nf))], > > > > > > > > > > > > > > now > > > > > > > > > > > > > > nf->nf_ref goes to 2. > > > > > > > > > > > > > > * nfsd_file_cond_queue() runs [if > > > > > > > > > > > > > > (nfsd_file_lru_remove(nf))], > > > > > > > > > > > > > > it succeeds. > > > > > > > > > > > > > > * nfsd_file_cond_queue() runs [if > > > > > > > > > > > > > > (refcount_sub_and_test(decrement, > > > > > > > > > > > > > > &nf->nf_ref))] > > > > > > > > > > > > > > (with "decrement" being 2), so the nf- > > > > > > > > > > > > > > >nf_ref > > > > > > > > > > > > > > goes to 0, > > > > > > > > > > > > > > the > > > > > > > > > > > > > > 'nf' > > > > > > > > > > > > > > is added to the > > > > > > > > > > > > > > dispose list [list_add(&nf->nf_lru, > > > > > > > > > > > > > > dispose)] > > > > > > > > > > > > > > * nfsd_file_put() detects NFSD_FILE_HASHED > > > > > > > > > > > > > > bit is > > > > > > > > > > > > > > cleared, > > > > > > > > > > > > > > so > > > > > > > > > > > > > > it > > > > > > > > > > > > > > tries to remove > > > > > > > > > > > > > > the 'nf' from the LRU [if > > > > > > > > > > > > > > (!nfsd_file_lru_remove(nf))], > > > > > > > > > > > > > > although > > > > > > > > > > > > > > the 'nf' is not > > > > > > > > > > > > > > in the LRU, but it is linked in the > > > > > > > > > > > > > > 'dispose' > > > > > > > > > > > > > > list, > > > > > > > > > > > > > > nfsd_file_lru_remove() simply > > > > > > > > > > > > > > treats it as part of the LRU and removes > > > > > > > > > > > > > > it. This > > > > > > > > > > > > > > leads > > > > > > > > > > > > > > to > > > > > > > > > > > > > > its removal from > > > > > > > > > > > > > > the 'dispose' list! > > > > > > > > > > > > > > * Now nf->ref is 0, unhashed. > > > > > > > > > > > > > > nfsd_file_put() > > > > > > > > > > > > > > continues its > > > > > > > > > > > > > > execution and set > > > > > > > > > > > > > > nf->nf_ref to REFCOUNT_SATURATED. > > > > > > > > > > > > > > > > > > > > > > > > > > > > As shown in the above analysis, using nf_lru > > > > > > > > > > > > > > for both > > > > > > > > > > > > > > the LRU > > > > > > > > > > > > > > list and > > > > > > > > > > > > > > dispose list > > > > > > > > > > > > > > can cause the leaks. This patch adds a new > > > > > > > > > > > > > > list_head > > > > > > > > > > > > > > nf_gc in > > > > > > > > > > > > > > struct > > > > > > > > > > > > > > nfsd_file, and uses > > > > > > > > > > > > > > it for the dispose list. It's not expected to > > > > > > > > > > > > > > have a > > > > > > > > > > > > > > nfsd_file > > > > > > > > > > > > > > unhashed but it's not > > > > > > > > > > > > > > added to the dispose list, so in > > > > > > > > > > > > > > nfsd_file_cond_queue() and > > > > > > > > > > > > > > nfsd_file_lru_cb() nfsd_file > > > > > > > > > > > > > > is unhashed after being added to the dispose > > > > > > > > > > > > > > list. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I don't see where we require the object to be > > > > > > > > > > > > > either > > > > > > > > > > > > > hashed or > > > > > > > > > > > > > on > > > > > > > > > > > > > the > > > > > > > > > > > > > dispose list. I think you probably just want > > > > > > > > > > > > > to do a > > > > > > > > > > > > > patch > > > > > > > > > > > > > that > > > > > > > > > > > > > changes the dispose list to use a dedicated > > > > > > > > > > > > > list_head > > > > > > > > > > > > > without > > > > > > > > > > > > > reordering when the these things are unhashed. > > > > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Youzhong Yang > > > > > > > > > > > > > > <youzhong@xxxxxxxxx> > > > > > > > > > > > > > > --- > > > > > > > > > > > > > > fs/nfsd/filecache.c | 23 ++++++++++++++----- > > > > > > > > > > > > > > ---- > > > > > > > > > > > > > > fs/nfsd/filecache.h | 1 + > > > > > > > > > > > > > > 2 files changed, 15 insertions(+), 9 > > > > > > > > > > > > > > deletions(-) > > > > > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/fs/nfsd/filecache.c > > > > > > > > > > > > > > b/fs/nfsd/filecache.c > > > > > > > > > > > > > > index ad9083ca144b..3aef2ddfce94 100644 > > > > > > > > > > > > > > --- a/fs/nfsd/filecache.c > > > > > > > > > > > > > > +++ b/fs/nfsd/filecache.c > > > > > > > > > > > > > > @@ -216,6 +216,7 @@ nfsd_file_alloc(struct > > > > > > > > > > > > > > net *net, > > > > > > > > > > > > > > struct > > > > > > > > > > > > > > inode > > > > > > > > > > > > > > *inode, unsigned char need, > > > > > > > > > > > > > > return NULL; > > > > > > > > > > > > > > > > > > > > > > > > > > > > INIT_LIST_HEAD(&nf->nf_lru); > > > > > > > > > > > > > > + INIT_LIST_HEAD(&nf->nf_gc); > > > > > > > > > > > > > > nf->nf_birthtime = ktime_get(); > > > > > > > > > > > > > > nf->nf_file = NULL; > > > > > > > > > > > > > > nf->nf_cred = get_current_cred(); > > > > > > > > > > > > > > @@ -393,8 +394,8 @@ > > > > > > > > > > > > > > nfsd_file_dispose_list(struct > > > > > > > > > > > > > > list_head > > > > > > > > > > > > > > *dispose) > > > > > > > > > > > > > > struct nfsd_file *nf; > > > > > > > > > > > > > > > > > > > > > > > > > > > > while (!list_empty(dispose)) { > > > > > > > > > > > > > > - nf = > > > > > > > > > > > > > > list_first_entry(dispose, struct > > > > > > > > > > > > > > nfsd_file, > > > > > > > > > > > > > > nf_lru); > > > > > > > > > > > > > > - list_del_init(&nf->nf_lru); > > > > > > > > > > > > > > + nf = > > > > > > > > > > > > > > list_first_entry(dispose, struct > > > > > > > > > > > > > > nfsd_file, > > > > > > > > > > > > > > nf_gc); > > > > > > > > > > > > > > + list_del_init(&nf->nf_gc); > > > > > > > > > > > > > > nfsd_file_free(nf); > > > > > > > > > > > > > > } > > > > > > > > > > > > > > } > > > > > > > > > > > > > > @@ -411,12 +412,12 @@ > > > > > > > > > > > > > > nfsd_file_dispose_list_delayed(struct > > > > > > > > > > > > > > list_head *dispose) > > > > > > > > > > > > > > { > > > > > > > > > > > > > > while(!list_empty(dispose)) { > > > > > > > > > > > > > > struct nfsd_file *nf = > > > > > > > > > > > > > > list_first_entry(dispose, > > > > > > > > > > > > > > - > > > > > > > > > > > > > > struct > > > > > > > > > > > > > > nfsd_file, > > > > > > > > > > > > > > nf_lru); > > > > > > > > > > > > > > + > > > > > > > > > > > > > > struct > > > > > > > > > > > > > > nfsd_file, > > > > > > > > > > > > > > nf_gc); > > > > > > > > > > > > > > struct nfsd_net *nn = > > > > > > > > > > > > > > net_generic(nf- > > > > > > > > > > > > > > > nf_net, > > > > > > > > > > > > > > nfsd_net_id); > > > > > > > > > > > > > > struct nfsd_fcache_disposal > > > > > > > > > > > > > > *l = nn- > > > > > > > > > > > > > > > fcache_disposal; > > > > > > > > > > > > > > > > > > > > > > > > > > > > spin_lock(&l->lock); > > > > > > > > > > > > > > - list_move_tail(&nf->nf_lru, > > > > > > > > > > > > > > &l- > > > > > > > > > > > > > > > freeme); > > > > > > > > > > > > > > + list_move_tail(&nf->nf_gc, > > > > > > > > > > > > > > &l- > > > > > > > > > > > > > > > freeme); > > > > > > > > > > > > > > spin_unlock(&l->lock); > > > > > > > > > > > > > > svc_wake_up(nn->nfsd_serv); > > > > > > > > > > > > > > } > > > > > > > > > > > > > > @@ -502,8 +503,10 @@ nfsd_file_lru_cb(struct > > > > > > > > > > > > > > list_head *item, > > > > > > > > > > > > > > struct > > > > > > > > > > > > > > list_lru_one *lru, > > > > > > > > > > > > > > } > > > > > > > > > > > > > > > > > > > > > > > > > > > > /* Refcount went to zero. Unhash it > > > > > > > > > > > > > > and queue > > > > > > > > > > > > > > it to > > > > > > > > > > > > > > the > > > > > > > > > > > > > > dispose list */ > > > > > > > > > > > > > > + list_lru_isolate(lru, &nf->nf_lru); > > > > > > > > > > > > > > + list_add(&nf->nf_gc, head); > > > > > > > > > > > > > > + /* Unhash after removing from LRU and > > > > > > > > > > > > > > adding > > > > > > > > > > > > > > to > > > > > > > > > > > > > > dispose > > > > > > > > > > > > > > list */ > > > > > > > > > > > > > > nfsd_file_unhash(nf); > > > > > > > > > > > > > > - list_lru_isolate_move(lru, &nf- > > > > > > > > > > > > > > >nf_lru, > > > > > > > > > > > > > > head); > > > > > > > > > > > > > > > > > > > > > > > > > > I don't see the point in reordering these > > > > > > > > > > > > > operations. > > > > > > > > > > > > > Hashing > > > > > > > > > > > > > is > > > > > > > > > > > > > all > > > > > > > > > > > > > about making the thing findable by nfsd > > > > > > > > > > > > > operations. The > > > > > > > > > > > > > _last_ > > > > > > > > > > > > > thing we > > > > > > > > > > > > > want to do is put it on the dispose list while > > > > > > > > > > > > > the > > > > > > > > > > > > > thing can > > > > > > > > > > > > > still > > > > > > > > > > > > > be > > > > > > > > > > > > > found by nfsd threads doing operations. > > > > > > > > > > > > > > > > > > > > > > > > > > > this_cpu_inc(nfsd_file_evictions); > > > > > > > > > > > > > > trace_nfsd_file_gc_disposed(nf); > > > > > > > > > > > > > > return LRU_REMOVED; > > > > > > > > > > > > > > @@ -565,7 +568,7 @@ > > > > > > > > > > > > > > nfsd_file_cond_queue(struct > > > > > > > > > > > > > > nfsd_file > > > > > > > > > > > > > > *nf, > > > > > > > > > > > > > > struct > > > > > > > > > > > > > > list_head *dispose) > > > > > > > > > > > > > > int decrement = 1; > > > > > > > > > > > > > > > > > > > > > > > > > > > > /* If we raced with someone else > > > > > > > > > > > > > > unhashing, > > > > > > > > > > > > > > ignore it > > > > > > > > > > > > > > */ > > > > > > > > > > > > > > - if (!nfsd_file_unhash(nf)) > > > > > > > > > > > > > > + if (!test_bit(NFSD_FILE_HASHED, &nf- > > > > > > > > > > > > > > > nf_flags)) > > > > > > > > > > > > > > > > > > > > > > > > > > The above change looks wrong. I don't think we > > > > > > > > > > > > > need to > > > > > > > > > > > > > change > > > > > > > > > > > > > this. > > > > > > > > > > > > > > > > > > > > > > > > > > > return; > > > > > > > > > > > > > > > > > > > > > > > > > > > > /* If we can't get a reference, > > > > > > > > > > > > > > ignore it */ > > > > > > > > > > > > > > @@ -578,7 +581,9 @@ > > > > > > > > > > > > > > nfsd_file_cond_queue(struct > > > > > > > > > > > > > > nfsd_file > > > > > > > > > > > > > > *nf, > > > > > > > > > > > > > > struct > > > > > > > > > > > > > > list_head *dispose) > > > > > > > > > > > > > > > > > > > > > > > > > > > > /* If refcount goes to 0, then put on > > > > > > > > > > > > > > the > > > > > > > > > > > > > > dispose > > > > > > > > > > > > > > list */ > > > > > > > > > > > > > > if (refcount_sub_and_test(decrement, > > > > > > > > > > > > > > &nf- > > > > > > > > > > > > > > > nf_ref)) { > > > > > > > > > > > > > > - list_add(&nf->nf_lru, > > > > > > > > > > > > > > dispose); > > > > > > > > > > > > > > + list_add(&nf->nf_gc, > > > > > > > > > > > > > > dispose); > > > > > > > > > > > > > > + /* Unhash after adding to > > > > > > > > > > > > > > dispose > > > > > > > > > > > > > > list */ > > > > > > > > > > > > > > + nfsd_file_unhash(nf); > > > > > > > > > > > > > > > > > > > > > > > > > > This too looks wrong? Maybe I'm unclear on the > > > > > > > > > > > > > race > > > > > > > > > > > > > you're > > > > > > > > > > > > > trying > > > > > > > > > > > > > to > > > > > > > > > > > > > fix with this? What's the harm in unhashing it > > > > > > > > > > > > > early? > > > > > > > > > > > > > > > > > > > > > > > > > > > trace_nfsd_file_closing(nf); > > > > > > > > > > > > > > } > > > > > > > > > > > > > > } > > > > > > > > > > > > > > @@ -654,8 +659,8 @@ > > > > > > > > > > > > > > nfsd_file_close_inode_sync(struct > > > > > > > > > > > > > > inode > > > > > > > > > > > > > > *inode) > > > > > > > > > > > > > > > > > > > > > > > > > > > > nfsd_file_queue_for_close(inode, > > > > > > > > > > > > > > &dispose); > > > > > > > > > > > > > > while (!list_empty(&dispose)) { > > > > > > > > > > > > > > - nf = > > > > > > > > > > > > > > list_first_entry(&dispose, > > > > > > > > > > > > > > struct > > > > > > > > > > > > > > nfsd_file, > > > > > > > > > > > > > > nf_lru); > > > > > > > > > > > > > > - list_del_init(&nf->nf_lru); > > > > > > > > > > > > > > + nf = > > > > > > > > > > > > > > list_first_entry(&dispose, > > > > > > > > > > > > > > struct > > > > > > > > > > > > > > nfsd_file, > > > > > > > > > > > > > > nf_gc); > > > > > > > > > > > > > > + list_del_init(&nf->nf_gc); > > > > > > > > > > > > > > nfsd_file_free(nf); > > > > > > > > > > > > > > } > > > > > > > > > > > > > > } > > > > > > > > > > > > > > diff --git a/fs/nfsd/filecache.h > > > > > > > > > > > > > > b/fs/nfsd/filecache.h > > > > > > > > > > > > > > index c61884def906..3fbec24eea6c 100644 > > > > > > > > > > > > > > --- a/fs/nfsd/filecache.h > > > > > > > > > > > > > > +++ b/fs/nfsd/filecache.h > > > > > > > > > > > > > > @@ -44,6 +44,7 @@ struct nfsd_file { > > > > > > > > > > > > > > > > > > > > > > > > > > > > struct nfsd_file_mark *nf_mark; > > > > > > > > > > > > > > struct list_head nf_lru; > > > > > > > > > > > > > > + struct list_head nf_gc; > > > > > > > > > > > > > > struct rcu_head nf_rcu; > > > > > > > > > > > > > > ktime_t nf_birthtime; > > > > > > > > > > > > > > }; > > > > > > > > > > > > > > -- > > > > > > > > > > > > > > 2.34.1 > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Thu, Jul 4, 2024 at 7:14 AM Jeff Layton > > > > > > > > > > > > > > <jlayton@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Wed, 2024-07-03 at 16:46 -0400, Youzhong > > > > > > > > > > > > > > > Yang > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > Thank you Chuck. Here are my quick > > > > > > > > > > > > > > > > answers to > > > > > > > > > > > > > > > > your > > > > > > > > > > > > > > > > comments: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - I don't have a quick reproducer. I > > > > > > > > > > > > > > > > reproduced > > > > > > > > > > > > > > > > it by > > > > > > > > > > > > > > > > using > > > > > > > > > > > > > > > > hundreds > > > > > > > > > > > > > > > > of nfs clients generating +600K ops under > > > > > > > > > > > > > > > > our > > > > > > > > > > > > > > > > workload in > > > > > > > > > > > > > > > > the > > > > > > > > > > > > > > > > testing > > > > > > > > > > > > > > > > environment. Theoretically it should be > > > > > > > > > > > > > > > > possible > > > > > > > > > > > > > > > > to > > > > > > > > > > > > > > > > simplify > > > > > > > > > > > > > > > > the > > > > > > > > > > > > > > > > reproduction but I am still working on > > > > > > > > > > > > > > > > it. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - I understand zfs is an out-of-tree > > > > > > > > > > > > > > > > file > > > > > > > > > > > > > > > > system. That's > > > > > > > > > > > > > > > > fine. But > > > > > > > > > > > > > > > > this leaking can happen to any file > > > > > > > > > > > > > > > > system, and > > > > > > > > > > > > > > > > leaking > > > > > > > > > > > > > > > > is > > > > > > > > > > > > > > > > not a good > > > > > > > > > > > > > > > > thing no matter what file system it is. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - I will try to come up with a > > > > > > > > > > > > > > > > reproducer using > > > > > > > > > > > > > > > > xfs or > > > > > > > > > > > > > > > > btrfs > > > > > > > > > > > > > > > > if possible. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Now back to the problem itself, here are > > > > > > > > > > > > > > > > my > > > > > > > > > > > > > > > > findings: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - nfsd_file_put() in one thread can race > > > > > > > > > > > > > > > > with > > > > > > > > > > > > > > > > another > > > > > > > > > > > > > > > > thread > > > > > > > > > > > > > > > > doing > > > > > > > > > > > > > > > > garbage collection (running > > > > > > > > > > > > > > > > nfsd_file_gc() -> > > > > > > > > > > > > > > > > list_lru_walk() > > > > > > > > > > > > > > > > -> > > > > > > > > > > > > > > > > nfsd_file_lru_cb()): > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > * In nfsd_file_put(), nf->nf_ref is 1, > > > > > > > > > > > > > > > > so it > > > > > > > > > > > > > > > > tries to > > > > > > > > > > > > > > > > do > > > > > > > > > > > > > > > > nfsd_file_lru_add(). > > > > > > > > > > > > > > > > * nfsd_file_lru_add() returns true > > > > > > > > > > > > > > > > (thus > > > > > > > > > > > > > > > > NFSD_FILE_REFERENCED bit > > > > > > > > > > > > > > > > set for nf->nf_flags) > > > > > > > > > > > > > > > > * garbage collector kicks in, > > > > > > > > > > > > > > > > nfsd_file_lru_cb() clears > > > > > > > > > > > > > > > > REFERENCED > > > > > > > > > > > > > > > > bit and returns LRU_ROTATE. > > > > > > > > > > > > > > > > * garbage collector kicks in again, > > > > > > > > > > > > > > > > nfsd_file_lru_cb() > > > > > > > > > > > > > > > > now > > > > > > > > > > > > > > > > decrements nf->nf_ref to 0, runs > > > > > > > > > > > > > > > > nfsd_file_unhash(), > > > > > > > > > > > > > > > > removes > > > > > > > > > > > > > > > > it from > > > > > > > > > > > > > > > > the LRU and adds to the dispose list > > > > > > > > > > > > > > > > [list_lru_isolate_move(lru, > > > > > > > > > > > > > > > > &nf->nf_lru, head);] > > > > > > > > > > > > > > > > * nfsd_file_put() detects > > > > > > > > > > > > > > > > NFSD_FILE_HASHED bit > > > > > > > > > > > > > > > > is > > > > > > > > > > > > > > > > cleared, > > > > > > > > > > > > > > > > so it > > > > > > > > > > > > > > > > tries to remove the 'nf' from the LRU [if > > > > > > > > > > > > > > > > (!nfsd_file_lru_remove(nf))] > > > > > > > > > > > > > > > > * The 'nf' has been added to the > > > > > > > > > > > > > > > > 'dispose' list > > > > > > > > > > > > > > > > by > > > > > > > > > > > > > > > > nfsd_file_lru_cb(), so > > > > > > > > > > > > > > > > nfsd_file_lru_remove(nf) > > > > > > > > > > > > > > > > simply > > > > > > > > > > > > > > > > treats > > > > > > > > > > > > > > > > it as > > > > > > > > > > > > > > > > part of the LRU and removes it, which > > > > > > > > > > > > > > > > leads it to > > > > > > > > > > > > > > > > be > > > > > > > > > > > > > > > > removed > > > > > > > > > > > > > > > > from the > > > > > > > > > > > > > > > > 'dispose' list. > > > > > > > > > > > > > > > > * At this moment, nf->nf_ref is 0, it's > > > > > > > > > > > > > > > > unhashed, and > > > > > > > > > > > > > > > > not > > > > > > > > > > > > > > > > on the > > > > > > > > > > > > > > > > LRU. nfsd_file_put() continues its > > > > > > > > > > > > > > > > execution [if > > > > > > > > > > > > > > > > (refcount_dec_and_test(&nf->nf_ref))], as > > > > > > > > > > > > > > > > nf- > > > > > > > > > > > > > > > > > nf_ref is > > > > > > > > > > > > > > > > already 0, now > > > > > > > > > > > > > > > > bad thing happens: nf->nf_ref is set to > > > > > > > > > > > > > > > > REFCOUNT_SATURATED, > > > > > > > > > > > > > > > > and the > > > > > > > > > > > > > > > > 'nf' is leaked. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > To make this happen, the right timing is > > > > > > > > > > > > > > > > crucial. > > > > > > > > > > > > > > > > It can > > > > > > > > > > > > > > > > be > > > > > > > > > > > > > > > > reproduced > > > > > > > > > > > > > > > > by adding artifical delays in > > > > > > > > > > > > > > > > filecache.c, or > > > > > > > > > > > > > > > > hammering > > > > > > > > > > > > > > > > the > > > > > > > > > > > > > > > > nfsd with > > > > > > > > > > > > > > > > tons of ops. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - Let's see how nfsd_file_put() can race > > > > > > > > > > > > > > > > with > > > > > > > > > > > > > > > > nfsd_file_cond_queue(): > > > > > > > > > > > > > > > > * In nfsd_file_put(), nf->nf_ref is 1, > > > > > > > > > > > > > > > > so it > > > > > > > > > > > > > > > > tries to > > > > > > > > > > > > > > > > do > > > > > > > > > > > > > > > > nfsd_file_lru_add(). > > > > > > > > > > > > > > > > * nfsd_file_lru_add() sets REFERENCED > > > > > > > > > > > > > > > > bit and > > > > > > > > > > > > > > > > returns > > > > > > > > > > > > > > > > true. > > > > > > > > > > > > > > > > * 'exportfs -f' or something like that > > > > > > > > > > > > > > > > triggers > > > > > > > > > > > > > > > > __nfsd_file_cache_purge() -> > > > > > > > > > > > > > > > > nfsd_file_cond_queue(). > > > > > > > > > > > > > > > > * In nfsd_file_cond_queue(), it runs > > > > > > > > > > > > > > > > [if > > > > > > > > > > > > > > > > (!nfsd_file_unhash(nf))], > > > > > > > > > > > > > > > > unhash is done successfully. > > > > > > > > > > > > > > > > * nfsd_file_cond_queue() runs [if > > > > > > > > > > > > > > > > (!nfsd_file_get(nf))], > > > > > > > > > > > > > > > > now > > > > > > > > > > > > > > > > nf->nf_ref goes to 2. > > > > > > > > > > > > > > > > * nfsd_file_cond_queue() runs [if > > > > > > > > > > > > > > > > (nfsd_file_lru_remove(nf))], it succeeds. > > > > > > > > > > > > > > > > * nfsd_file_cond_queue() runs [if > > > > > > > > > > > > > > > > (refcount_sub_and_test(decrement, > > > > > > > > > > > > > > > > &nf->nf_ref))] (with "decrement" being > > > > > > > > > > > > > > > > 2), so the > > > > > > > > > > > > > > > > nf- > > > > > > > > > > > > > > > > > nf_ref > > > > > > > > > > > > > > > > goes to > > > > > > > > > > > > > > > > 0, the 'nf' is added to the dispost list > > > > > > > > > > > > > > > > [list_add(&nf- > > > > > > > > > > > > > > > > > nf_lru, > > > > > > > > > > > > > > > > dispose)] > > > > > > > > > > > > > > > > * nfsd_file_put() detects > > > > > > > > > > > > > > > > NFSD_FILE_HASHED bit > > > > > > > > > > > > > > > > is > > > > > > > > > > > > > > > > cleared, > > > > > > > > > > > > > > > > so it > > > > > > > > > > > > > > > > tries to remove the 'nf' from the LRU [if > > > > > > > > > > > > > > > > (!nfsd_file_lru_remove(nf))], although > > > > > > > > > > > > > > > > the 'nf' > > > > > > > > > > > > > > > > is not in > > > > > > > > > > > > > > > > the > > > > > > > > > > > > > > > > LRU, but > > > > > > > > > > > > > > > > it is linked in the 'dispose' list, > > > > > > > > > > > > > > > > nfsd_file_lru_remove() > > > > > > > > > > > > > > > > simply > > > > > > > > > > > > > > > > treats it as part of the LRU and removes > > > > > > > > > > > > > > > > it. This > > > > > > > > > > > > > > > > leads > > > > > > > > > > > > > > > > to > > > > > > > > > > > > > > > > its removal > > > > > > > > > > > > > > > > from the 'dispose' list! > > > > > > > > > > > > > > > > * Now nf->ref is 0, unhashed. > > > > > > > > > > > > > > > > nfsd_file_put() > > > > > > > > > > > > > > > > continues > > > > > > > > > > > > > > > > its > > > > > > > > > > > > > > > > execution and sets nf->nf_ref to > > > > > > > > > > > > > > > > REFCOUNT_SATURATED. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The purpose of nf->nf_lru is problematic. > > > > > > > > > > > > > > > > As you > > > > > > > > > > > > > > > > can see, > > > > > > > > > > > > > > > > it > > > > > > > > > > > > > > > > is used > > > > > > > > > > > > > > > > for the LRU list, and also the 'dispose' > > > > > > > > > > > > > > > > list. > > > > > > > > > > > > > > > > Adding > > > > > > > > > > > > > > > > another > > > > > > > > > > > > > > > > 'struct > > > > > > > > > > > > > > > > list_head' specifically for the 'dispose' > > > > > > > > > > > > > > > > list > > > > > > > > > > > > > > > > seems to > > > > > > > > > > > > > > > > be a > > > > > > > > > > > > > > > > better > > > > > > > > > > > > > > > > way of fixing this race condition. Either > > > > > > > > > > > > > > > > way > > > > > > > > > > > > > > > > works for > > > > > > > > > > > > > > > > me. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Would you agree my above analysis makes > > > > > > > > > > > > > > > > sense? > > > > > > > > > > > > > > > > Thanks. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I think so. It's been a while since I've > > > > > > > > > > > > > > > done much > > > > > > > > > > > > > > > work in > > > > > > > > > > > > > > > this > > > > > > > > > > > > > > > code, > > > > > > > > > > > > > > > but it does sound like there is a race in > > > > > > > > > > > > > > > the LRU > > > > > > > > > > > > > > > handling. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Like Chuck said, the nf->nf_lru list should > > > > > > > > > > > > > > > be safe > > > > > > > > > > > > > > > to use > > > > > > > > > > > > > > > for > > > > > > > > > > > > > > > multiple > > > > > > > > > > > > > > > purposes, but that's only the case if we're > > > > > > > > > > > > > > > not > > > > > > > > > > > > > > > using that > > > > > > > > > > > > > > > list > > > > > > > > > > > > > > > as an > > > > > > > > > > > > > > > indicator. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The list_lru code does check this: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > if (!list_empty(item)) { > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ...so if we ever check this while it's > > > > > > > > > > > > > > > sitting on > > > > > > > > > > > > > > > the > > > > > > > > > > > > > > > dispose > > > > > > > > > > > > > > > list, it > > > > > > > > > > > > > > > will handle it incorrectly. It sounds like > > > > > > > > > > > > > > > that's > > > > > > > > > > > > > > > the root > > > > > > > > > > > > > > > cause of the > > > > > > > > > > > > > > > problem you're seeing? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > If so, then maybe a separate list_head for > > > > > > > > > > > > > > > disposal > > > > > > > > > > > > > > > would > > > > > > > > > > > > > > > be > > > > > > > > > > > > > > > better. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Here is my patch with signed-off-by: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > From: Youzhong Yang <youzhong@xxxxxxxxx> > > > > > > > > > > > > > > > > Date: Mon, 1 Jul 2024 06:45:22 -0400 > > > > > > > > > > > > > > > > Subject: [PATCH] nfsd: fix nfsd_file > > > > > > > > > > > > > > > > leaking due > > > > > > > > > > > > > > > > to race > > > > > > > > > > > > > > > > condition and early > > > > > > > > > > > > > > > > unhash > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Youzhong Yang > > > > > > > > > > > > > > > > <youzhong@xxxxxxxxx> > > > > > > > > > > > > > > > > --- > > > > > > > > > > > > > > > > fs/nfsd/filecache.c | 14 +++++++++++++- > > > > > > > > > > > > > > > > 1 file changed, 13 insertions(+), 1 > > > > > > > > > > > > > > > > deletion(-) > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/fs/nfsd/filecache.c > > > > > > > > > > > > > > > > b/fs/nfsd/filecache.c > > > > > > > > > > > > > > > > index 1a6d5d000b85..2323829f7208 100644 > > > > > > > > > > > > > > > > --- a/fs/nfsd/filecache.c > > > > > > > > > > > > > > > > +++ b/fs/nfsd/filecache.c > > > > > > > > > > > > > > > > @@ -389,6 +389,17 @@ nfsd_file_put(struct > > > > > > > > > > > > > > > > nfsd_file *nf) > > > > > > > > > > > > > > > > if > > > > > > > > > > > > > > > > (!nfsd_file_lru_remove(nf)) > > > > > > > > > > > > > > > > return; > > > > > > > > > > > > > > > > } > > > > > > > > > > > > > > > > + /* > > > > > > > > > > > > > > > > + * Racing with > > > > > > > > > > > > > > > > nfsd_file_cond_queue() or > > > > > > > > > > > > > > > > nfsd_file_lru_cb(), > > > > > > > > > > > > > > > > + * it's unhashed but then > > > > > > > > > > > > > > > > removed > > > > > > > > > > > > > > > > from > > > > > > > > > > > > > > > > the > > > > > > > > > > > > > > > > dispose list, > > > > > > > > > > > > > > > > + * so we need to free it. > > > > > > > > > > > > > > > > + */ > > > > > > > > > > > > > > > > + if (refcount_read(&nf- > > > > > > > > > > > > > > > > >nf_ref) == > > > > > > > > > > > > > > > > 0 && > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > A refcount_read in this path is a red flag > > > > > > > > > > > > > > > to me. > > > > > > > > > > > > > > > Anytime > > > > > > > > > > > > > > > you're just > > > > > > > > > > > > > > > looking at the refcount without changing > > > > > > > > > > > > > > > anything > > > > > > > > > > > > > > > just > > > > > > > > > > > > > > > screams > > > > > > > > > > > > > > > out > > > > > > > > > > > > > > > "race condition". > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > In this case, what guarantee is there that > > > > > > > > > > > > > > > this > > > > > > > > > > > > > > > won't run > > > > > > > > > > > > > > > afoul > > > > > > > > > > > > > > > of the > > > > > > > > > > > > > > > timing? We could check this and find out > > > > > > > > > > > > > > > it's 1 > > > > > > > > > > > > > > > just before > > > > > > > > > > > > > > > it > > > > > > > > > > > > > > > goes to > > > > > > > > > > > > > > > 0 and you check the other conditions. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Does anything prevent that? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > + > > > > > > > > > > > > > > > > !test_bit(NFSD_FILE_HASHED, > > > > > > > > > > > > > > > > &nf- > > > > > > > > > > > > > > > > > nf_flags) && > > > > > > > > > > > > > > > > + list_empty(&nf- > > > > > > > > > > > > > > > > >nf_lru)) { > > > > > > > > > > > > > > > > + > > > > > > > > > > > > > > > > nfsd_file_free(nf); > > > > > > > > > > > > > > > > + return; > > > > > > > > > > > > > > > > + } > > > > > > > > > > > > > > > > } > > > > > > > > > > > > > > > > if (refcount_dec_and_test(&nf- > > > > > > > > > > > > > > > > >nf_ref)) > > > > > > > > > > > > > > > > nfsd_file_free(nf); > > > > > > > > > > > > > > > > @@ -576,7 +587,7 @@ > > > > > > > > > > > > > > > > nfsd_file_cond_queue(struct > > > > > > > > > > > > > > > > nfsd_file > > > > > > > > > > > > > > > > *nf, struct > > > > > > > > > > > > > > > > list_head *dispose) > > > > > > > > > > > > > > > > int decrement = 1; > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > /* If we raced with someone else > > > > > > > > > > > > > > > > unhashing, > > > > > > > > > > > > > > > > ignore it > > > > > > > > > > > > > > > > */ > > > > > > > > > > > > > > > > - if (!nfsd_file_unhash(nf)) > > > > > > > > > > > > > > > > + if (!test_bit(NFSD_FILE_HASHED, > > > > > > > > > > > > > > > > &nf- > > > > > > > > > > > > > > > > > nf_flags)) > > > > > > > > > > > > > > > > return; > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Same here: you're just testing for the > > > > > > > > > > > > > > > HASHED bit, > > > > > > > > > > > > > > > but > > > > > > > > > > > > > > > could > > > > > > > > > > > > > > > this also > > > > > > > > > > > > > > > race with someone who is setting it just > > > > > > > > > > > > > > > after you > > > > > > > > > > > > > > > get > > > > > > > > > > > > > > > here. > > > > > > > > > > > > > > > Why is > > > > > > > > > > > > > > > that not a problem? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > /* If we can't get a reference, > > > > > > > > > > > > > > > > ignore it > > > > > > > > > > > > > > > > */ > > > > > > > > > > > > > > > > @@ -590,6 +601,7 @@ > > > > > > > > > > > > > > > > nfsd_file_cond_queue(struct > > > > > > > > > > > > > > > > nfsd_file > > > > > > > > > > > > > > > > *nf, struct > > > > > > > > > > > > > > > > list_head *dispose) > > > > > > > > > > > > > > > > /* If refcount goes to 0, then > > > > > > > > > > > > > > > > put on the > > > > > > > > > > > > > > > > dispose > > > > > > > > > > > > > > > > list */ > > > > > > > > > > > > > > > > if > > > > > > > > > > > > > > > > (refcount_sub_and_test(decrement, &nf- > > > > > > > > > > > > > > > > > nf_ref)) { > > > > > > > > > > > > > > > > list_add(&nf->nf_lru, > > > > > > > > > > > > > > > > dispose); > > > > > > > > > > > > > > > > + nfsd_file_unhash(nf); > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > trace_nfsd_file_closing(nf); > > > > > > > > > > > > > > > > } > > > > > > > > > > > > > > > > } > > > > > > > > > > > > > > > > -- > > > > > > > > > > > > > > > > 2.43.0 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Wed, Jul 3, 2024 at 2:21 PM Chuck > > > > > > > > > > > > > > > > Lever > > > > > > > > > > > > > > > > <chuck.lever@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Wed, Jul 03, 2024 at 10:12:33AM - > > > > > > > > > > > > > > > > > 0400, > > > > > > > > > > > > > > > > > Youzhong Yang > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > Hello, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I'd like to report a nfsd_file > > > > > > > > > > > > > > > > > > leaking issue > > > > > > > > > > > > > > > > > > and > > > > > > > > > > > > > > > > > > propose > > > > > > > > > > > > > > > > > > a fix for it. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > When I tested Linux kernel 6.8 and > > > > > > > > > > > > > > > > > > 6.6, I > > > > > > > > > > > > > > > > > > noticed > > > > > > > > > > > > > > > > > > nfsd_file leaks > > > > > > > > > > > > > > > > > > which led to undestroyable file > > > > > > > > > > > > > > > > > > systems > > > > > > > > > > > > > > > > > > (zfs), > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks for the report. Some initial > > > > > > > > > > > > > > > > > comments: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - Do you have a specific reproducer? In > > > > > > > > > > > > > > > > > other > > > > > > > > > > > > > > > > > words, > > > > > > > > > > > > > > > > > what > > > > > > > > > > > > > > > > > is the > > > > > > > > > > > > > > > > > simplest program that can run on an > > > > > > > > > > > > > > > > > NFS > > > > > > > > > > > > > > > > > client that > > > > > > > > > > > > > > > > > will > > > > > > > > > > > > > > > > > trigger > > > > > > > > > > > > > > > > > this leak, and can you post it? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - "zfs" is an out-of-tree file system, > > > > > > > > > > > > > > > > > so it's > > > > > > > > > > > > > > > > > not > > > > > > > > > > > > > > > > > directly > > > > > > > > > > > > > > > > > supported for NFSD. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - The guidelines for patch submission > > > > > > > > > > > > > > > > > require > > > > > > > > > > > > > > > > > us to fix > > > > > > > > > > > > > > > > > issues in > > > > > > > > > > > > > > > > > upstream Linux first (currently > > > > > > > > > > > > > > > > > that's v6.10- > > > > > > > > > > > > > > > > > rc6). > > > > > > > > > > > > > > > > > Then > > > > > > > > > > > > > > > > > that fix > > > > > > > > > > > > > > > > > can be backported to older stable > > > > > > > > > > > > > > > > > kernels > > > > > > > > > > > > > > > > > like 6.6. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Can you reproduce the leak with one of > > > > > > > > > > > > > > > > > the in- > > > > > > > > > > > > > > > > > kernel > > > > > > > > > > > > > > > > > filesystems > > > > > > > > > > > > > > > > > (either xfs or btrfs would be great) > > > > > > > > > > > > > > > > > and with > > > > > > > > > > > > > > > > > NFSD in > > > > > > > > > > > > > > > > > 6.10- > > > > > > > > > > > > > > > > > rc6? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > One more comment below. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > here are some examples: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > crash> struct nfsd_file -x > > > > > > > > > > > > > > > > > > ffff88e160db0460 > > > > > > > > > > > > > > > > > > struct nfsd_file { > > > > > > > > > > > > > > > > > > nf_rlist = { > > > > > > > > > > > > > > > > > > rhead = { > > > > > > > > > > > > > > > > > > next = 0xffff8921fa2392f1 > > > > > > > > > > > > > > > > > > }, > > > > > > > > > > > > > > > > > > next = 0x0 > > > > > > > > > > > > > > > > > > }, > > > > > > > > > > > > > > > > > > nf_inode = 0xffff8882bc312ef8, > > > > > > > > > > > > > > > > > > nf_file = 0xffff88e2015b1500, > > > > > > > > > > > > > > > > > > nf_cred = 0xffff88e3ab0e7800, > > > > > > > > > > > > > > > > > > nf_net = 0xffffffff83d41600 > > > > > > > > > > > > > > > > > > <init_net>, > > > > > > > > > > > > > > > > > > nf_flags = 0x8, > > > > > > > > > > > > > > > > > > nf_ref = { > > > > > > > > > > > > > > > > > > refs = { > > > > > > > > > > > > > > > > > > counter = 0xc0000000 > > > > > > > > > > > > > > > > > > } > > > > > > > > > > > > > > > > > > }, > > > > > > > > > > > > > > > > > > nf_may = 0x4, > > > > > > > > > > > > > > > > > > nf_mark = 0xffff88e1bddfb320, > > > > > > > > > > > > > > > > > > nf_lru = { > > > > > > > > > > > > > > > > > > next = 0xffff88e160db04a8, > > > > > > > > > > > > > > > > > > prev = 0xffff88e160db04a8 > > > > > > > > > > > > > > > > > > }, > > > > > > > > > > > > > > > > > > nf_rcu = { > > > > > > > > > > > > > > > > > > next = 0x10000000000, > > > > > > > > > > > > > > > > > > func = 0x0 > > > > > > > > > > > > > > > > > > }, > > > > > > > > > > > > > > > > > > nf_birthtime = 0x73d22fc1728 > > > > > > > > > > > > > > > > > > } > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > crash> struct > > > > > > > > > > > > > > > > > > nfsd_file.nf_flags,nf_ref.refs.counte > > > > > > > > > > > > > > > > > > r,nf_lru > > > > > > > > > > > > > > > > > > ,nf_file > > > > > > > > > > > > > > > > > > -x > > > > > > > > > > > > > > > > > > ffff88839a53d850 > > > > > > > > > > > > > > > > > > nf_flags = 0x8, > > > > > > > > > > > > > > > > > > nf_ref.refs.counter = 0x0 > > > > > > > > > > > > > > > > > > nf_lru = { > > > > > > > > > > > > > > > > > > next = 0xffff88839a53d898, > > > > > > > > > > > > > > > > > > prev = 0xffff88839a53d898 > > > > > > > > > > > > > > > > > > }, > > > > > > > > > > > > > > > > > > nf_file = 0xffff88810ede8700, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > crash> struct > > > > > > > > > > > > > > > > > > nfsd_file.nf_flags,nf_ref.refs.counte > > > > > > > > > > > > > > > > > > r,nf_lru > > > > > > > > > > > > > > > > > > ,nf_file > > > > > > > > > > > > > > > > > > -x > > > > > > > > > > > > > > > > > > ffff88c32b11e850 > > > > > > > > > > > > > > > > > > nf_flags = 0x8, > > > > > > > > > > > > > > > > > > nf_ref.refs.counter = 0x0 > > > > > > > > > > > > > > > > > > nf_lru = { > > > > > > > > > > > > > > > > > > next = 0xffff88c32b11e898, > > > > > > > > > > > > > > > > > > prev = 0xffff88c32b11e898 > > > > > > > > > > > > > > > > > > }, > > > > > > > > > > > > > > > > > > nf_file = 0xffff88c20a701c00, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > crash> struct > > > > > > > > > > > > > > > > > > nfsd_file.nf_flags,nf_ref.refs.counte > > > > > > > > > > > > > > > > > > r,nf_lru > > > > > > > > > > > > > > > > > > ,nf_file > > > > > > > > > > > > > > > > > > -x > > > > > > > > > > > > > > > > > > ffff88e372709700 > > > > > > > > > > > > > > > > > > nf_flags = 0xc, > > > > > > > > > > > > > > > > > > nf_ref.refs.counter = 0x0 > > > > > > > > > > > > > > > > > > nf_lru = { > > > > > > > > > > > > > > > > > > next = 0xffff88e372709748, > > > > > > > > > > > > > > > > > > prev = 0xffff88e372709748 > > > > > > > > > > > > > > > > > > }, > > > > > > > > > > > > > > > > > > nf_file = 0xffff88e0725e6400, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > crash> struct > > > > > > > > > > > > > > > > > > nfsd_file.nf_flags,nf_ref.refs.counte > > > > > > > > > > > > > > > > > > r,nf_lru > > > > > > > > > > > > > > > > > > ,nf_file > > > > > > > > > > > > > > > > > > -x > > > > > > > > > > > > > > > > > > ffff8982864944d0 > > > > > > > > > > > > > > > > > > nf_flags = 0xc, > > > > > > > > > > > > > > > > > > nf_ref.refs.counter = 0x0 > > > > > > > > > > > > > > > > > > nf_lru = { > > > > > > > > > > > > > > > > > > next = 0xffff898286494518, > > > > > > > > > > > > > > > > > > prev = 0xffff898286494518 > > > > > > > > > > > > > > > > > > }, > > > > > > > > > > > > > > > > > > nf_file = 0xffff89803c0ff700, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The leak occurs when nfsd_file_put() > > > > > > > > > > > > > > > > > > races > > > > > > > > > > > > > > > > > > with > > > > > > > > > > > > > > > > > > nfsd_file_cond_queue() > > > > > > > > > > > > > > > > > > or nfsd_file_lru_cb(). With the > > > > > > > > > > > > > > > > > > following > > > > > > > > > > > > > > > > > > patch, I > > > > > > > > > > > > > > > > > > haven't observed > > > > > > > > > > > > > > > > > > any leak after a few days heavy nfs > > > > > > > > > > > > > > > > > > load: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Our patch submission guidelines require > > > > > > > > > > > > > > > > > a > > > > > > > > > > > > > > > > > Signed-off- > > > > > > > > > > > > > > > > > by: > > > > > > > > > > > > > > > > > line at the end of the patch > > > > > > > > > > > > > > > > > description. See > > > > > > > > > > > > > > > > > the "Sign > > > > > > > > > > > > > > > > > your work - > > > > > > > > > > > > > > > > > the Developer's Certificate of Origin" > > > > > > > > > > > > > > > > > section > > > > > > > > > > > > > > > > > of > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v6.10-rc6 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > (Needed here in case your fix is > > > > > > > > > > > > > > > > > acceptable). > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/fs/nfsd/filecache.c > > > > > > > > > > > > > > > > > > b/fs/nfsd/filecache.c > > > > > > > > > > > > > > > > > > index 1a6d5d000b85..2323829f7208 > > > > > > > > > > > > > > > > > > 100644 > > > > > > > > > > > > > > > > > > --- a/fs/nfsd/filecache.c > > > > > > > > > > > > > > > > > > +++ b/fs/nfsd/filecache.c > > > > > > > > > > > > > > > > > > @@ -389,6 +389,17 @@ > > > > > > > > > > > > > > > > > > nfsd_file_put(struct > > > > > > > > > > > > > > > > > > nfsd_file > > > > > > > > > > > > > > > > > > *nf) > > > > > > > > > > > > > > > > > > if (!nfsd_file_lru_remove(nf)) > > > > > > > > > > > > > > > > > > return; > > > > > > > > > > > > > > > > > > } > > > > > > > > > > > > > > > > > > + /* > > > > > > > > > > > > > > > > > > + * Racing with > > > > > > > > > > > > > > > > > > nfsd_file_cond_queue() or > > > > > > > > > > > > > > > > > > nfsd_file_lru_cb(), > > > > > > > > > > > > > > > > > > + * it's unhashed but then removed > > > > > > > > > > > > > > > > > > from the > > > > > > > > > > > > > > > > > > dispose > > > > > > > > > > > > > > > > > > list, > > > > > > > > > > > > > > > > > > + * so we need to free it. > > > > > > > > > > > > > > > > > > + */ > > > > > > > > > > > > > > > > > > + if (refcount_read(&nf->nf_ref) == 0 > > > > > > > > > > > > > > > > > > && > > > > > > > > > > > > > > > > > > + !test_bit(NFSD_FILE_HASHED, > > > > > > > > > > > > > > > > > > &nf- > > > > > > > > > > > > > > > > > > > nf_flags) && > > > > > > > > > > > > > > > > > > + list_empty(&nf->nf_lru)) { > > > > > > > > > > > > > > > > > > + nfsd_file_free(nf); > > > > > > > > > > > > > > > > > > + return; > > > > > > > > > > > > > > > > > > + } > > > > > > > > > > > > > > > > > > } > > > > > > > > > > > > > > > > > > if (refcount_dec_and_test(&nf- > > > > > > > > > > > > > > > > > > >nf_ref)) > > > > > > > > > > > > > > > > > > nfsd_file_free(nf); > > > > > > > > > > > > > > > > > > @@ -576,7 +587,7 @@ > > > > > > > > > > > > > > > > > > nfsd_file_cond_queue(struct > > > > > > > > > > > > > > > > > > nfsd_file > > > > > > > > > > > > > > > > > > *nf, struct > > > > > > > > > > > > > > > > > > list_head *dispose) > > > > > > > > > > > > > > > > > > int decrement = 1; > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > /* If we raced with someone else > > > > > > > > > > > > > > > > > > unhashing, > > > > > > > > > > > > > > > > > > ignore > > > > > > > > > > > > > > > > > > it > > > > > > > > > > > > > > > > > > */ > > > > > > > > > > > > > > > > > > - if (!nfsd_file_unhash(nf)) > > > > > > > > > > > > > > > > > > + if (!test_bit(NFSD_FILE_HASHED, > > > > > > > > > > > > > > > > > > &nf- > > > > > > > > > > > > > > > > > > > nf_flags)) > > > > > > > > > > > > > > > > > > return; > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > /* If we can't get a reference, > > > > > > > > > > > > > > > > > > ignore it > > > > > > > > > > > > > > > > > > */ > > > > > > > > > > > > > > > > > > @@ -590,6 +601,7 @@ > > > > > > > > > > > > > > > > > > nfsd_file_cond_queue(struct > > > > > > > > > > > > > > > > > > nfsd_file > > > > > > > > > > > > > > > > > > *nf, struct > > > > > > > > > > > > > > > > > > list_head *dispose) > > > > > > > > > > > > > > > > > > /* If refcount goes to 0, then put > > > > > > > > > > > > > > > > > > on the > > > > > > > > > > > > > > > > > > dispose > > > > > > > > > > > > > > > > > > list > > > > > > > > > > > > > > > > > > */ > > > > > > > > > > > > > > > > > > if > > > > > > > > > > > > > > > > > > (refcount_sub_and_test(decrement, > > > > > > > > > > > > > > > > > > &nf- > > > > > > > > > > > > > > > > > > > nf_ref)) > > > > > > > > > > > > > > > > > > { > > > > > > > > > > > > > > > > > > list_add(&nf->nf_lru, dispose); > > > > > > > > > > > > > > > > > > + nfsd_file_unhash(nf); > > > > > > > > > > > > > > > > > > trace_nfsd_file_closing(nf); > > > > > > > > > > > > > > > > > > } > > > > > > > > > > > > > > > > > > } > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Please kindly review the patch and > > > > > > > > > > > > > > > > > > let me > > > > > > > > > > > > > > > > > > know if it > > > > > > > > > > > > > > > > > > makes sense. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -Youzhong > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > > > > > > > > > Chuck Lever > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > > > > > > > Jeff Layton <jlayton@xxxxxxxxxxxxxxx> > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > > > > > Jeff Layton <jlayton@xxxxxxxxxxxxxxx> > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > > > > > Jeff Layton <jlayton@xxxxxxxxxx> > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > > > Jeff Layton <jlayton@xxxxxxxxxx> > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > Jeff Layton <jlayton@xxxxxxxxxx> > > > > > > > > > > > > > > -- > > > > > > > Jeff Layton <jlayton@xxxxxxxxxx> > > > > > > > > > > -- > > > > > Jeff Layton <jlayton@xxxxxxxxxx> > > > > > > > > > > -- > > > Jeff Layton <jlayton@xxxxxxxxxx> > > -- > Jeff Layton <jlayton@xxxxxxxxxx>
