On Thu, 24 Mar 2022 at 17:13, Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote: > > On Thu, Mar 24, 2022 at 4:50 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > > > > On Thu, 24 Mar 2022 at 09:44, Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote: > > > > > > On Thu, Mar 24, 2022 at 11:05 AM Linus Torvalds > > > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > On Wed, Mar 23, 2022 at 7:19 PM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote: > > > > > > > > > > After this commit, the rules of dentry allocations changed. > > > > > The dentry should be allocated by kmem_cache_alloc_lru() > > > > > > > > Yeah, I looked at that, but I can't find any way there could be other > > > > allocations - not only are there strict rules how to initialize > > > > everything, but the dentries are free'd using > > > > > > > > kmem_cache_free(dentry_cache, dentry); > > > > > > > > and as a result if they were allocated any other way I would expect > > > > things would go south very quickly. > > > > > > > > The only other thing I could come up with is some breakage in the > > > > superblock lifetime so that &dentry->d_sb->s_dentry_lru would have > > > > problems, but again, this is *such* core code and not some unusual > > > > path, that I would be very very surprised if it wouldn't have > > > > triggered other issues long long ago. > > > > > > > > That's why I'd be more inclined to worry about the list_lru code being > > > > somehow broken. > > > > > > > > > > I also have the same concern. I have been trying for a few hours to > > > reproduce this issue, but it didn't oops on my test machine. And I'll > > > continue reproducing this. > > > > syzbot triggered it 222 times in a day, so it's most likely real: > > https://syzkaller.appspot.com/bug?extid=f8c45ccc7d5d45fc5965 > > > > There are 2 reproducers, but they look completely different. May be a race. > > You may also try to use syzbot's patch testing feature to get some > > additional debug info. > > Do you know how to tell the syzbot to test the following patch? > I found some infos from github, it says "#syz test:", is it like the following? > Thanks. > > #syz test: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git > master Yes, this is correct. You can now see the request listed here: https://syzkaller.appspot.com/bug?extid=f8c45ccc7d5d45fc5965 but the patch was truncated (probably you email client messed whitespaces). In such case it's more reliable to attach the patch as text file. > diff --git a/mm/list_lru.c b/mm/list_lru.c > index c669d87001a6..ddb2ee627d32 100644 > --- a/mm/list_lru.c > +++ b/mm/list_lru.c > @@ -67,6 +67,7 @@ list_lru_from_kmem(struct list_lru *lru, int nid, void *ptr, > struct list_lru_node *nlru = &lru->node[nid]; > struct list_lru_one *l = &nlru->lru; > struct mem_cgroup *memcg = NULL; > + int kmemcg_id; > > if (!list_lru_memcg_aware(lru)) > goto out; > @@ -75,7 +76,13 @@ list_lru_from_kmem(struct list_lru *lru, int nid, void *ptr, > if (!memcg) > goto out; > > - l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg)); > + kmemcg_id = memcg_kmem_id(memcg); > + l = list_lru_from_memcg_idx(lru, nid, kmemcg_id); > + if (!l) { > + pr_info("BUG: the memcg(%px)->objcg(%px), kmemcg_id: %d\n", > + memcg, memcg->objcg, kmemcg_id); > + BUG(); > + } > out: > if (memcg_ptr) > *memcg_ptr = memcg;
