On Tue, 22 Jul 2014 13:45:52 -0400 "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote: > On Tue, Jul 22, 2014 at 12:41:31PM -0400, Jeff Layton wrote: > > There's a potential race between a lease break and DELEGRETURN call. > > > > Suppose a lease break comes in and queues the workqueue job for a > > delegation, but it doesn't run just yet. Then, a DELEGRETURN comes in > > finds the delegation and calls destroy_delegation on it to unhash it and > > put its primary reference. > > > > Next, the workqueue job runs and queues the delegation back onto the > > del_recall_lru list, issues the CB_RECALL and puts the final reference. > > With that, the final reference to the delegation is put, but it's still > > on the LRU list. > > > > When we go to unhash a delegation, it's because we intend to get rid of > > it soon afterward, so we don't want lease breaks to mess with it once > > that occurs. Fix this by bumping the dl_time whenever we unhash a > > delegation, to ensure that lease breaks don't monkey with it. > > Makes sense, thanks. Repeating from IRC: this fixes a regression from > 02e1215f9f7 "nfsd: Avoid taking state_lock while holding inode lock in > nfsd_break_one_deleg". (In my tree only.) > > --b. > > > > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxxxxxxx> > > --- > > fs/nfsd/nfs4state.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > > index 72da0d44e66b..a3a828d17563 100644 > > --- a/fs/nfsd/nfs4state.c > > +++ b/fs/nfsd/nfs4state.c > > @@ -660,6 +660,8 @@ unhash_delegation(struct nfs4_delegation *dp) > > > > spin_lock(&state_lock); > > dp->dl_stid.sc_type = NFS4_CLOSED_DELEG_STID; > > + /* Ensure that deleg break won't try to requeue it */ > > + ++dp->dl_time; > > spin_lock(&fp->fi_lock); > > list_del_init(&dp->dl_perclnt); > > list_del_init(&dp->dl_recall_lru); > > -- > > 1.9.3 > > Sorry, I think I sent you a version with an earlier description. Here's the one I meant to send: --------------------[snip]--------------------- [PATCH] nfsd: bump dl_time when unhashing delegation There's a potential race between a lease break and DELEGRETURN call. Suppose a lease break comes in and queues the workqueue job for a delegation, but it doesn't run just yet. Then, a DELEGRETURN comes in finds the delegation and calls destroy_delegation on it to unhash it and put its primary reference. Next, the workqueue job runs and queues the delegation back onto the del_recall_lru list, issues the CB_RECALL and puts the final reference. With that, the final reference to the delegation is put, but it's still on the LRU list. When we go to unhash a delegation, it's because we intend to get rid of it soon afterward, so we don't want lease breaks to mess with it once that occurs. Fix this by bumping the dl_time whenever we unhash a delegation, to ensure that lease breaks don't monkey with it. I believe this is a regression due to commit 02e1215f9f7 (nfsd: Avoid taking state_lock while holding inode lock in nfsd_break_one_deleg). Prior to that, the state_lock was held in the lm_break callback itself, and that would have prevented this race. Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxxxxxxx> --- fs/nfsd/nfs4state.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index 72da0d44e66b..a3a828d17563 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -660,6 +660,8 @@ unhash_delegation(struct nfs4_delegation *dp) spin_lock(&state_lock); dp->dl_stid.sc_type = NFS4_CLOSED_DELEG_STID; + /* Ensure that deleg break won't try to requeue it */ + ++dp->dl_time; spin_lock(&fp->fi_lock); list_del_init(&dp->dl_perclnt); list_del_init(&dp->dl_recall_lru); -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
