On Tue, Jul 22, 2014 at 01:52:06PM -0400, Jeff Layton wrote: > 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: Thanks, applying this version.--b. > > --------------------[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 -- 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
