From b161dfa6937ae46d50adce8a7c6b12233e96e7bd Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Mon, 17 Sep 2012 22:31:38 +0200 Subject: vfs: dcache: use DCACHE_DENTRY_KILLED instead of DCACHE_DISCONNECTED in d_kill() IBM reported a soft lockup after applying the fix for the rename_lock deadlock. Commit c83ce989cb5f ("VFS: Fix the nfs sillyrename regression in kernel 2.6.38") was found to be the culprit. The nfs sillyrename fix used DCACHE_DISCONNECTED to indicate that the dentry was killed. This flag can be set on non-killed dentries too, which results in infinite retries when trying to traverse the dentry tree. This patch introduces a separate flag: DCACHE_DENTRY_KILLED, which is only set in d_kill() and makes try_to_ascend() test only this flag. IBM reported successful test results with this patch. Signed-off-by: Miklos Szeredi Cc: Trond Myklebust Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds --- fs/dcache.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'fs/dcache.c') diff --git a/fs/dcache.c b/fs/dcache.c index 8086636bf79..16521a9f203 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -389,7 +389,7 @@ static struct dentry *d_kill(struct dentry *dentry, struct dentry *parent) * Inform try_to_ascend() that we are no longer attached to the * dentry tree */ - dentry->d_flags |= DCACHE_DISCONNECTED; + dentry->d_flags |= DCACHE_DENTRY_KILLED; if (parent) spin_unlock(&parent->d_lock); dentry_iput(dentry); @@ -1048,7 +1048,7 @@ static struct dentry *try_to_ascend(struct dentry *old, int locked, unsigned seq * or deletion */ if (new != old->d_parent || - (old->d_flags & DCACHE_DISCONNECTED) || + (old->d_flags & DCACHE_DENTRY_KILLED) || (!locked && read_seqretry(&rename_lock, seq))) { spin_unlock(&new->d_lock); new = NULL; -- cgit v1.2.3-70-g09d2 From fd51790949edbbd17633689d4e19fe26d8447764 Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" Date: Tue, 18 Sep 2012 16:35:51 -0400 Subject: trivial select_parent documentation fix "Search list for X" sounds like you're trying to find X on a list. Signed-off-by: J. Bruce Fields Signed-off-by: Linus Torvalds --- fs/dcache.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/dcache.c') diff --git a/fs/dcache.c b/fs/dcache.c index 16521a9f203..0364af2311f 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1141,7 +1141,7 @@ rename_retry: EXPORT_SYMBOL(have_submounts); /* - * Search the dentry child list for the specified parent, + * Search the dentry child list of the specified parent, * and move any unused dentries to the end of the unused * list for prune_dcache(). We descend to the next level * whenever the d_subdirs list is non-empty and continue -- cgit v1.2.3-70-g09d2 From 8110e16d42d587997bcaee0c864179e6d93603fe Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Mon, 17 Sep 2012 22:23:30 +0200 Subject: vfs: dcache: fix deadlock in tree traversal IBM reported a deadlock in select_parent(). This was found to be caused by taking rename_lock when already locked when restarting the tree traversal. There are two cases when the traversal needs to be restarted: 1) concurrent d_move(); this can only happen when not already locked, since taking rename_lock protects against concurrent d_move(). 2) racing with final d_put() on child just at the moment of ascending to parent; rename_lock doesn't protect against this rare race, so it can happen when already locked. Because of case 2, we need to be able to handle restarting the traversal when rename_lock is already held. This patch fixes all three callers of try_to_ascend(). IBM reported that the deadlock is gone with this patch. [ I rewrote the patch to be smaller and just do the "goto again" if the lock was already held, but credit goes to Miklos for the real work. - Linus ] Signed-off-by: Miklos Szeredi Cc: Al Viro Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds --- fs/dcache.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'fs/dcache.c') diff --git a/fs/dcache.c b/fs/dcache.c index 0364af2311f..693f95bf1ca 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1134,6 +1134,8 @@ positive: return 1; rename_retry: + if (locked) + goto again; locked = 1; write_seqlock(&rename_lock); goto again; @@ -1236,6 +1238,8 @@ out: rename_retry: if (found) return found; + if (locked) + goto again; locked = 1; write_seqlock(&rename_lock); goto again; @@ -3035,6 +3039,8 @@ resume: return; rename_retry: + if (locked) + goto again; locked = 1; write_seqlock(&rename_lock); goto again; -- cgit v1.2.3-70-g09d2