[ 010/108] vfs: dcache: use DCACHE_DENTRY_KILLED instead of DCACHE_DISCONNECTED in d_kill()

Ben Hutchings
2012-10-07T23:22:16Z

From: Miklos Szeredi <mszeredi@suse.cz>

commit b161dfa6937ae46d50adce8a7c6b12233e96e7bd upstream.

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 <mszeredi@suse.cz>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/dcache.c | 4 ++--
include/linux/dcache.h | 2 ++
2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 8086636..16521a9 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;
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index caa34e5..5920079 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -206,6 +206,8 @@ struct dentry_operations {
#define DCACHE_MANAGED_DENTRY \
(DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)

+#define DCACHE_DENTRY_KILLED 0x100000
+
extern seqlock_t rename_lock;

static inline int dname_external(struct dentry *dentry)