From: Al Viro <v...@zeniv.linux.org.uk>
This patch has been added to the 3.12 stable tree. If you have any
objections, please let us know.
===============
commit c2338f2dc7c1e9f6202f370c64ffd7f44f3d4b51 upstream.
Dentry that had been through (or into) __dentry_kill() might be seen
by shrink_dentry_list(); that's normal, it'll be taken off the shrink
list and freed if __dentry_kill() has already finished. The problem
is, its ->d_parent might be pointing to already freed dentry, so
lock_parent() needs to be careful.
We need to check that dentry hasn't already gone into __dentry_kill()
*and* grab rcu_read_lock() before dropping ->d_lock - the latter makes
sure that whatever we see in ->d_parent after dropping ->d_lock it
won't be freed until we drop rcu_read_lock().
Signed-off-by: Al Viro <v...@zeniv.linux.org.uk>
Signed-off-by: Jiri Slaby <jsl...@suse.cz>
---
fs/dcache.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 85bc01f4bbca..e15f90c0e96a 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -554,10 +554,12 @@ static inline struct dentry *lock_parent(struct dentry
*dentry)
struct dentry *parent = dentry->d_parent;
if (IS_ROOT(dentry))
return NULL;
+ if (unlikely((int)dentry->d_lockref.count < 0))
+ return NULL;
if (likely(spin_trylock(&parent->d_lock)))
return parent;
- spin_unlock(&dentry->d_lock);
rcu_read_lock();
+ spin_unlock(&dentry->d_lock);
again:
parent = ACCESS_ONCE(dentry->d_parent);
spin_lock(&parent->d_lock);
--
2.1.2
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