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| author | Al Viro <viro@zeniv.linux.org.uk> | 2014-06-12 00:29:13 -0400 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2014-06-12 00:29:13 -0400 |
| commit | c2338f2dc7c1e9f6202f370c64ffd7f44f3d4b51 (patch) | |
| tree | 54677cd1be2c934fea684a53e34f85d4c6f4981e /fs | |
| parent | 9c1d5284c79fea050f115eadeec1dd1758e5c630 (diff) | |
| download | lwn-c2338f2dc7c1e9f6202f370c64ffd7f44f3d4b51.tar.gz lwn-c2338f2dc7c1e9f6202f370c64ffd7f44f3d4b51.zip | |
lock_parent: don't step on stale ->d_parent of all-but-freed one
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 <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/dcache.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index be2bea834bf4..e99c6f529ba8 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -532,10 +532,12 @@ 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); |