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| author | Al Viro <viro@zeniv.linux.org.uk> | 2014-06-12 00:29:13 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-03-03 15:06:46 -0800 |
| commit | 4d57edcd044c0a5e0ae5241ec51962f5219caee2 (patch) | |
| tree | 03e9064ec4b8dcaebee2d529b4798349ccdadf91 /fs | |
| parent | 001869c34bdefa35f021f2633ed37122cfd3aa2d (diff) | |
| download | lwn-4d57edcd044c0a5e0ae5241ec51962f5219caee2.tar.gz lwn-4d57edcd044c0a5e0ae5241ec51962f5219caee2.zip | |
lock_parent: don't step on stale ->d_parent of all-but-freed one
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 <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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 40d474129c1c..9b235362efcd 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -530,10 +530,12 @@ 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); |