The commit is pushed to "branch-rh7-3.10.0-1160.11.1.vz7.172.x-ovz" and will
appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.11.1.vz7.172.13
------>
commit d8fcddcb834f35d3655e41e7ad0c25f93d8b9485
Author: Al Viro <[email protected]>
Date: Wed Feb 17 15:36:08 2021 +0300
ms/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 <[email protected]>
(cherry picked from commit c2338f2dc7c1e9f6202f370c64ffd7f44f3d4b51)
Signed-off-by: Vasily Averin <[email protected]>
---
fs/dcache.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 41e8f55..3d6b9b4 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -701,10 +701,12 @@ 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);
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