6.6-stable review patch. If anyone has any objections, please let me know.
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From: Henrique Carvalho henrique.carvalho@suse.com
commit a9d1f38df7ecd0e21233447c9cc6fa1799eddaf3 upstream.
Replace close_cached_dir() calls under cfid_list_lock with a new close_cached_dir_locked() variant that uses kref_put() instead of kref_put_lock() to avoid recursive locking when dropping references.
While the existing code works if the refcount >= 2 invariant holds, this area has proven error-prone. Make deadlocks impossible and WARN on invariant violations.
Cc: stable@vger.kernel.org Reviewed-by: David Howells dhowells@redhat.com Signed-off-by: Henrique Carvalho henrique.carvalho@suse.com Signed-off-by: Steve French stfrench@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/smb/client/cached_dir.c | 41 ++++++++++++++++++++++++++++++++++++++--- 1 file changed, 38 insertions(+), 3 deletions(-)
--- a/fs/smb/client/cached_dir.c +++ b/fs/smb/client/cached_dir.c @@ -16,6 +16,7 @@ static struct cached_fid *init_cached_di static void free_cached_dir(struct cached_fid *cfid); static void smb2_close_cached_fid(struct kref *ref); static void cfids_laundromat_worker(struct work_struct *work); +static void close_cached_dir_locked(struct cached_fid *cfid);
struct cached_dir_dentry { struct list_head entry; @@ -362,7 +363,7 @@ out: * lease. Release one here, and the second below. */ cfid->has_lease = false; - close_cached_dir(cfid); + close_cached_dir_locked(cfid); } spin_unlock(&cfids->cfid_list_lock);
@@ -448,18 +449,52 @@ void drop_cached_dir_by_name(const unsig spin_lock(&cfid->cfids->cfid_list_lock); if (cfid->has_lease) { cfid->has_lease = false; - close_cached_dir(cfid); + close_cached_dir_locked(cfid); } spin_unlock(&cfid->cfids->cfid_list_lock); close_cached_dir(cfid); }
- +/** + * close_cached_dir - drop a reference of a cached dir + * + * The release function will be called with cfid_list_lock held to remove the + * cached dirs from the list before any other thread can take another @cfid + * ref. Must not be called with cfid_list_lock held; use + * close_cached_dir_locked() called instead. + * + * @cfid: cached dir + */ void close_cached_dir(struct cached_fid *cfid) { + lockdep_assert_not_held(&cfid->cfids->cfid_list_lock); kref_put_lock(&cfid->refcount, smb2_close_cached_fid, &cfid->cfids->cfid_list_lock); }
+/** + * close_cached_dir_locked - put a reference of a cached dir with + * cfid_list_lock held + * + * Calling close_cached_dir() with cfid_list_lock held has the potential effect + * of causing a deadlock if the invariant of refcount >= 2 is false. + * + * This function is used in paths that hold cfid_list_lock and expect at least + * two references. If that invariant is violated, WARNs and returns without + * dropping a reference; the final put must still go through + * close_cached_dir(). + * + * @cfid: cached dir + */ +static void close_cached_dir_locked(struct cached_fid *cfid) +{ + lockdep_assert_held(&cfid->cfids->cfid_list_lock); + + if (WARN_ON(kref_read(&cfid->refcount) < 2)) + return; + + kref_put(&cfid->refcount, smb2_close_cached_fid); +} + /* * Called from cifs_kill_sb when we unmount a share */