diff options
| author | Alex Elder | 2012-01-29 13:57:43 -0600 |
|---|---|---|
| committer | Sage Weil | 2012-02-02 12:56:59 -0800 |
| commit | d23a4b3fd6ef70b80411b39b8c8bc548a219ce70 (patch) | |
| tree | f42dbc4c8544acce987e35df5b3002f1def54cff | |
| parent | 97bb59a03dd6767fcc00be09b0c6d9e5294eeea6 (diff) | |
rbd: fix safety of rbd_put_client()
The rbd_client structure uses a kref to arrange for cleaning up and
freeing an instance when its last reference is dropped. The cleanup
routine is rbd_client_release(), and one of the things it does is
delete the rbd_client from rbd_client_list. It acquires node_lock
to do so, but the way it is done is still not safe.
The problem is that when attempting to reuse an existing rbd_client,
the structure found might already be in the process of getting
destroyed and cleaned up.
Here's the scenario, with "CLIENT" representing an existing
rbd_client that's involved in the race:
Thread on CPU A | Thread on CPU B
--------------- | ---------------
rbd_put_client(CLIENT) | rbd_get_client()
kref_put() | (acquires node_lock)
kref->refcount becomes 0 | __rbd_client_find() returns CLIENT
calls rbd_client_release() | kref_get(&CLIENT->kref);
| (releases node_lock)
(acquires node_lock) |
deletes CLIENT from list | ...and starts using CLIENT...
(releases node_lock) |
and frees CLIENT | <-- but CLIENT gets freed here
Fix this by having rbd_put_client() acquire node_lock. The result
could still be improved, but at least it avoids this problem.
Signed-off-by: Alex Elder <elder@dreamhost.com>
Signed-off-by: Sage Weil <sage@newdream.net>
| -rw-r--r-- | drivers/block/rbd.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index 7d8f8ddb3359..7f40cb4553c9 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -407,15 +407,15 @@ done_err: /* * Destroy ceph client + * + * Caller must hold node_lock. */ static void rbd_client_release(struct kref *kref) { struct rbd_client *rbdc = container_of(kref, struct rbd_client, kref); dout("rbd_release_client %p\n", rbdc); - spin_lock(&node_lock); list_del(&rbdc->node); - spin_unlock(&node_lock); ceph_destroy_client(rbdc->client); kfree(rbdc->rbd_opts); @@ -428,7 +428,9 @@ static void rbd_client_release(struct kref *kref) */ static void rbd_put_client(struct rbd_device *rbd_dev) { + spin_lock(&node_lock); kref_put(&rbd_dev->rbd_client->kref, rbd_client_release); + spin_unlock(&node_lock); rbd_dev->rbd_client = NULL; rbd_dev->client = NULL; } |