From: Jeff Layton jlayton@kernel.org
[ Upstream commit dc3da0461cc4b76f2d0c5b12247fcb3b520edbbf ]
Nothing ensures that session will still be valid by the time we dereference the pointer. Take and put a reference.
In principle, we should always be able to get a reference here, but throw a warning if that's ever not the case.
Signed-off-by: Jeff Layton jlayton@kernel.org Signed-off-by: Ilya Dryomov idryomov@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/ceph/caps.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c index 3d0497421e62b..49e693232916f 100644 --- a/fs/ceph/caps.c +++ b/fs/ceph/caps.c @@ -1777,12 +1777,24 @@ ack: if (mutex_trylock(&session->s_mutex) == 0) { dout("inverting session/ino locks on %p\n", session); + session = ceph_get_mds_session(session); spin_unlock(&ci->i_ceph_lock); if (took_snap_rwsem) { up_read(&mdsc->snap_rwsem); took_snap_rwsem = 0; } - mutex_lock(&session->s_mutex); + if (session) { + mutex_lock(&session->s_mutex); + ceph_put_mds_session(session); + } else { + /* + * Because we take the reference while + * holding the i_ceph_lock, it should + * never be NULL. Throw a warning if it + * ever is. + */ + WARN_ON_ONCE(true); + } goto retry; } }