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ceph: fix potential race in ceph_check_caps

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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>
This commit is contained in:
Jeff Layton 2020-03-20 16:45:45 -04:00 committed by Ilya Dryomov
parent 4fb5dda39c
commit dc3da0461c
1 changed files with 13 additions and 1 deletions
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14
fs/ceph/caps.c
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@ -2044,12 +2044,24 @@ 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;
}
}