tree cfde0f75348706306314749a9ac8164d0237a0d4
parent cc8a55320b5f1196bee5bd14e4bb2ebd3b983317
author Jeff Layton <jlayton@poochiereds.net> 1443704750 -0400
committer J. Bruce Fields <bfields@redhat.com> 1445630253 -0400

nfsd: ensure that seqid morphing operations are atomic wrt to copies

Bruce points out that the increment of the seqid in stateids is not
serialized in any way, so it's possible for racing calls to bump it
twice and end up sending the same stateid. While we don't have any
reports of this problem it _is_ theoretically possible, and could lead
to spurious state recovery by the client.

In the current code, update_stateid is always followed by a memcpy of
that stateid, so we can combine the two operations. For better
atomicity, we add a spinlock to the nfs4_stid and hold that when bumping
the seqid and copying the stateid.

Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>