[PATCH AUTOSEL for 4.4 014/167] lockd: fix lockd shutdown race

Sasha Levin
2018-03-19T16:06:59Z

From: "J. Bruce Fields" <bfields@redhat.com>

[ Upstream commit efda760fe95ea15291853c8fa9235c32d319cd98 ]

As reported by David Jeffery: "a signal was sent to lockd while lockd
was shutting down from a request to stop nfs. The signal causes lockd
to call restart_grace() which puts the lockd_net structure on the grace
list. If this signal is received at the wrong time, it will occur after
lockd_down_net() has called locks_end_grace() but before
lockd_down_net() stops the lockd thread. This leads to lockd putting
the lockd_net structure back on the grace list, then exiting without
anything removing it from the list."

So, perform the final locks_end_grace() from the the lockd thread; this
ensures it's serialized with respect to restart_grace().

Reported-by: David Jeffery <djeffery@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
fs/lockd/svc.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index 5f31ebd96c06..a2edb0049eb5 100644
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -129,6 +129,8 @@ lockd(void *vrqstp)
{
int err = 0;
struct svc_rqst *rqstp = vrqstp;
+ struct net *net = &init_net;
+ struct lockd_net *ln = net_generic(net, lockd_net_id);

/* try_to_freeze() is called from svc_recv() */
set_freezable();
@@ -173,6 +175,8 @@ lockd(void *vrqstp)
if (nlmsvc_ops)
nlmsvc_invalidate_all();
nlm_shutdown_hosts();
+ cancel_delayed_work_sync(&ln->grace_period_end);
+ locks_end_grace(&ln->lockd_manager);
return 0;
}

@@ -267,8 +271,6 @@ static void lockd_down_net(struct svc_serv *serv, struct net *net)
if (ln->nlmsvc_users) {
if (--ln->nlmsvc_users == 0) {
nlm_shutdown_hosts_net(net);
- cancel_delayed_work_sync(&ln->grace_period_end);
- locks_end_grace(&ln->lockd_manager);
svc_shutdown_net(serv, net);
dprintk("lockd_down_net: per-net data destroyed; net=%p\n", net);
}
--
2.14.1