[PATCH 4.14 29/68] net/ncsi: Avoid channel_monitor hrtimer deadlock

Greg Kroah-Hartman
2021-04-15T15:05:07Z

From: Milton Miller <miltonm@us.ibm.com>

[ Upstream commit 03cb4d05b4ea9a3491674ca40952adb708d549fa ]

Calling ncsi_stop_channel_monitor from channel_monitor is a guaranteed
deadlock on SMP because stop calls del_timer_sync on the timer that
invoked channel_monitor as its timer function.

Recognise the inherent race of marking the monitor disabled before
deleting the timer by just returning if enable was cleared. After
a timeout (the default case -- reset to START when response received)
just mark the monitor.enabled false.

If the channel has an entry on the channel_queue list, or if the
state is not ACTIVE or INACTIVE, then warn and mark the timer stopped
and don't restart, as the locking is broken somehow.

Fixes: 0795fb2021f0 ("net/ncsi: Stop monitor if channel times out or is inactive")
Signed-off-by: Milton Miller <miltonm@us.ibm.com>
Signed-off-by: Eddie James <eajames@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ncsi/ncsi-manage.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/net/ncsi/ncsi-manage.c b/net/ncsi/ncsi-manage.c
index 28c42b22b748..6b7f9e1f64d3 100644
--- a/net/ncsi/ncsi-manage.c
+++ b/net/ncsi/ncsi-manage.c
@@ -203,13 +203,20 @@ static void ncsi_channel_monitor(unsigned long data)
monitor_state = nc->monitor.state;
spin_unlock_irqrestore(&nc->lock, flags);

- if (!enabled || chained) {
- ncsi_stop_channel_monitor(nc);
- return;
- }
+ if (!enabled)
+ return; /* expected race disabling timer */
+ if (WARN_ON_ONCE(chained))
+ goto bad_state;
+
if (state != NCSI_CHANNEL_INACTIVE &&
state != NCSI_CHANNEL_ACTIVE) {
- ncsi_stop_channel_monitor(nc);
+bad_state:
+ netdev_warn(ndp->ndev.dev,
+ "Bad NCSI monitor state channel %d 0x%x %s queue\n",
+ nc->id, state, chained ? "on" : "off");
+ spin_lock_irqsave(&nc->lock, flags);
+ nc->monitor.enabled = false;
+ spin_unlock_irqrestore(&nc->lock, flags);
return;
}

@@ -234,10 +241,9 @@ static void ncsi_channel_monitor(unsigned long data)
ndp->flags |= NCSI_DEV_RESHUFFLE;
}

- ncsi_stop_channel_monitor(nc);
-
ncm = &nc->modes[NCSI_MODE_LINK];
spin_lock_irqsave(&nc->lock, flags);
+ nc->monitor.enabled = false;
nc->state = NCSI_CHANNEL_INVISIBLE;
ncm->data[2] &= ~0x1;
spin_unlock_irqrestore(&nc->lock, flags);
--
2.30.2