From 13f172ff26563995049abe73f6eeba828de3c09d Mon Sep 17 00:00:00 2001 From: Neil Horman Date: Fri, 22 Apr 2011 08:10:59 +0000 Subject: [PATCH] netconsole: fix deadlock when removing net driver that netconsole is using (v2) A deadlock was reported to me recently that occured when netconsole was being used in a virtual guest. If the virtio_net driver was removed while netconsole was setup to use an interface that was driven by that driver, the guest deadlocked. No backtrace was provided because netconsole was the only console configured, but it became clear pretty quickly what the problem was. In netconsole_netdev_event, if we get an unregister event, we call __netpoll_cleanup with the target_list_lock held and irqs disabled. __netpoll_cleanup can, if pending netpoll packets are waiting call cancel_delayed_work_sync, which is a sleeping path. the might_sleep call in that path gets triggered, causing a console warning to be issued. The netconsole write handler of course tries to take the target_list_lock again, which we already hold, causing deadlock. The fix is pretty striaghtforward. Simply drop the target_list_lock and re-enable irqs prior to calling __netpoll_cleanup, the re-acquire the lock, and restart the loop. Confirmed by myself to fix the problem reported. Signed-off-by: Neil Horman CC: "David S. Miller" Signed-off-by: David S. Miller --- drivers/net/netconsole.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c index dfb67eb2a94b..eb41e44921e6 100644 --- a/drivers/net/netconsole.c +++ b/drivers/net/netconsole.c @@ -671,6 +671,7 @@ static int netconsole_netdev_event(struct notifier_block *this, goto done; spin_lock_irqsave(&target_list_lock, flags); +restart: list_for_each_entry(nt, &target_list, list) { netconsole_target_get(nt); if (nt->np.dev == dev) { @@ -683,9 +684,16 @@ static int netconsole_netdev_event(struct notifier_block *this, * rtnl_lock already held */ if (nt->np.dev) { + spin_unlock_irqrestore( + &target_list_lock, + flags); __netpoll_cleanup(&nt->np); + spin_lock_irqsave(&target_list_lock, + flags); dev_put(nt->np.dev); nt->np.dev = NULL; + netconsole_target_put(nt); + goto restart; } /* Fall through */ case NETDEV_GOING_DOWN: -- GitLab