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Fix deadlock in netconsoles netdev notifier handler function

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Resolves: bz 668231
This commit is contained in:
Neil Horman 2011-04-25 12:04:09 -04:00
commit cb4a4c8907
2 changed files with 65 additions and 0 deletions
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9
kernel.spec
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@ -726,6 +726,9 @@ Patch12306: scsi-sd-downgrade-caching-printk-from-error-to-notice.patch
Patch12307: iwlwifi-do-not-set-tx-power-when-channel-is-changing.patch
#netconsole fixes
Patch12400: linux-2.6-netconsole-deadlock.patch
%endif
BuildRoot: %{_tmppath}/kernel-%{KVERREL}-root
@ -1348,6 +1351,9 @@ ApplyPatch printk-do-not-mangle-valid-userspace-syslog-prefixes.patch
ApplyPatch scsi-sd-downgrade-caching-printk-from-error-to-notice.patch
#rhbz 668231
ApplyPatch linux-2.6-netconsole-deadlock.patch
# END OF PATCH APPLICATIONS
%endif
@ -1956,6 +1962,9 @@ fi
# and build.
%changelog
* Mon Apr 25 2011 Neil Horman <nhorman@redhat.com>
- netconsole: fix deadlock in netdev notifier handler
* Sun Apr 24 2011 Kyle McMartin <kmcmartin@redhat.com>
- ppc64: disable TUNE_CELL, which causes problems with illegal instuctions
being generated on non-Cell PPC machines. (#698256)

56
linux-2.6-netconsole-deadlock.patch Normal file
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@ -0,0 +1,56 @@
commit 13f172ff26563995049abe73f6eeba828de3c09d
Author: Neil Horman <nhorman@tuxdriver.com>
Date: Fri Apr 22 08:10:59 2011 +0000
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 <nhorman@tuxdriver.com>
CC: "David S. Miller" <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index dfb67eb..eb41e44 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: