On 2022-04-26 21:12, Oliver Hartkopp wrote:
On 25.04.22 06:24, Duoming Zhou wrote:
There are deadlocks caused by del_timer_sync(&priv->hang_timer)
and del_timer_sync(&priv->rr_timer) in grcan_close(), one of
the deadlocks are shown below:
(Thread 1) | (Thread 2)
| grcan_reset_timer()
grcan_close() | mod_timer()
spin_lock_irqsave() //(1) | (wait a time)
... | grcan_initiate_running_reset()
del_timer_sync() | spin_lock_irqsave() //(2)
(wait timer to stop) | ...
We hold priv->lock in position (1) of thread 1 and use
del_timer_sync() to wait timer to stop, but timer handler
also need priv->lock in position (2) of thread 2.
As a result, grcan_close() will block forever.
This patch extracts del_timer_sync() from the protection of
spin_lock_irqsave(), which could let timer handler to obtain
the needed lock.
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
drivers/net/can/grcan.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/net/can/grcan.c b/drivers/net/can/grcan.c
index d0c5a7a60da..1189057b5d6 100644
--- a/drivers/net/can/grcan.c
+++ b/drivers/net/can/grcan.c
@@ -1102,8 +1102,10 @@ static int grcan_close(struct net_device *dev)
priv->closing = true;
if (priv->need_txbug_workaround) {
+ spin_unlock_irqrestore(&priv->lock, flags);
del_timer_sync(&priv->hang_timer);
del_timer_sync(&priv->rr_timer);
+ spin_lock_irqsave(&priv->lock, flags);
It looks weird to unlock and re-lock the operations like this. This
breaks the intended locking for the closing process.
Isn't there any possibility to e.g. move that entire if-section before
the lock?
All functions wishing to start the timers both check priv->closing and
then, if false, start the timer within the priv->lock spinlock. Given
that, it should be ok that del_timer_sync is not done within the
spinlock as therefore no one can restart any timers after priv->closing
has been set to true.
It looks a bit weird, but setting priv->closing to true needs to happen
within the priv->lock spinlock protection and needs to happen before
del_timer_sync to avoid a race between grcan_close and someone starting
the timer.
Reviewed-by: Andreas Larsson <andreas@xxxxxxxxxxx>
--
Andreas Larsson
