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?
} netif_stop_queue(dev); grcan_stop_hardware(dev);
Regards, Oliver
