Duoming Zhou <[email protected]> writes:
> If the work item is running, the cancel_work_sync in ar5523_stop will
> not return until work item is finished. If we hold mutex_lock and use
> cancel_work_sync to wait the work item to finish, the work item such as
> ar5523_tx_wd_work and ar5523_tx_work also require mutex_lock. As a result,
> the ar5523_stop will be blocked forever. One of the race conditions is
> shown below:
>
> (Thread 1) | (Thread 2)
> ar5523_stop |
> mutex_lock(&ar->mutex) | ar5523_tx_wd_work
> | mutex_lock(&ar->mutex)
> cancel_work_sync | ...
>
> This patch moves cancel_work_sync out of mutex_lock in order to mitigate
> deadlock bugs.
>
> Fixes: b7d572e1871d ("ar5523: Add new driver")
> Signed-off-by: Duoming Zhou <[email protected]>
I assume you have found this with a static checker tool, it would be
good document what tool you are using. And if you have not tested this
with real hardware clearly mention that with "Compile tested only".
> ---
> drivers/net/wireless/ath/ar5523/ar5523.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/wireless/ath/ar5523/ar5523.c b/drivers/net/wireless/ath/ar5523/ar5523.c
> index 9cabd342d15..99d6b13ffcf 100644
> --- a/drivers/net/wireless/ath/ar5523/ar5523.c
> +++ b/drivers/net/wireless/ath/ar5523/ar5523.c
> @@ -1071,8 +1071,10 @@ static void ar5523_stop(struct ieee80211_hw *hw)
> ar5523_cmd_write(ar, WDCMSG_TARGET_STOP, NULL, 0, 0);
>
> del_timer_sync(&ar->tx_wd_timer);
> + mutex_unlock(&ar->mutex);
> cancel_work_sync(&ar->tx_wd_work);
> cancel_work_sync(&ar->rx_refill_work);
> + mutex_lock(&ar->mutex);
> ar5523_cancel_rx_bufs(ar);
> mutex_unlock(&ar->mutex);
> }
Releasing a lock and taking it again looks like a hack to me. Please
test with a real device and try to find a better solution.
--
https://patchwork.kernel.org/project/linux-wireless/list/
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
Hello,
On Mon, 30 May 2022 14:24:04 +0300 Kalle Valo wrote:
> Duoming Zhou <[email protected]> writes:
>
> > If the work item is running, the cancel_work_sync in ar5523_stop will
> > not return until work item is finished. If we hold mutex_lock and use
> > cancel_work_sync to wait the work item to finish, the work item such as
> > ar5523_tx_wd_work and ar5523_tx_work also require mutex_lock. As a result,
> > the ar5523_stop will be blocked forever. One of the race conditions is
> > shown below:
> >
> > (Thread 1) | (Thread 2)
> > ar5523_stop |
> > mutex_lock(&ar->mutex) | ar5523_tx_wd_work
> > | mutex_lock(&ar->mutex)
> > cancel_work_sync | ...
> >
> > This patch moves cancel_work_sync out of mutex_lock in order to mitigate
> > deadlock bugs.
> >
> > Fixes: b7d572e1871d ("ar5523: Add new driver")
> > Signed-off-by: Duoming Zhou <[email protected]>
>
> I assume you have found this with a static checker tool, it would be
> good document what tool you are using. And if you have not tested this
> with real hardware clearly mention that with "Compile tested only".
>
> > ---
> > drivers/net/wireless/ath/ar5523/ar5523.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/net/wireless/ath/ar5523/ar5523.c b/drivers/net/wireless/ath/ar5523/ar5523.c
> > index 9cabd342d15..99d6b13ffcf 100644
> > --- a/drivers/net/wireless/ath/ar5523/ar5523.c
> > +++ b/drivers/net/wireless/ath/ar5523/ar5523.c
> > @@ -1071,8 +1071,10 @@ static void ar5523_stop(struct ieee80211_hw *hw)
> > ar5523_cmd_write(ar, WDCMSG_TARGET_STOP, NULL, 0, 0);
> >
> > del_timer_sync(&ar->tx_wd_timer);
> > + mutex_unlock(&ar->mutex);
> > cancel_work_sync(&ar->tx_wd_work);
> > cancel_work_sync(&ar->rx_refill_work);
> > + mutex_lock(&ar->mutex);
> > ar5523_cancel_rx_bufs(ar);
> > mutex_unlock(&ar->mutex);
> > }
>
> Releasing a lock and taking it again looks like a hack to me. Please
> test with a real device and try to find a better solution.
The following is a new solution:
diff --git a/drivers/net/wireless/ath/ar5523/ar5523.c b/drivers/net/wireless/ath/ar5523/ar5523.c
index 9cabd342d15..8adae85fcb9 100644
--- a/drivers/net/wireless/ath/ar5523/ar5523.c
+++ b/drivers/net/wireless/ath/ar5523/ar5523.c
@@ -910,7 +910,11 @@ static void ar5523_tx_wd_work(struct work_struct *work)
* recover seems to be to reset the dongle.
*/
- mutex_lock(&ar->mutex);
+ if(!mutex_trylock(&ar->mutex)) {
+ if(test_bit(AR5523_HW_UP, &ar->flags))
+ ieee80211_queue_work(ar->hw, &ar->tx_wd_work);
+ return;
+ }
ar5523_err(ar, "TX queue stuck (tot %d pend %d)\n",
atomic_read(&ar->tx_nr_total),
atomic_read(&ar->tx_nr_pending));
If ar5523_stop() has acquired "ar->mutex" lock, the ar5523_tx_wd_work() will directly return.
If "ar->mutex" lock has acquired by other functions except ar5523_stop(), ar5523_tx_wd_work()
will re-queue itself.
So, this solution could mitigate the deadlock between ar5523_stop() and ar5523_tx_wd_work().
Best regards,
Duoming Zhou