Re: [PATCH 1/3] mt76: mt7921s: fix the deadlock caused by sdio->stat_work

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> From: Sean Wang <sean.wang@mediatek.com>
> 
> Because wake_work and sdio->stat_work share the same workqueue mt76->wq,
> if sdio->stat_work cannot acquire the mutex lock such as that was possibly
> held up by mt7921_mutex_acquire, we should exit immediately and schedule
> another stat_work to avoid blocking the mt7921_mutex_acquire.
> 
> Also, if mt7921_mutex_acquire was called by sdio->stat_work self, the wake
> would be blocked by itself, so we have to changing into an unblocking wake
> (directly wakeup via mt7921_mcu_drv_pmctrl, not via the wake_work) in the
> context.

Hi Sean,

it seems to me we are missing some logic here (e.g cancelling ps_work as we do
in mt76_connac_pm_wake()). Is it enough to move mt7921_usb_sdio_tx_status_data
on mac80211 workqueue? Can you see any performance issue? (same for mt7663).

Regards,
Lorenzo

> 
> Fixes: 48fab5bbef40 ("mt76: mt7921: introduce mt7921s support")
> Co-developed-by: YN Chen <YN.Chen@mediatek.com>
> Signed-off-by: YN Chen <YN.Chen@mediatek.com>
> Signed-off-by: Sean Wang <sean.wang@mediatek.com>
> ---
>  .../net/wireless/mediatek/mt76/mt7921/mac.c   | 22 +++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/mediatek/mt76/mt7921/mac.c b/drivers/net/wireless/mediatek/mt76/mt7921/mac.c
> index 6bd9fc9228a2..75e719175e92 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt7921/mac.c
> +++ b/drivers/net/wireless/mediatek/mt76/mt7921/mac.c
> @@ -1080,10 +1080,28 @@ bool mt7921_usb_sdio_tx_status_data(struct mt76_dev *mdev, u8 *update)
>  {
>  	struct mt7921_dev *dev = container_of(mdev, struct mt7921_dev, mt76);
>  
> -	mt7921_mutex_acquire(dev);
> +	if (!mutex_trylock(&mdev->mutex)) {
> +		/* Because wake_work and stat_work share the same workqueue
> +		 * mt76->wq, if sdio->stat_work cannot acquire the mutex lock,
> +		 * we should exit immediately and schedule another stat_work
> +		 * to avoid blocking the wake_work.
> +		 */
> +		struct work_struct *stat_work;
> +
> +		stat_work = mt76_is_sdio(mdev) ? &mdev->sdio.stat_work :
> +			    &mdev->usb.stat_work;
> +		queue_work(dev->mt76.wq, stat_work);
> +
> +		goto out;
> +	}
> +
> +	mt7921_mcu_drv_pmctrl(dev);
>  	mt7921_mac_sta_poll(dev);
> -	mt7921_mutex_release(dev);
> +	mt76_connac_power_save_sched(&mdev->phy, &dev->pm);
>  
> +	mutex_unlock(&mdev->mutex);
> +
> +out:
>  	return false;
>  }
>  EXPORT_SYMBOL_GPL(mt7921_usb_sdio_tx_status_data);
> -- 
> 2.25.1
> 

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