Lorenzo Bianconi <lorenzo@xxxxxxxxxx> writes:
> Fix a possible race in mt7921_pm_power_save_work() if rx/tx napi
> schedules ps_work and we are currently accessing device register
> on a different cpu.
>
> Fixes: 1d8efc741df8 ("mt76: mt7921: introduce Runtime PM support")
> Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
> ---
> drivers/net/wireless/mediatek/mt76/mt7921/mac.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/net/wireless/mediatek/mt76/mt7921/mac.c b/drivers/net/wireless/mediatek/mt76/mt7921/mac.c
> index defef3496246..0744f6e42ba3 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt7921/mac.c
> +++ b/drivers/net/wireless/mediatek/mt76/mt7921/mac.c
> @@ -1553,6 +1553,14 @@ void mt7921_pm_power_save_work(struct work_struct *work)
> dev->fw_assert)
> goto out;
>
> + if (mutex_is_locked(&dev->mt76.mutex))
> + /* if mt76 mutex is held we should not put the device
> + * to sleep since we are currently accessing device
> + * register map. We need to wait for the next power_save
> + * trigger.
> + */
> + goto out;
This looks fishy to me. What protects the case when ps_work is run first
and at the same time another cpu starts accessing the registers?
Do note that I didn't check the code, so I might be missing something.
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