On 11/16/23 5:43 AM, Yoshihiro Shimoda wrote:
[...]
>>> Fix races between ravb_tx_timeout_work() and functions of net_device_ops
>>> and ethtool_ops by using rtnl_trylock() and rtnl_unlock(). Note that
>>> since ravb_close() is under the rtnl lock and calls cancel_work_sync(),
>>> ravb_tx_timeout_work() should calls rtnl_trylock(). Otherwise, a deadlock
>>> may happen in ravb_tx_timeout_work() like below:
>>>
>>> CPU0 CPU1
>>> ravb_tx_timeout()
>>> schedule_work()
>>> ...
>>> __dev_close_many()
>>> // Under rtnl lock
>>> ravb_close()
>>> cancel_work_sync()
>>> // Waiting
>>> ravb_tx_timeout_work()
>>> rtnl_lock()
>>> // This is possible to cause a deadlock
>>>
>>> And, if rtnl_trylock() fails and the netif is still running,
>>> rescheduling the work with 1 msec delayed. So, using
Ah, you say 1 ms here but 10 ms in the code! Not good... :-)
>>> schedule_delayed_work() instead of schedule_work().
>>>
>>> Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
>>> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
>>> Reviewed-by: Sergey Shtylyov <s.shtylyov@xxxxxx>
>>
>> Hm, I haven't reviewed this version... :-)
>
> Oops, I should have dropped the tag...
>
>>> Reviewed-by: Simon Horman <horms@xxxxxxxxxx>
>> [...]
>>> diff --git a/drivers/net/ethernet/renesas/ravb.h b/drivers/net/ethernet/renesas/ravb.h
>>> index e0f8276cffed..e9bb8ee3ba2d 100644
>>> --- a/drivers/net/ethernet/renesas/ravb.h
>>> +++ b/drivers/net/ethernet/renesas/ravb.h
>>> @@ -1081,7 +1081,7 @@ struct ravb_private {
>>> u32 cur_tx[NUM_TX_QUEUE];
>>> u32 dirty_tx[NUM_TX_QUEUE];
>>> struct napi_struct napi[NUM_RX_QUEUE];
>>> - struct work_struct work;
>>> + struct delayed_work work;
>>
>> Not sure this is justified...
>> Then again, what do I know about workqueues? Not much... :-)
>
> I thought that the schedule_work() called the work function immediately.
> So, I thought call*ing the schedule_work() from the work function caused
> endless loop. However, it is not true. The schedule_work() just inserts
> a work queue, and then the kernel calls the work function later.
>
> So, changing from work_struct to delayed_work is not needed for fixing
> this issue, I think now. However, I have another concern about rescheduling
> this work by schedule_work() here because it's possible to cause high CPU load
> while the rtnl_lock() is held. So, I think we should call a sleep function
> like usleep_range(1000, 2000) for instance before schedule_work().
> But, what do you think?
I think that a sleep before requeuing is pretty much the same as using
a delayed work...
>> [...]
>>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
>>> index c70cff80cc99..ca7db8a5b412 100644
>>> --- a/drivers/net/ethernet/renesas/ravb_main.c
>>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
>>> @@ -1863,17 +1863,24 @@ static void ravb_tx_timeout(struct net_device *ndev, unsigned int txqueue)
>>> /* tx_errors count up */
>>> ndev->stats.tx_errors++;
>>>
>>> - schedule_work(&priv->work);
>>> + schedule_delayed_work(&priv->work, 0);
>>> }
>>>
>>> static void ravb_tx_timeout_work(struct work_struct *work)
>>> {
>>> - struct ravb_private *priv = container_of(work, struct ravb_private,
>>> + struct delayed_work *dwork = to_delayed_work(work);
>>> + struct ravb_private *priv = container_of(dwork, struct ravb_private,
>>> work);
>>> const struct ravb_hw_info *info = priv->info;
>>> struct net_device *ndev = priv->ndev;
>>> int error;
>>>
>>> + if (!rtnl_trylock()) {
>>> + if (netif_running(ndev))
>>> + schedule_delayed_work(&priv->work, msecs_to_jiffies(10));
You could reuse dwork instead of &priv->work here...
>> The delay is rather arbitrary. Why not e.g. 1 ms?
>
> I think that 1 ms is enough.
Seeing now that 1 ms was intended...
> Best regards,
> Yoshihiro Shimoda
[...]
MBR, Sergey
