Re: [PATCH v2 2/2] net: ethernet: stmmac: remove private tx queue lock
From: Lino Sanfilippo
Date: Thu Dec 15 2016 - 14:44:23 EST
Hi,
On 15.12.2016 10:45, Pavel Machek wrote:
> Hi!
>
>> The driver uses a private lock for synchronization of the xmit function and
>> the xmit completion handler, but since the NETIF_F_LLTX flag is not set,
>> the xmit function is also called with the xmit_lock held.
>>
>> On the other hand the completion handler uses the reverse locking order by
>> first taking the private lock and (in case that the tx queue had been
>> stopped) then the xmit_lock.
>>
>> Improve the locking by removing the private lock and using only the
>> xmit_lock for synchronization instead.
>
> Do you have stmmac hardware to test on?
>
Unfortunately not (I mentioned that the patch I send was only compile tested in
the first version but I think I forgot to do so in the last version).
> I believe something is very wrong with the locking there. In
> particular... scheduling the stmmac_tx_timer() function to run often
> should not do anything bad if locking is correct... but it breaks the
> driver rather quickly. [Example patch below, needs applying to two
> places in net-next.]
>
Do you get this result only after the private lock is removed? Or has this problem
been there before? And how exactly does the failure look like?
Regards,
Lino