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From: Jose Abreu <Jose.Abreu@synopsys.com>
To: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	Joao Pinto <Joao.Pinto@synopsys.com>
Subject: stmmac: Race in coalesce timer and NAPI
Date: Fri, 21 Sep 2018 10:19:45 +0100	[thread overview]
Message-ID: <dd4b67f1-5ce7-22e2-8fe5-8925ec016386@synopsys.com> (raw)

Hello,

I'm getting a race in stmmac coalesce timer and the
napi_schedule() interrupt and I'm asking for advice. Currently,
we are scheduling NAPI in coalesce timer but this leads to
stmmac_tx_clean() deadlock because this function tries to acquire
queue lock.

I find that this is not expected because only one instance of
NAPI should run at same time so I was wondering if it is possible
that xmit() callback is causing the deadlock ?

BTW, this is solved by:
    - Directly call stmmac_tx_clean() in timer function AND
    - Use netif_tx_trylock() in stmmac_tx_clean(). Then, if queue
is already locked we re-arm coalesce timer or reschedule NAPI.

This is easily reproducible in an ARM board with 8 core running
at 100MHz each.

Thanks and Best Regards,
Jose Miguel Abreu

             reply	other threads:[~2018-09-21 15:07 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-21  9:19 Jose Abreu [this message]
2018-09-21 13:54 ` stmmac: Race in coalesce timer and NAPI Eric Dumazet

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