linux-kernel - Re: [PATCH resend] can: rcar_canfd: fix possible IRQ storm on high load

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Date:   Wed, 26 Jun 2019 15:32:20 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Nikita Yushchenko <nikita.yoush@...entembedded.com>
Cc:     Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        Simon Horman <horms+renesas@...ge.net.au>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Artemi Ivanov <artemi.ivanov@...entembedded.com>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Subject: Re: [PATCH resend] can: rcar_canfd: fix possible IRQ storm on high
 load

On Wed, Jun 26, 2019 at 03:12:51PM +0200, Wolfram Sang wrote:
> On Wed, Jun 26, 2019 at 04:08:48PM +0300, Nikita Yushchenko wrote:
> > We have observed rcar_canfd driver entering IRQ storm under high load,
> > with following scenario:
> > - rcar_canfd_global_interrupt() in entered due to Rx available,
> > - napi_schedule_prep() is called, and sets NAPIF_STATE_SCHED in state
> > - Rx fifo interrupts are masked,
> > - rcar_canfd_global_interrupt() is entered again, this time due to
> >   error interrupt (e.g. due to overflow),
> > - since scheduled napi poller has not yet executed, condition for calling
> >   napi_schedule_prep() from rcar_canfd_global_interrupt() remains true,
> >   thus napi_schedule_prep() gets called and sets NAPIF_STATE_MISSED flag
> >   in state,
> > - later, napi poller function rcar_canfd_rx_poll() gets executed, and
> >   calls napi_complete_done(),
> > - due to NAPIF_STATE_MISSED flag in state, this call does not clear
> >   NAPIF_STATE_SCHED flag from state,
> > - on return from napi_complete_done(), rcar_canfd_rx_poll() unmasks Rx
> >   interrutps,
> > - Rx interrupt happens, rcar_canfd_global_interrupt() gets called
> >   and calls napi_schedule_prep(),
> > - since NAPIF_STATE_SCHED is set in state at this time, this call
> >   returns false,
> > - due to that false return, rcar_canfd_global_interrupt() returns
> >   without masking Rx interrupt
> > - and this results into IRQ storm: unmasked Rx interrupt happens again
> >   and again is misprocessed in the same way.
> > 
> > This patch fixes that scenario by unmasking Rx interrupts only when
> > napi_complete_done() returns true, which means it has cleared
> > NAPIF_STATE_SCHED in state.
> > 
> > Signed-off-by: Nikita Yushchenko <nikita.yoush@...entembedded.com>
> 
> CCing the driver author...

Bounced :(


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