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@xxxxxxxxxxxxxxxxxx>
CCing the driver author...
> ---
> drivers/net/can/rcar/rcar_canfd.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/can/rcar/rcar_canfd.c b/drivers/net/can/rcar/rcar_canfd.c
> index 05410008aa6b..de34a4b82d4a 100644
> --- a/drivers/net/can/rcar/rcar_canfd.c
> +++ b/drivers/net/can/rcar/rcar_canfd.c
> @@ -1508,10 +1508,11 @@ static int rcar_canfd_rx_poll(struct napi_struct *napi, int quota)
>
> /* All packets processed */
> if (num_pkts < quota) {
> - napi_complete_done(napi, num_pkts);
> - /* Enable Rx FIFO interrupts */
> - rcar_canfd_set_bit(priv->base, RCANFD_RFCC(ridx),
> - RCANFD_RFCC_RFIE);
> + if (napi_complete_done(napi, num_pkts)) {
> + /* Enable Rx FIFO interrupts */
> + rcar_canfd_set_bit(priv->base, RCANFD_RFCC(ridx),
> + RCANFD_RFCC_RFIE);
> + }
> }
> return num_pkts;
> }
> --
> 2.11.0
>
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