From: Eric Dumazet <edumazet@google.com>
To: Vlad Zakharov <Vladislav.Zakharov@synopsys.com>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"eladkan@mellanox.com" <eladkan@mellanox.com>,
"davem@davemloft.net" <davem@davemloft.net>,
"noamca@mellanox.com" <noamca@mellanox.com>,
"linux-snps-arc@lists.infradead.org"
<linux-snps-arc@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ezchip: nps_enet: check if napi has been completed
Date: Thu, 30 Mar 2017 06:25:47 -0700 [thread overview]
Message-ID: <CANn89iJysKbV92XW8UKb-YOmOqC=SSbz_urGDB4YubpdDYwYdA@mail.gmail.com> (raw)
In-Reply-To: <1490865403.32756.21.camel@synopsys.com>
On Thu, Mar 30, 2017 at 2:16 AM, Vlad Zakharov
<Vladislav.Zakharov@synopsys.com> wrote:
> I am not sure what is happening with other drivers, but in case of ezchip nps_enet driver after the following commit:
> 39e6c8208d7b6fb9d2047850fb3327db567b564b
>
> if we got into NAPI_STATE_MISSED state the following happened:
> in nps_enet_poll func we were calling napi_complete_done() (which reset MISSED state but left SCHED state) and after
> that without any checks were enabling interrupts.
>
> Then we obviously were getting into nps_enet_irq_hanlder() if irq was pending (it is very possbile state). If we look
> inside this function we will see that it disables interrupts only in case napi_sched_prep() returns true. In its turn
> napi_sched_prep() returns true only in case it changes state from non-SCHED to SCHED. But in our case as SCHED had been
> already set it set MISSED state and then returned false. So at that point we had already been trapped: after exiting irq
> hanlder we were getting into nps_enet_irq_hanlder() again and again as we couldn't rescind pending irq signal and
> disable corresponding irq.
Hi Vlad
Considering the use of napi_schedule_prep() in
nps_enet_irq_handler(), it is strange that nps_enet_poll() uses :
if (nps_enet_is_tx_pending(priv)) {
nps_enet_reg_set(priv, NPS_ENET_REG_BUF_INT_ENABLE, 0);
napi_reschedule(napi); // note the return value is ignored...
}
So nps_enet_poll() was enabling interrupts, then disabling them, which
seems very unusual.
I need to check all drivers using napi_schedule_prep() and/or
napi_reschedule() and make sure they also test napi_comple_done()
return value...
I count 12 drivers using napi_reschedule() without checking its return value.
They either should check its return value, or use conventional napi_schedule()
Thanks !
next prev parent reply other threads:[~2017-03-30 13:25 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-29 10:41 [PATCH] ezchip: nps_enet: check if napi has been completed Vlad Zakharov
2017-03-29 14:52 ` Eric Dumazet
2017-03-29 21:30 ` David Miller
2017-03-29 21:41 ` Eric Dumazet
2017-03-30 9:16 ` Vlad Zakharov
2017-03-30 13:25 ` Eric Dumazet [this message]
2017-04-26 12:56 ` Vlad Zakharov
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