linux-kernel - Re: [PATCH RT] net: Have __napi_schedule

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Message-ID: <20161207091040.qnx3znzpffobli7c@linutronix.de>
Date:   Wed, 7 Dec 2016 10:10:40 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Clark Williams <williams@...hat.com>,
        "Luis Claudio R. Goncalves" <lclaudio@...g.org>,
        John Kacur <jkacur@...hat.com>
Subject: Re: [PATCH RT] net: Have __napi_schedule_irqoff() disable interrupts
 on RT

On 2016-12-06 17:50:30 [-0500], Steven Rostedt wrote:
> A customer hit a crash where the napi sd->poll_list became corrupted.
> The customer had the bnx2x driver, which does a
> __napi_schedule_irqoff() in its interrupt handler. Unfortunately, when
> running with CONFIG_PREEMPT_RT_FULL, this interrupt handler is run as a
> thread and is preemptable. The call to ____napi_schedule() must be done
> with interrupts disabled to protect the per cpu softnet_data's
> poll_list, which is protected by disabling interrupts (disabling
> preemption is enough when all interrupts are threaded and
> local_bh_disable() can't preempt).
> 
> As bnx2x isn't the only driver that does this, the safest thing to do
> is to make __napi_schedule_irqoff() call __napi_schedule() instead when
> CONFIG_PREEMPT_RT_FULL is enabled, which will call local_irq_save()
> before calling ____napi_schedule().

It would work RT wise. But don't have the same problem if you boot the
kernel with threadirqs ?

Sebastian