netdev - Re: [PATCH v3 net] net: solve a NAPI race

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Message-ID: <20170228081702.35ba7a6a@xeon-e3>
Date:   Tue, 28 Feb 2017 08:17:02 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 net] net: solve a NAPI race

On Mon, 27 Feb 2017 12:18:31 -0800
Eric Dumazet <eric.dumazet@...il.com> wrote:

> This can happen with busy polling users, or if gro_flush_timeout is
> used. But some other uses of napi_schedule() in drivers can cause this
> as well.

Where were IRQ's re-enabled?


> thread 1                                 thread 2 (could be on same cpu)
> 
> // busy polling or napi_watchdog()
> napi_schedule();
> ...
> napi->poll()
> 
> device polling:
> read 2 packets from ring buffer
>                                           Additional 3rd packet is available.
>                                           device hard irq
> 
>                                           // does nothing because NAPI_STATE_SCHED bit is owned by thread 1
>                                           napi_schedule();
>                                           
> napi_complete_done(napi, 2);
> rearm_irq();

Maybe just as simple as using irqsave/irqrestore in driver.