From: Stephen Hemminger <stephen@networkplumber.org>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: David Miller <davem@davemloft.net>, netdev <netdev@vger.kernel.org>
Subject: Re: [PATCH v3 net] net: solve a NAPI race
Date: Mon, 27 Feb 2017 14:14:03 -0800 [thread overview]
Message-ID: <20170227141403.714490f7@xeon-e3> (raw)
In-Reply-To: <1488226711.9415.204.camel@edumazet-glaptop3.roam.corp.google.com>
On Mon, 27 Feb 2017 12:18:31 -0800
Eric Dumazet <eric.dumazet@gmail.com> wrote:
> 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();
The original design (as Davem mentioned) was that IRQ's must be disabled
during device polling. If that was true, then the race above
would be impossible. Also NAPI assumes interrupts are level triggered.
next prev parent reply other threads:[~2017-02-27 22:14 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-25 14:22 [PATCH net] net/mlx4_en: reception NAPI/IRQ race breaker Eric Dumazet
2017-02-26 16:32 ` Saeed Mahameed
2017-02-26 17:34 ` Eric Dumazet
2017-02-26 17:40 ` Eric Dumazet
2017-02-26 18:03 ` Eric Dumazet
2017-02-27 3:31 ` [PATCH net] net: solve a NAPI race Eric Dumazet
2017-02-27 14:06 ` Eric Dumazet
2017-02-27 14:21 ` [PATCH v2 " Eric Dumazet
2017-02-27 16:19 ` David Miller
2017-02-27 16:44 ` Eric Dumazet
2017-02-27 17:10 ` Eric Dumazet
2017-02-28 2:08 ` David Miller
2017-03-01 0:22 ` Francois Romieu
2017-03-01 1:04 ` Stephen Hemminger
2017-02-27 21:00 ` Alexander Duyck
2017-02-27 20:18 ` [PATCH v3 " Eric Dumazet
2017-02-27 22:14 ` Stephen Hemminger [this message]
2017-02-27 22:35 ` Eric Dumazet
2017-02-27 22:44 ` Stephen Hemminger
2017-02-27 22:48 ` David Miller
2017-02-27 23:23 ` Stephen Hemminger
2017-02-28 10:14 ` David Laight
2017-02-28 13:04 ` Eric Dumazet
2017-02-28 13:20 ` Eric Dumazet
2017-02-28 16:17 ` Stephen Hemminger
2017-02-28 16:57 ` Eric Dumazet
2017-02-28 18:34 ` [PATCH v4 " Eric Dumazet
2017-03-01 17:53 ` David Miller
2017-02-28 17:20 ` [PATCH v2 " Alexander Duyck
2017-02-28 17:47 ` Eric Dumazet
2017-03-01 10:41 ` David Laight
2017-03-01 16:14 ` Alexander Duyck
2017-03-01 17:32 ` Eric Dumazet
2017-03-02 10:24 ` David Laight
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