netdev - Re: [PATCH net] net/mlx4_en: reception NAPI/IRQ race breaker

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Message-ID: <1488130836.9415.155.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Sun, 26 Feb 2017 09:40:36 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Saeed Mahameed <saeedm@....mellanox.co.il>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: [PATCH net] net/mlx4_en: reception NAPI/IRQ race breaker

On Sun, 2017-02-26 at 09:34 -0800, Eric Dumazet wrote:

> I do not believe this bug is mlx4 specific.
> 
> Anything doing the following while hard irq were not masked :
> 
> local_bh_disable();
> napi_reschedule(&priv->rx_cq[ring]->napi);
> local_bh_enable();
> 
> Like in mlx4_en_recover_from_oom()
> 
> Can trigger the issue really.
> 
> Unfortunately I do not see how core layer can handle this.
> Only the driver hard irq could possibly know that it could not grab
> NAPI_STATE_SCHED

Actually we could use an additional bit for that, that the driver would
set even if NAPI_STATE_SCHED could not be grabbed.

Let me try something.