netdev - Re: [PATCH net-next] net/mlx5: Make ASO poll CQ usable in atomic context

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Message-ID: <20220924172425.bfagbky4h5tbcxf4@fedora>
Date:   Sat, 24 Sep 2022 10:24:25 -0700
From:   Saeed Mahameed <saeedm@...dia.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Leon Romanovsky <leonro@...dia.com>,
        Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next] net/mlx5: Make ASO poll CQ usable in atomic
 context

On 24 Sep 14:17, Leon Romanovsky wrote:
>From: Leon Romanovsky <leonro@...dia.com>
>
>Poll CQ functions shouldn't sleep as they are called in atomic context.
>The following splat appears once the mlx5_aso_poll_cq() is used in such
>flow.
>
> BUG: scheduling while atomic: swapper/17/0/0x00000100

...

> 	/* With newer FW, the wait for the first ASO WQE is more than 2us, put the wait 10ms. */
>-	err = mlx5_aso_poll_cq(aso, true, 10);
>+	expires = jiffies + msecs_to_jiffies(10);
>+	do {
>+		err = mlx5_aso_poll_cq(aso, true);
>+	} while (err && time_is_after_jiffies(expires));
> 	mutex_unlock(&flow_meters->aso_lock);
         ^^^^
busy poll won't work, this mutex is held and can sleep anyway.
Let's discuss internally and solve this by design.