netdev - Re: [PATCH net-next v2] net: sched: Avoid using yield() in a busy waiting loop

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Message-Id: <20191017.153340.1998610553660604312.davem@davemloft.net>
Date:   Thu, 17 Oct 2019 15:33:40 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     bigeasy@...utronix.de
Cc:     sergei.shtylyov@...entembedded.com, netdev@...r.kernel.org,
        jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        edumazet@...gle.com, tglx@...utronix.de, mkl@...gutronix.de,
        peterz@...radead.org
Subject: Re: [PATCH net-next v2] net: sched: Avoid using yield() in a busy
 waiting loop

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Date: Wed, 16 Oct 2019 10:28:33 +0200

> From: Marc Kleine-Budde <mkl@...gutronix.de>
> 
> With threaded interrupts enabled, the interrupt thread runs as SCHED_RR
> with priority 50. If a user application with a higher priority preempts
> the interrupt thread and tries to shutdown the network interface then it
> will loop forever. The kernel will spin in the loop waiting for the
> device to become idle and the scheduler will never consider the
> interrupt thread because its priority is lower.
> 
> Avoid the problem by sleeping for a jiffy giving other tasks,
> including the interrupt thread, a chance to run and make progress.
> 
> In the original thread it has been suggested to use wait_event() and
> properly waiting for the state to occur. DaveM explained that this would
> require to add expensive checks in the fast paths of packet processing.
> 
> Link: https://lkml.kernel.org/r/1393976987-23555-1-git-send-email-mkl@pengutronix.de
> Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
> [bigeasy: Rewrite commit message, add comment, use
>           schedule_timeout_uninterruptible()]
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
> v1…v2: Typo fixes, noticed by Sergei Shtylyov.

Applied, thank you.