From: Daniel Wagner <dwagner@suse.de>
To: John Ogness <john.ogness@linutronix.de>
Cc: Jens Axboe <axboe@kernel.dk>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Thomas Gleixner <tglx@linutronix.de>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] block: remove retry loop in ioc_release_fn()
Date: Tue, 23 Jun 2020 16:30:26 +0200 [thread overview]
Message-ID: <20200623143026.ei3z4wryjbqjdf2x@beryllium.lan> (raw)
In-Reply-To: <20200619151718.22338-3-john.ogness@linutronix.de>
On Fri, Jun 19, 2020 at 05:23:18PM +0206, John Ogness wrote:
> The reverse-order double lock dance in ioc_release_fn() is using a
> retry loop. This is a problem on PREEMPT_RT because it could preempt
> the task that would release q->queue_lock and thus live lock in the
> retry loop.
>
> RCU is already managing the freeing of the request queue and icq. If
> the trylock fails, use RCU to guarantee that the request queue and
> icq are not freed and re-acquire the locks in the correct order,
> allowing forward progress.
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
Again, after starring on it for while and reading up and down,
I'd say, it looks good. Also a quick test run with blktests and
lockdep enabled didn't produce any warnings.
Reviewed-by: Daniel Wagner <dwagner@suse.de>
next prev parent reply other threads:[~2020-06-23 14:30 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-19 15:17 [PATCH 0/2] block: remove retry loop John Ogness
2020-06-19 15:17 ` [PATCH 1/2] block: remove unnecessary ioc nested locking John Ogness
2020-06-23 11:50 ` Daniel Wagner
2020-06-19 15:17 ` [PATCH 2/2] block: remove retry loop in ioc_release_fn() John Ogness
2020-06-23 14:30 ` Daniel Wagner [this message]
2020-07-16 16:23 ` [PATCH 0/2] block: remove retry loop Jens Axboe
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