linux-kernel - Re: [PATCH RT] rtmutex: Flush block plug on __down

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Message-ID: <20190109094849.m7idtma5hoew3eyp@linutronix.de>
Date:   Wed, 9 Jan 2019 10:48:49 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Scott Wood <swood@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Mikulas Patocka <mpatocka@...hat.com>,
        linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RT] rtmutex: Flush block plug on __down_read()

On 2019-01-04 15:33:21 [-0500], Scott Wood wrote:
> +	/*
> +	 * If sem->rtmutex blocks, the function sched_submit_work will not
> +	 * call blk_schedule_flush_plug (because tsk_is_pi_blocked would be
> +	 * true).  We must call blk_schedule_flush_plug here; if we don't
> +	 * call it, an I/O deadlock may occur.
> +	 */

I kept the original comment plus I replaced device-mapper with I/O (the
patch said already that it is not device-mapper specific and may occur
with ext4 as well).

Sebastian