linux-kernel - Re: [PATCH PREEMPT RT] rt-mutex: fix deadlock in device mapper

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Message-ID: <1511234430.7672.26.camel@gmx.de>
Date:   Tue, 21 Nov 2017 04:20:30 +0100
From:   Mike Galbraith <efault@....de>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Sebastian Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-rt-users@...r.kernel.org
Subject: Re: [PATCH PREEMPT RT] rt-mutex: fix deadlock in device mapper

On Mon, 2017-11-20 at 16:33 -0500, Mikulas Patocka wrote:
> 
> Is there some specific scenario where you need to call 
> blk_schedule_flush_plug from rt_spin_lock_fastlock?

Excellent question.  What's the difference between not getting IO
started because you meet a mutex with an rt_mutex under the hood, and
not getting IO started because you meet a spinlock with an rt_mutex
under the hood?  If just doing the mutex side puts this thing back to
sleep, I'm happy.

	-Mike