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Date: Thu, 23 Nov 2017 15:42:31 +0100
From: Sebastian Siewior <bigeasy@linutronix.de>
To: Mike Galbraith <efault@gmx.de>
Cc: Mikulas Patocka <mpatocka@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>, Steven Rostedt <rostedt@goodmis.org>,
        linux-rt-users@vger.kernel.org
Subject: Re: [PATCH PREEMPT RT] rt-mutex: fix deadlock in device mapper
Message-ID: <20171123144231.GD2384@linutronix.de>
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On 2017-11-21 22:20:51 [+0100], Mike Galbraith wrote:
> On Tue, 2017-11-21 at 14:56 -0500, Mikulas Patocka wrote:
> > 
> > If we don't have any reason why it is needed to unplug block requests when 
> > a spinlock is taken - so let's not do this.
> 
> That's perfectly fine.  I guess I shouldn't have even mentioned having
> encountered unplug at mutex being insufficient.

While at it, I intend to drop
fs-jbd2-pull-your-plug-when-waiting-for-space.patch from the -RT queue
for v4.14 which does

--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -116,6 +116,8 @@ void __jbd2_log_wait_for_space(journal_t
 	nblocks = jbd2_space_needed(journal);
 	while (jbd2_log_space_left(journal) < nblocks) {
 		write_unlock(&journal->j_state_lock);
+		if (current->plug)
+			io_schedule();
 		mutex_lock(&journal->j_checkpoint_mutex);
 
 		/*

and is/was probably a workaround for the missing schedule while blocking
on mutex/rwsem.

> 	-Mike

Sebastian