From 535b939b3edff8f5bdf83c3b0bfc065ed9af17e4 Mon Sep 17 00:00:00 2001
From: Mike Galbraith <mgalbraith@suse.de>
Date: Wed, 11 Jul 2012 22:05:20 +0000
Subject: fs, jbd: pull your plug when waiting for space

With an -rt kernel, and a heavy sync IO load, tasks can jam
up on journal locks without unplugging, which can lead to
terminal IO starvation.  Unplug and schedule when waiting for space.

Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Theodore Tso <tytso@mit.edu>
Link: http://lkml.kernel.org/r/1341812414.7370.73.camel@marge.simpson.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/fs/jbd/checkpoint.c b/fs/jbd/checkpoint.c
index 08c0304..95debd7 100644
--- a/fs/jbd/checkpoint.c
+++ b/fs/jbd/checkpoint.c
@@ -129,6 +129,8 @@ void __log_wait_for_space(journal_t *journal)
 		if (journal->j_flags & JFS_ABORT)
 			return;
 		spin_unlock(&journal->j_state_lock);
+		if (current->plug)
+			io_schedule();
 		mutex_lock(&journal->j_checkpoint_mutex);
 
 		/*
-- 
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