From 3c96520e15425f4ce3ad7931d34c2172753dd4b9 Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Mon, 17 Feb 2014 17:30:03 +0100
Subject: [PATCH 213/414] fs: jbd2: pull your plug when waiting for space

Two cps in parallel managed to stall the the ext4 fs. It seems that
journal code is either waiting for locks or sleeping waiting for
something to happen. This seems similar to what Mike observed on ext3,
here is his description:

|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.

Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 fs/jbd2/checkpoint.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index d4c7e470dec8..f0c3d193392c 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -125,6 +125,8 @@ void __jbd2_log_wait_for_space(journal_t *journal)
 		if (journal->j_flags & JBD2_ABORT)
 			return;
 		write_unlock(&journal->j_state_lock);
+		if (current->plug)
+			io_schedule();
 		mutex_lock(&journal->j_checkpoint_mutex);
 
 		/*
-- 
2.10.2

