Jetpack/kernel_avc/kernel-4.9/rt-patches/0204-fs-jbd2-pull-your-plug...

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From fce77872d1d591b4c9896a8f82c728032b2bfb5c 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 204/352] 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.
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 4d5a5a4..b95c108 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -116,6 +116,8 @@ void __jbd2_log_wait_for_space(journal_t *journal)
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);
/*
--
2.7.4