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From: Scott Wood <swood@redhat.com>
Date: Fri, 4 Jan 2019 15:33:21 -0500
Subject: [PATCH] locking/rt-mutex: Flush block plug on __down_read()
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.0/older/patches-5.0.7-rt5.tar.xz
__down_read() bypasses the rtmutex frontend to call
rt_mutex_slowlock_locked() directly, and thus it needs to call
blk_schedule_flush_flug() itself.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Scott Wood <swood@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/locking/rwsem-rt.c | 9 +++++++++
1 file changed, 9 insertions(+)
--- a/kernel/locking/rwsem-rt.c
+++ b/kernel/locking/rwsem-rt.c
@@ -1,5 +1,6 @@
/*
*/
+#include <linux/blkdev.h>
#include <linux/rwsem.h>
#include <linux/sched/debug.h>
#include <linux/sched/signal.h>
@@ -87,6 +88,14 @@ static int __sched __down_read_common(st
if (__down_read_trylock(sem))
return 0;
+ /*
+ * If rt_mutex blocks, the function sched_submit_work will not call
+ * blk_schedule_flush_plug (because tsk_is_pi_blocked would be true).
+ * We must call blk_schedule_flush_plug here, if we don't call it,
+ * a deadlock in I/O may happen.
+ */
+ if (unlikely(blk_needs_flush_plug(current)))
+ blk_schedule_flush_plug(current);
might_sleep();
raw_spin_lock_irq(&m->wait_lock);
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