linux/debian/patches-rt/0151-locking-rt-mutex-Flush-block-plug-on-__down_read.patch

From 0ff5fd365065d431385afd38184b9555c870ce3b Mon Sep 17 00:00:00 2001
From: Scott Wood <swood@redhat.com>
Date: Fri, 4 Jan 2019 15:33:21 -0500
Subject: [PATCH 151/325] locking/rt-mutex: Flush block plug on __down_read()
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.115-rt48.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(+)

diff --git a/kernel/locking/rwsem-rt.c b/kernel/locking/rwsem-rt.c
index 660e22caf709..f518495bd6cc 100644
--- 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(struct rw_semaphore *sem, int state)
 
 	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);
-- 
2.25.1