linux-kernel - Re: Deadlocks due to per-process plugging

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Date:	Mon, 16 Jul 2012 12:08:23 +0200
From:	Mike Galbraith <efault@....de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Jan Kara <jack@...e.cz>, Jeff Moyer <jmoyer@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Jens Axboe <jaxboe@...ionio.com>, mgalbraith@...e.com
Subject: Re: Deadlocks due to per-process plugging

Hm, wonder how bad this sucks.. and if I should go hide under a big
sturdy rock after I poke xmit :)

---
 block/blk-core.c |    1 +
 kernel/rtmutex.c |   11 +++++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2782,6 +2782,7 @@ void blk_flush_plug_list(struct blk_plug
 	if (q)
 		queue_unplugged(q, depth, from_schedule);
 }
+EXPORT_SYMBOL(blk_flush_plug_list);
 
 void blk_finish_plug(struct blk_plug *plug)
 {
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -20,6 +20,7 @@
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/timer.h>
+#include <linux/blkdev.h>
 
 #include "rtmutex_common.h"
 
@@ -647,8 +648,11 @@ static inline void rt_spin_lock_fastlock
 
 	if (likely(rt_mutex_cmpxchg(lock, NULL, current)))
 		rt_mutex_deadlock_account_lock(lock, current);
-	else
+	else {
+		if (blk_needs_flush_plug(current))
+			blk_schedule_flush_plug(current);
 		slowfn(lock);
+	}
 }
 
 static inline void rt_spin_lock_fastunlock(struct rt_mutex *lock,
@@ -1104,8 +1108,11 @@ rt_mutex_fastlock(struct rt_mutex *lock,
 	if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 		rt_mutex_deadlock_account_lock(lock, current);
 		return 0;
-	} else
+	} else {
+		if (blk_needs_flush_plug(current))
+			blk_schedule_flush_plug(current);
 		return slowfn(lock, state, NULL, detect_deadlock);
+	}
 }
 
 static inline int


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