linux-kernel - [63/73] block: blk-flush shouldnt call directly into q->request_fn() __blk_run

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Message-Id: <20110305005640.736605611@clark.kroah.org>
Date:	Fri, 04 Mar 2011 16:56:08 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Tejun Heo <tj@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Jens Axboe <jaxboe@...ionio.com>
Subject: [63/73] block: blk-flush shouldnt call directly into q->request_fn() __blk_run_queue()

2.6.37-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Tejun Heo <tj@...nel.org>

commit 255bb490c8c27eed484d538efe6ef6a7473bd3f6 upstream.

blk-flush decomposes a flush into sequence of multiple requests.  On
completion of a request, the next one is queued; however, block layer
must not implicitly call into q->request_fn() directly from completion
path.  This makes the queue behave unexpectedly when seen from the
drivers and violates the assumption that q->request_fn() is called
with process context + queue_lock.

This patch makes blk-flush the following two changes to make sure
q->request_fn() is not called directly from request completion path.

- blk_flush_complete_seq_end_io() now asks __blk_run_queue() to always
  use kblockd instead of calling directly into q->request_fn().

- queue_next_fseq() uses ELEVATOR_INSERT_REQUEUE instead of
  ELEVATOR_INSERT_FRONT so that elv_insert() doesn't try to unplug the
  request queue directly.

Reported by Jan in the following threads.

 http://thread.gmane.org/gmane.linux.ide/48778
 http://thread.gmane.org/gmane.linux.ide/48786

stable: applicable to v2.6.37.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Jan Beulich <JBeulich@...ell.com>
Cc: "David S. Miller" <davem@...emloft.net>
Signed-off-by: Jens Axboe <jaxboe@...ionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 block/blk-flush.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -66,10 +66,12 @@ static void blk_flush_complete_seq_end_i
 
 	/*
 	 * Moving a request silently to empty queue_head may stall the
-	 * queue.  Kick the queue in those cases.
+	 * queue.  Kick the queue in those cases.  This function is called
+	 * from request completion path and calling directly into
+	 * request_fn may confuse the driver.  Always use kblockd.
 	 */
 	if (was_empty && next_rq)
-		__blk_run_queue(q, false);
+		__blk_run_queue(q, true);
 }
 
 static void pre_flush_end_io(struct request *rq, int error)
@@ -130,7 +132,7 @@ static struct request *queue_next_fseq(s
 		BUG();
 	}
 
-	elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
+	elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
 	return rq;
 }
 


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