linux-kernel - [PATCH 3.12 076/206] um: ubd: Fix for processes stuck in D state forever

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Message-Id: <63550e4be59837925cc1bee167bee83a90ce974c.1416319692.git.jslaby@suse.cz>
Date:	Tue, 18 Nov 2014 15:07:11 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Thorsten Knabe <linux@...rsten-knabe.de>,
	Richard Weinberger <richard@....at>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 076/206] um: ubd: Fix for processes stuck in D state forever

From: Thorsten Knabe <linux@...rsten-knabe.de>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 2a2361228c5e6d8c1733f00653481de918598e50 upstream.

Starting with Linux 3.12 processes get stuck in D state forever in
UserModeLinux under sync heavy workloads. This bug was introduced by
commit 805f11a0d5 (um: ubd: Add REQ_FLUSH suppport).
Fix bug by adding a check if FLUSH request was successfully submitted to
the I/O thread and keeping the FLUSH request on the request queue on
submission failures.

Fixes: 805f11a0d5 (um: ubd: Add REQ_FLUSH suppport)
Signed-off-by: Thorsten Knabe <linux@...rsten-knabe.de>
Signed-off-by: Richard Weinberger <richard@....at>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/um/drivers/ubd_kern.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 3716e6952554..e8ab93c3e638 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -1277,7 +1277,7 @@ static void do_ubd_request(struct request_queue *q)
 
 	while(1){
 		struct ubd *dev = q->queuedata;
-		if(dev->end_sg == 0){
+		if(dev->request == NULL){
 			struct request *req = blk_fetch_request(q);
 			if(req == NULL)
 				return;
@@ -1299,7 +1299,8 @@ static void do_ubd_request(struct request_queue *q)
 				return;
 			}
 			prepare_flush_request(req, io_req);
-			submit_request(io_req, dev);
+			if (submit_request(io_req, dev) == false)
+				return;
 		}
 
 		while(dev->start_sg < dev->end_sg){
-- 
2.1.3

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