[3.13.y.z extended stable] Patch "um: ubd: Fix for processes stuck in D state forever" has been added to staging queue

Kamal Mostafa kamal at canonical.com
Tue Oct 21 20:09:32 UTC 2014

This is a note to let you know that I have just added a patch titled

    um: ubd: Fix for processes stuck in D state forever

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:


This patch is scheduled to be released in version

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see



>From 103ed905d11a647dafaa626380bcd7d9a0f8ce57 Mon Sep 17 00:00:00 2001
From: Thorsten Knabe <linux at thorsten-knabe.de>
Date: Sat, 23 Aug 2014 15:47:38 +0200
Subject: um: ubd: Fix for processes stuck in D state forever

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 at thorsten-knabe.de>
Signed-off-by: Richard Weinberger <richard at nod.at>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 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 3716e69..e8ab93c 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)

 		struct ubd *dev = q->queuedata;
-		if(dev->end_sg == 0){
+		if(dev->request == NULL){
 			struct request *req = blk_fetch_request(q);
 			if(req == NULL)
@@ -1299,7 +1299,8 @@ static void do_ubd_request(struct request_queue *q)
 			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){

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