linux-kernel - Re: [PATCH 1/1] um: ubd: Fix data corruption

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Message-ID: <4CAAE077.9010500@gmail.com>
Date:	Tue, 05 Oct 2010 10:23:19 +0200
From:	Tejun Heo <htejun@...il.com>
To:	Chris Frey <cdfrey@...rsquare.net>
CC:	Jens Axboe <jaxboe@...ionio.com>,
	Richard Weinberger <richard@....at>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jdike@...toit.com" <jdike@...toit.com>,
	"user-mode-linux-devel@...ts.sourceforge.net" 
	<user-mode-linux-devel@...ts.sourceforge.net>,
	"user-mode-linux-user@...ts.sourceforge.net" 
	<user-mode-linux-user@...ts.sourceforge.net>,
	"janjaap@....nl" <janjaap@....nl>,
	"geert@...ux-m68k.org" <geert@...ux-m68k.org>,
	"martin.petersen@...cle.com" <martin.petersen@...cle.com>,
	"adobriyan@...il.com" <adobriyan@...il.com>,
	"syzop@...nscan.org" <syzop@...nscan.org>
Subject: Re: [PATCH 1/1] um: ubd: Fix data corruption

On 10/04/2010 09:51 PM, Chris Frey wrote:
> On Mon, Oct 04, 2010 at 06:37:36PM +0200, Tejun Heo wrote:
>> Hello, sorry about chiming in later.  I was off last week.
> 
> No problem, I'm eager to test patches to fix this.
> 
>> I think we're on the right track.  The problem with Jens' patch was
>> that it didn't consider the fact that blk_end_request() now internally
>> updates the current position of the request, so if restart happens
>> after some of part of the request is complete it will end up adding
>> the offsets multiple times.  I think slightly modifying it to track
>> the current position instead of offset should do it.  Chris, can you
>> please try the following patch and see whether the problem goes away?
> 
> Unfortunately, this patch does not fix it for me.  I applied your patch
> to kernel 2.6.35.5, and got the usual error:
> 
> EXT3-fs error (device ubda): ext3_lookup: deleted inode referenced: 566188
> 
> Lots of them, actually.

Hmmmm, can you please give a shot at the following one?  Thank you.

diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 1bcd208..0435d21 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -163,6 +163,7 @@ struct ubd {
 	struct scatterlist sg[MAX_SG];
 	struct request *request;
 	int start_sg, end_sg;
+	sector_t rq_pos;
 };

 #define DEFAULT_COW { \
@@ -187,6 +188,7 @@ struct ubd {
 	.request =		NULL, \
 	.start_sg =		0, \
 	.end_sg =		0, \
+	.rq_pos =		0, \
 }

 /* Protected by ubd_lock */
@@ -1228,7 +1230,6 @@ static void do_ubd_request(struct request_queue *q)
 {
 	struct io_thread_req *io_req;
 	struct request *req;
-	sector_t sector;
 	int n;

 	while(1){
@@ -1239,12 +1240,12 @@ static void do_ubd_request(struct request_queue *q)
 				return;

 			dev->request = req;
+			dev->rq_pos = blk_rq_pos(req);
 			dev->start_sg = 0;
 			dev->end_sg = blk_rq_map_sg(q, req, dev->sg);
 		}

 		req = dev->request;
-		sector = blk_rq_pos(req);
 		while(dev->start_sg < dev->end_sg){
 			struct scatterlist *sg = &dev->sg[dev->start_sg];

@@ -1256,10 +1257,10 @@ static void do_ubd_request(struct request_queue *q)
 				return;
 			}
 			prepare_request(req, io_req,
-					(unsigned long long)sector << 9,
+					(unsigned long long)dev->rq_pos << 9,
 					sg->offset, sg->length, sg_page(sg));

-			sector += sg->length >> 9;
+			dev->rq_pos += sg->length >> 9;
 			n = os_write_file(thread_fd, &io_req,
 					  sizeof(struct io_thread_req *));
 			if(n != sizeof(struct io_thread_req *)){
--
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