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

From: Tejun Heo
Date: Tue Oct 05 2010 - 04:21:29 EST


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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