Re: problems I encountered using xen-4.1-testing and xen-unstable

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Jan 05, 2012 at 08:01:22AM +0000, Jan Beulich wrote:
> >>> On 05.01.12 at 00:35, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> > On Wed, Jan 04, 2012 at 10:07:29PM +0000, Kay, Allen M wrote:
> >> 2)      Xen-unstable:  I get ext4 file system corruption when booting xen 
> > with the latest upstream Linux kernel.
> > 
> > 
> > That I hadn't seen. Is this with dom0 or domU? There is one bug in the 
> > 2.6.18 kernel in blkback if you are using that version.
> 
> Which one are you referring to?

The fix you posted some time ago. Not all distros have picked it up.

# HG changeset patch
From: Jan Beulich <jbeulich@novell.com>
# Date 1306409621 -3600
# Node ID 876a5aaac0264cf38cae6581e5714b93ec380aaa
# Parent  aedb712c05cf065e943e15d0f38597c2e80f7982
Subject: xen/blkback: don't fail empty barrier requests

The sector number on empty barrier requests may (will?) be
uninitialized (neither bio_init() nor rq_init() set the respective
fields), which allows for exceeding the actual (virtual) disk's size.

Inspired by Konrad's "When writting barriers set the sector number to
zero...", but instead of zapping the sector number (which is wrong for
non-empty ones) just ignore the sector number when the sector count is
zero.

While at it also add overflow checking to the math in vbd_translate().

Signed-off-by: Jan Beulich <jbeulich@novell.com>

diff -r aedb712c05cf -r 876a5aaac026 drivers/xen/blkback/vbd.c
--- a/drivers/xen/blkback/vbd.c	Thu May 26 08:09:04 2011 +0100
+++ b/drivers/xen/blkback/vbd.c	Thu May 26 12:33:41 2011 +0100
@@ -108,8 +108,14 @@ int vbd_translate(struct phys_req *req, 
 	if ((operation != READ) && vbd->readonly)
 		goto out;
 
-	if (unlikely((req->sector_number + req->nr_sects) > vbd_sz(vbd)))
-		goto out;
+	if (likely(req->nr_sects)) {
+		blkif_sector_t end = req->sector_number + req->nr_sects;
+
+		if (unlikely(end < req->sector_number))
+			goto out;
+		if (unlikely(end > vbd_sz(vbd)))
+			goto out;
+	}
 
 	req->dev  = vbd->pdevice;
 	req->bdev = vbd->bdev;

> 
> Jan