lkml.org 
[lkml]   [2010]   [Jun]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Wrong DIF guard tag on ext2 write
On Tue, Jun 01, 2010 at 09:58:18AM -0400, Chris Mason wrote:
> On Tue, Jun 01, 2010 at 03:50:59PM +0200, Christof Schmitt wrote:
> > On Tue, Jun 01, 2010 at 09:03:25AM -0400, Chris Mason wrote:
> > > On Tue, Jun 01, 2010 at 12:30:42PM +0200, Christof Schmitt wrote:
> > > > On Mon, May 31, 2010 at 06:30:05PM +0300, Boaz Harrosh wrote:
> > > > > On 05/31/2010 06:01 PM, James Bottomley wrote:
> > > > > > On Mon, 2010-05-31 at 10:20 -0400, Martin K. Petersen wrote:
> > > > > >>>>>>> "Christof" == Christof Schmitt <christof.schmitt@de.ibm.com> writes:
> > > > > >>
> > > > > >> Christof> Since the guard tags are created in Linux, it seems that the
> > > > > >> Christof> data attached to the write request changes between the
> > > > > >> Christof> generation in bio_integrity_generate and the call to
> > > > > >> Christof> sd_prep_fn.
> > > > > >>
> > > > > >> Yep, known bug. Page writeback locking is messed up for buffer_head
> > > > > >> users. The extNfs folks volunteered to look into this a while back but
> > > > > >> I don't think they have found the time yet.
> > > > > >>
> > > > > >>
> > > > > >> Christof> Using ext3 or ext4 instead of ext2 does not show the problem.
> > > > > >>
> > > > > >> Last I looked there were still code paths in ext3 and ext4 that
> > > > > >> permitted pages to be changed during flight. I guess you've just been
> > > > > >> lucky.
> > > > > >
> > > > > > Pages have always been modifiable in flight. The OS guarantees they'll
> > > > > > be rewritten, so the drivers can drop them if it detects the problem.
> > > > > > This is identical to the iscsi checksum issue (iscsi adds a checksum
> > > > > > because it doesn't trust TCP/IP and if the checksum is generated in
> > > > > > software, there's time between generation and page transmission for the
> > > > > > alteration to occur). The solution in the iscsi case was not to
> > > > > > complain if the page is still marked dirty.
> > > > > >
> > > > >
> > > > > And also why RAID1 and RAID4/5/6 need the data bounced. I wish VFS
> > > > > would prevent data writing given a device queue flag that requests
> > > > > it. So all these devices and modes could just flag the VFS/filesystems
> > > > > that: "please don't allow concurrent writes, otherwise I need to copy data"
> > > > >
> > > > > From what Chris Mason has said before, all the mechanics are there, and it's
> > > > > what btrfs is doing. Though I don't know how myself?
> > > >
> > > > I also tested with btrfs and invalid guard tags in writes have been
> > > > encountered as well (again in 2.6.34). The only difference is that no
> > > > error was reported to userspace, although this might be a
> > > > configuration issue.
> > >
> > > This would be a btrfs bug. We have strict checks in place that are
> > > supposed to prevent buffers changing while in flight. What was the
> > > workload that triggered this problem?
> >
> > I am running an internal test tool that creates files with a known
> > pattern until the disk is full, reads the data to verify if the
> > pattern is still intact, removes the files and starts over.
>
> Ok, is the lba in the output the sector offset? We can map that to a
> btrfs block and figure out what it was.
>
> Btrfs never complains about the IO error? We really should explode.

Right now, i don't have a system available to continue with this. When
i have a change to run it again, i can try the latest rc kernel to see
if there is any difference.


\
 
 \ /
  Last update: 2010-06-08 09:21    [W:0.090 / U:3.764 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site