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@xxxxxxxxxx> 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. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
