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