Messages in this thread | | | Date | Tue, 19 May 2015 07:14:22 +0800 | Subject | Re: [Regression] Guest fs corruption with 'block: loop: improve performance via blk-mq' | From | Ming Lei <> |
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On Tue, May 19, 2015 at 2:07 AM, santosh shilimkar <santosh.shilimkar@oracle.com> wrote: > On 5/17/2015 6:26 PM, Ming Lei wrote: >> >> Hi Santosh, >> >> Thanks for your report! >> >> On Sun, May 17, 2015 at 4:13 AM, santosh shilimkar >> <santosh.shilimkar@oracle.com> wrote: >>> >>> Hi Ming Lei, Jens, >>> >>> While doing few tests with recent kernels with Xen Server, >>> we saw guests(DOMU) disk image getting corrupted while booting it. >>> Strangely the issue is seen so far only with disk image over ocfs2 >>> volume. If the same image kept on the EXT3/4 drive, no corruption >>> is observed. The issue is easily reproducible. You see the flurry >>> of errors while guest is mounting the file systems. >>> >>> After doing some debug and bisects, we zeroed down the issue with >>> commit "b5dd2f6 block: loop: improve performance via blk-mq". With >>> that commit reverted the corruption goes away. >>> >>> Some more details on the test setup: >>> 1. OVM(XEN) Server kernel(DOM0) upgraded to more recent kernel >>> which includes commit b5dd2f6. Boot the Server. >>> 2. On DOM0 file system create a ocfs2 volume >>> 3. Keep the Guest(VM) disk image on ocfs2 volume. >>> 4. Boot guest image. (xm create vm.cfg) >> >> >> I am not familiar with xen, so is the image accessed via >> loop block inside of guest VM? Is he loop block created >> in DOM0 or guest VM? >> > Guest. The Guest disk image is represented as a file by loop > device. > >>> 5. Observe the VM boot console log. VM itself use the EXT3 fs. >>> You will see errors like below and after this boot, that file >>> system/disk-image gets corrupted and mostly won't boot next time. >> >> >> OK, that means the image is corrupted by VM booting. >> > Right > > [...] > >>> >>> From the debug of the actual data on the disk vs what is read by >>> the guest VM, we suspect the *reads* are actually not going all >>> the way to disk and possibly returning the wrong data. Because >>> the actual data on ocfs2 volume at those locations seems >>> to be non-zero where as the guest seems to be read it as zero. >> >> >> Two big changes in the patchset are: 1) use blk-mq request based IO; >> 2) submit I/O concurrently(write vs. write is still serialized) >> >> Could you apply the patch in below link to see if it can fix the issue? >> BTW, this patch only removes concurrent submission. >> >> http://marc.info/?t=143093223200004&r=1&w=2 >> > What kernel is this patch generated against ? It doesn't apply against > v4.0. Does this need the AIO/DIO conversion patches as well. Do you > have the dependent patch-set I can't apply it against v4.0.
My fault, the patch is against -next tree, but you just need another two patches for applying this one:
http://git.kernel.org/cgit/linux/kernel/git/axboe/linux-block.git/commit/?h=for-next&id=f4aa4c7bbac6c4afdd4adccf90898c1a3685396d
http://git.kernel.org/cgit/linux/kernel/git/axboe/linux-block.git/commit/?h=for-next&id=4d4e41aef9429872ea3b105e83426941f7185ab6
Thanks, Ming
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