Messages in this thread | | | Date | Mon, 18 May 2015 16:18:29 -0700 | From | santosh shilimkar <> | Subject | Re: [Regression] Guest fs corruption with 'block: loop: improve performance via blk-mq' |
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On 5/18/2015 4:14 PM, Ming Lei wrote: > 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 > Our emails crossed. I did port that one patch alone and confirm that the issue is getting fixed. That patch also should go to v4.0 stable then along with above 2.
Regards, Santosh
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