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Date: Mon, 18 May 2015 11:07:50 -0700 From: santosh shilimkar <santosh.shilimkar@...cle.com> To: Ming Lei <ming.lei@...onical.com> CC: Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [Regression] Guest fs corruption with 'block: loop: improve performance via blk-mq' 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@...cle.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. Regards, Santosh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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