> On Aug 17, 2023, at 11:57 AM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote: > > > >> On Aug 17, 2023, at 11:52 AM, Maxim Levitsky <mlevitsk@xxxxxxxxxx> wrote: >> >> Hi! >> >> I just updated my developement systems to 6.5-rc6 (from 6.4) and now I can't start a VM >> with a disk which is mounted over the NFS. >> >> The VM has two qcow2 files, one depends on another and qemu opens both. >> >> This is the command line of qemu: >> >> -drive if=none,id=os_image,file=./disk_s1.qcow2,aio=native,discard=unmap,cache=none >> >> The disk_s1.qcow2 depends on disk_s0.qcow2 >> >> However this is what I get: >> >> qemu-system-x86_64: -drive if=none,id=os_image,file=./disk_s1.qcow2,aio=native,discard=unmap,cache=none: Could not open backing file: Could not open './QFI?': No such file or directory >> >> 'QFI?' is qcow2 file signature, which signals that there might be some nasty corruption happening. >> >> The program was supposed to read a field inside the disk_s1.qcow2 file which should read 'disk_s0.qcow2' >> but instead it seems to read the first 4 bytes of the file. >> >> >> Bisect leads to the above commit. Reverting it was not possible due to many changes. >> >> Both the client and the server were tested with the 6.5-rc6 kernel, but once rebooting the server into >> the 6.4, the bug disappeared, thus I did a bisect on the server. >> >> When I tested a version before the offending commit on the server, the 6.5-rc6 client was able to work with it, >> which increases the chances that the bug is in nfsd. >> >> Switching qemu to use write back paging also helps (aio=threads,discard=unmap,cache=writeback) >> The client and the server (both 6.5-rc6) work with this configuration. >> >> Running the VM on the same machine (also 6.5-rc6) where the VM disk is located (thus avoiding NFS) works as well. >> >> I tested several VMs that I have, all are affected in the same way. >> >> I run somewhat outdated qemu, but running the latest qemu doesn't make a difference. >> >> I use nfs4. >> >> I can test patches and provide more info if needed. > > Linus just merged a possible fix for this issue. See: > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/ master In particular: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c96e2a695e00bca5487824d84b85aab6aa2c1891 -- Chuck Lever
