canonical-ubuntu-qa team mailing list archive

[asmadeus <2056461@xxxxxxxxxxxxxxxxxx>]

That won't be enough imo, there are two problems:
- We're truncating the read request to the cached i_size
- that odd O_NONBLOCK behaviour on regular files 9p used to have

In this particular reproducer O_NONBLOCK happened to be set (in eofcat)
so that part of the discussion came up, but the problem here really is
the truncated IO -- in cache=none, we shouldn't rely on prior knowledge
at all, so if the IO asked for a 1000 bytes read we should try to read
1000 bytes even if we previously had i_size=10 in the inode

Since nothing else refreshes i_size here, just bailing out because of
the O_NONBLOCK won't make the request proceed further

@Christian at this point I feel that we have a clear enough
understanding of the problem that it'll be faster to fix than to revert;
I'm sorry about the whole thing that should have been much smoother but
we're almost there, please hang on a little bit more.

-- 
You received this bug notification because you are a member of
Canonical's Ubuntu QA, which is subscribed to autopkgtest in Ubuntu.
https://bugs.launchpad.net/bugs/2056461

Title:
  autopkgtest-virt-qemu on noble images sometimes hangs doing copydown

Status in Linux:
  Confirmed
Status in autopkgtest package in Ubuntu:
  Confirmed
Status in linux package in Ubuntu:
  In Progress
Status in autopkgtest package in Debian:
  New

Bug description:
  [Impact]

  It seems that kernel 6.8 introduced a regression in the 9pfs related
  to caching and netfslib, that can cause some user-space apps to read
  content from files that is not up-to-date (when they are used in a
  producer/consumer fashion).

  It seems that the offending commit is this one:

   80105ed2fd27 ("9p: Use netfslib read/write_iter")

  Reverting the commit seems to fix the problem. However the actual bug
  might be in netfslib or how netfslib is used in the 9p context.

  The regression has been reported upstream and we are still
  investigating (https://lore.kernel.org/lkml/Zj0ErxVBE3DYT2Ea@gpd/).

  In the meantime it probably makes sense to temporarily revert the
  commit as a SAUCE patch. Then we will drop the SAUCE patch once we'll
  have a proper fix upstream.

  [Test case]

  The following test should complete correctly without any timeout:

    pull-lp-source -d hello
    autopkgtest-buildvm-ubuntu-cloud -r noble
    autopkgtest -U hello*.dsc -- qemu ./autopkgtest-noble-amd64.img

  
  [Fix]

  Revert the following commit (until we have a proper fix upstream):

   80105ed2fd27 ("9p: Use netfslib read/write_iter")

  [Regression potential]

  We may experience other regressions related to 9pfs with this change,
  however it's quite unlikely to happen since we are reverting a commit,
  restoring the previous behavior.

  [Original bug report]

  autopkgtest-virt-qemu sometimes hangs when running tests on noble
  images. Originally reported by schopin, who also provided a
  reproducer:

    pull-lp-source -d hello
    autopkgtest-buildvm-ubuntu-cloud -r noble
    autopkgtest -U hello*.dsc -- qemu ./autopkgtest-noble-amd64.img

  I've been able to reproduce it with debugging enabled:

    autopkgtest -ddd -U hello_2.10-3.dsc -- qemu --debug --show-boot
  /path/to/image

  It can get stuck during different stages, but AFAICT always during
  "copydown" operations, log excerpts follow. It may be a coincidence,
  but this started happening around the time linux-
  image-6.8.0-11-generic (6.8.0-11.11) migrated to noble. The testbeds I
  used booted 6.6 but then rebooted into that 6.8 kernel after being
  upgraded by autopkgtest.

  -- logs --

  Removing autopkgtest-satdep (0) ...
  [...]
  autopkgtest-virt-qemu: DBG: executing copydown /tmp/autopkgtest.output.g8v75e8g/tests-tree/ /t/
  autopkgtest-virt-qemu: DBG: ['cmdls', "(['tar', '--directory', '/tmp/autopkgtest.output.g8v75e]
  autopkgtest-virt-qemu: DBG: ['srcstdin', "<_io.BufferedReader name='/dev/null'>", 'deststdout']
  autopkgtest-virt-qemu: DBG:  +< tar --directory /tmp/autopkgtest.output.g8v75e8g/tests-tree/ --
  autopkgtest-virt-qemu: DBG:  +> /tmp/autopkgtest-qemu.ztmr6f5k/runcmd sh -ec if ! test -d /tmp-
  autopkgtest-virt-qemu: DBG:  +>?

  -- or --

  autopkgtest: DBG: sending command to testbed: copydown /tmp/autopkgtest.output.c9utq3bx/tests-tree/ /tmp/autopkgtest.H8NDfW/build.DLR/src/
  autopkgtest-virt-qemu: DBG: executing copydown /tmp/autopkgtest.output.c9utq3bx/tests-tree/ /tmp/autopkgtest.H8NDfW/build.DLR/src/
  autopkgtest-virt-qemu: DBG: ['cmdls', "(['tar', '--directory', '/tmp/autopkgtest.output.c9utq3bx/tests-tree/', '--warning=none', '-c', '.', '-f', '-'], ['/tmp/autopkgtest-qemu.qtkcgg5l/runcm]
  autopkgtest-virt-qemu: DBG: ['srcstdin', "<_io.BufferedReader name='/dev/null'>", 'deststdout', "<_io.BufferedReader name='/dev/null'>", 'devnull_read', <_io.BufferedReader name='/dev/null'>]
  autopkgtest-virt-qemu: DBG:  +< tar --directory /tmp/autopkgtest.output.c9utq3bx/tests-tree/ --warning=none -c . -f -
  autopkgtest-virt-qemu: DBG:  +> /tmp/autopkgtest-qemu.qtkcgg5l/runcmd sh -ec if ! test -d /tmp/autopkgtest.H8NDfW/build.DLR/src/; then mkdir -- /tmp/autopkgtest.H8NDfW/build.DLR/src/; fi; cd-
  autopkgtest-virt-qemu: DBG:  +>?

To manage notifications about this bug go to:
https://bugs.launchpad.net/linux/+bug/2056461/+subscriptions