Re: [PATCH v1.1 1/8] generic/604: try to make race occur reliably

Zorro Lang
2024-02-27T05:15:08Z

On Mon, Feb 26, 2024 at 08:40:21PM -0800, Darrick J. Wong wrote:
> This test will occasionaly fail like so:
>
> --- /tmp/fstests/tests/generic/604.out 2024-02-03 12:08:52.349924277 -0800
> +++ /var/tmp/fstests/generic/604.out.bad 2024-02-05 04:35:55.020000000 -0800
> @@ -1,2 +1,5 @@
> QA output created by 604
> -Silence is golden
> +mount: /opt: /dev/sda4 already mounted on /opt.
> + dmesg(1) may have more information after failed mount system call.
> +mount -o usrquota,grpquota,prjquota, /dev/sda4 /opt failed
> +(see /var/tmp/fstests/generic/604.full for details)
>
> As far as I can tell, the cause of this seems to be _scratch_mount
> getting forked and exec'd before the backgrounded umount process has a
> chance to enter the kernel. When this occurs, the mount() system call
> will return -EBUSY because this isn't an attempt to make a bind mount.
> Slow things down slightly by stalling the mount by 10ms.
>
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
> v1.1: indent commit message, fix busted comment
> ---

Reviewed-by: Zorro Lang <zlang@redhat.com>

> tests/generic/604 | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/tests/generic/604 b/tests/generic/604
> index cc6a4b214f..00da56dd70 100755
> --- a/tests/generic/604
> +++ b/tests/generic/604
> @@ -24,10 +24,12 @@ _scratch_mount
> for i in $(seq 0 500); do
> $XFS_IO_PROG -f -c "pwrite 0 4K" $SCRATCH_MNT/$i >/dev/null
> done
> -# For overlayfs, avoid unmouting the base fs after _scratch_mount
> -# tries to mount the base fs
> +# For overlayfs, avoid unmouting the base fs after _scratch_mount tries to
> +# mount the base fs. Delay the mount attempt by a small amount in the hope
> +# that the mount() call will try to lock s_umount /after/ umount has already
> +# taken it.
> $UMOUNT_PROG $SCRATCH_MNT &
> -_scratch_mount
> +sleep 0.01s ; _scratch_mount
> wait
>
> echo "Silence is golden"
>