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

[Christoph Hellwig <hch@infradead.org>]

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
> ---
>  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

s/unmouting/unmounting/ ?