On Thu, Jun 29, 2023 at 08:10:10AM +0800, Qu Wenruo wrote:
> [BUG]
> After commit ab41f0bddb73 ("common/btrfs: use _scratch_cycle_mount to
> ensure all page caches are dropped"), the test case btrfs/143 can fail
> like below:
>
> btrfs/143 6s ... [failed, exit status 1]- output mismatch (see ~/xfstests/results//btrfs/143.out.bad)
> --- tests/btrfs/143.out 2020-06-10 19:29:03.818519162 +0100
> +++ ~/xfstests/results//btrfs/143.out.bad 2023-06-19 17:04:00.575033899 +0100
> @@ -1,37 +1,6 @@
> QA output created by 143
> wrote 131072/131072 bytes
> XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> -XXXXXXXX: aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa
> ................
> -XXXXXXXX: aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa
> ................
> -XXXXXXXX: aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa
> ................
> -XXXXXXXX: aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa
> ................
>
> [CAUSE]
> Test case btrfs/143 uses dm-dust device to emulate read errors, this
> means we can not use _scratch_cycle_mount to cycle mount $SCRATCH_MNT.
>
> As it would go mount $SCRATCH_DEV, not the dm-dust device to
> $SCRATCH_MNT.
> This prevents us to trigger read-repair (since no error would be hit)
> thus fail the test.
>
> [FIX]
> Since we can mount whatever device at $SCRATCH_MNT, we can not use
> _scratch_cycle_mount in this case.
>
> Instead implement a small helper to grab the mounted device and its
> mount options, and use the same device and mount options to cycle
> $SCRATCH_MNT mount.
>
> This would fix btrfs/143 and hopefully future test cases which use dm
> devices.
>
> Reported-by: Filipe Manana <fdmanana@xxxxxxxx>
> Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
> ---
> Changelog:
> v2:
> - Use findmnt command to grab mount options and source device
> ---
This version looks good to me. Although the "_mount $dev -o $opts $SCRATCH_MNT"
is a little odd, but as this's a btrfs only helper, so I think it's fine for
btrfs at least.
Reviewed-by: Zorro Lang <zlang@xxxxxxxxxx>
> common/btrfs | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/common/btrfs b/common/btrfs
> index 175b33ae..0fec093d 100644
> --- a/common/btrfs
> +++ b/common/btrfs
> @@ -601,8 +601,17 @@ _btrfs_buffered_read_on_mirror()
> # The drop_caches doesn't seem to drop every pages on aarch64 with
> # 64K page size.
> # So here as another workaround, cycle mount the SCRATCH_MNT to ensure
> - # the cache are dropped.
> - _scratch_cycle_mount
> + # the cache are dropped, but we can not use _scratch_cycle_mount, as
> + # we may mount whatever dm device at SCRATCH_MNT.
> + # So here we grab the mounted block device and its mount options, then
> + # unmount and re-mount with the same device and options.
> + local dev=$(findmnt -n -T $SCRATCH_MNT -o SOURCE)
> + local opts=$(findmnt -n -T $SCRATCH_MNT -o OPTIONS)
> + if [ -z "$dev" -o -z "$opts" ]; then
> + _fail "failed to grab mount info of $SCRATCH_MNT"
> + fi
> + _scratch_unmount
> + _mount $dev -o $opts $SCRATCH_MNT
> while [[ -z $( (( BASHPID % nr_mirrors == mirror )) &&
> exec $XFS_IO_PROG \
> -c "pread -b $size $offset $size" $file) ]]; do
> --
> 2.39.0
>
