On Tue, Jun 27, 2023 at 05:23:31AM +0800, Qu Wenruo wrote:
>
>
> On 2023/6/27 01:32, Zorro Lang wrote:
> > On Mon, Jun 26, 2023 at 02:00:52PM +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
> > > $SCRATCH_MNT mount.
> > >
> > > This would fix btrfs/143 and hopefully future test cases which use dm
> > > devices.
> > >
> > > Reported-by: Filipe Manana <fdmanana@xxxxxxxx>
> > > Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
> > > ---
> > > common/btrfs | 14 ++++++++++++--
> > > 1 file changed, 12 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/common/btrfs b/common/btrfs
> > > index 175b33ae..4a02b2cc 100644
> > > --- a/common/btrfs
> > > +++ b/common/btrfs
> > > @@ -601,8 +601,18 @@ _btrfs_buffered_read_on_mirror()
> > > # The drop_caches doesn't seem to drop every pages on aarch64 with
> > > # 64K page size.
> > > # So here as another workaround, cycle mount the SCRATCH_MNT to ensure
> > > - # the cache are dropped.
> > > - _scratch_cycle_mount
> > > + # the cache are dropped, but we can not use _scratch_cycle_mount, as
> > > + # we may mount whatever dm device at SCRATCH_MNT.
> > > + # So here we grab the mounted block device and its mount options, then
> > > + # unmount and re-mount with the same device and options.
> > > + local mount_info=$(_mount | grep "$SCRATCH_MNT")
> > > + if [ -z "$mount_info" ]; then
> > > + _fail "failed to grab mount info of $SCRATCH_MNT"
> > > + fi
> > > + local dev=$(echo $mount_info | $AWK_PROG '{print $1}')
> > > + local opts=$(echo $mount_info | $AWK_PROG '{print $6}' | sed 's/[()]//g')
> >
> > The `findmnt` can help to get $dev and $opts:
> >
> > local dev=$(findmnt -n -T $SCRATCH_MNT -o SOURCE)
> > local opts=$(findmnt -n -T $SCRATCH_MNT -o OPTIONS)
> >
> > If you hope to check you can keep:
> >
> > if [ -z "$dev" -o -z "$opts" ];then
> > _fail "failed to grab mount info of $SCRATCH_MNT"
> > fi
>
> That's really helpful!
>
> >
> > > + _scratch_unmount
> > > + _mount $dev -o $opts $SCRATCH_MNT
> >
> > I'm wondering can this help that, after you get the "real" device name:
> >
> > SCRATCH_DEV=$dev _scratch_cycle_mount
>
> AFAIK we still need to specify the mount option.
>
> As it's possible previous mount is specifying certain mount option
> that's not in MOUNT_OPTIONS environment variables.
>
> E.g. mounting a specific subvolume or a temporary mount option.
>
> Thus I believe we may still need to specific the mount options.
Hmm... if the _scratch_cycle_mount doesn't support dmdust, others dmxxxx
(e.g. dmdelay, dmthin, dmerror, dmflaky) have similar problem, right?
Thanks,
Zorro
>
> Thanks,
> Qu
>
> >
> > Thanks,
> > Zorro
> >
> > > while [[ -z $( (( BASHPID % nr_mirrors == mirror )) &&
> > > exec $XFS_IO_PROG \
> > > -c "pread -b $size $offset $size" $file) ]]; do
> > > --
> > > 2.39.0
> > >
> >
>
