Adding linux-fsdevel. Keeping full quote for context.
On Mon, Aug 27, 2018 at 10:12:54AM +0200, Carlos Maiolino wrote:
> Hi.
>
> On Sat, Aug 25, 2018 at 09:25:33PM -0500, Eric Sandeen wrote:
> >
> >
> > On 8/25/18 9:09 AM, Andi Kleen wrote:
> > > On Fri, Aug 24, 2018 at 07:58:05PM -0500, Eric Sandeen wrote:
> > >> On 8/24/18 6:37 PM, Andi Kleen wrote:
> > >>>
> > >>> Seen this a few times now with recent kernels:
> > >>
> > >> Hi Andi -
> > >>
> > >> Dumb question maybe, but just to be clear -
> > >> Was this an RO mount on an RO device, or something else?
> > >> What type of mount was this?
> > >
> > > Was just a normal RW partition on a normal SSD. I didn't do anything
> > > special to make it RO.
> >
> > I don't know why it shows up as RO at this point, but maybe this fixes it:
> >
> > commit b089cfd95d32638335c551651a8e00fd2c4edb0b
> > Author: Jens Axboe <axboe@xxxxxxxxx>
> > Date: Tue Aug 14 10:52:40 2018 -0600
> >
> > block: don't warn for flush on read-only device
> >
> > Don't warn for a flush issued to a read-only device. It's not strictly
> > a writable command, as it doesn't change any on-media data by itself.
> >
> > Reported-by: Stefan Agner <stefan@xxxxxxxx>
> > Fixes: 721c7fc701c7 ("block: fail op_is_write() requests to read-only partitions")
> > Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>
> This kind of 'problem' is being reported quite often now. It all started with
> commit:
>
> commit 721c7fc701c71f693307d274d2b346a1ecd4a534
> Author: Ilya Dryomov <idryomov@xxxxxxxxx>
> Date: Thu Jan 11 14:09:11 2018 +0100
>
> block: fail op_is_write() requests to read-only partitions
>
> Which basically added a generic check for RO devices into generic_make_request()
> code path, as a way to enforce ioctl(BLKROSET), so far, write requests were
> never checked.
>
>
> Then, Linus applied the following commit:
>
> commit a32e236eb93e62a0f692e79b7c3c9636689559b9
> Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Date: Fri Aug 3 12:22:09 2018 -0700
>
> Partially revert "block: fail op_is_write() requests to read-only partitions"
>
> Once a few layers like LVM, didn't expect the device to enforce RO, which kept
> writing to the device while snapshotting, even if the device has been marked as
> RO.
>
> And then came the commit mentioned by Eric:
>
> commit b089cfd95d32638335c551651a8e00fd2c4edb0b
> Author: Jens Axboe <axboe@xxxxxxxxx>
> Date: Tue Aug 14 10:52:40 2018 -0600
>
> block: don't warn for flush on read-only device
>
>
> Which relaxed the rules a bit and basically let flushes to proceed without warnings.
>
> Essentially, this isn't a XFS problem, and most likely you are using XFS on top
> of some layer like LVM, and/or using snapshots, and your underlying volume went
> read-only behind XFS for some reason.
Ok, so the blame is assigned, but the question is still how to avoid the
warning:
(1) either XFS needs to check for read only underlying more often
or
(2) the warning needs to be removed.
I assume (2) is far easier. Is (1) even possible without races?
What is preferred?
-Andi
