From: Filipe Manana <fdmanana@kernel.org>
To: "Марк Коренберг" <socketpair@gmail.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: Major bug in BTRFS (syncs are ignored with libaio or io_uring)
Date: Fri, 11 Nov 2022 12:01:21 +0000 [thread overview]
Message-ID: <CAL3q7H4HyaTy802=YffnboKTEN2KdGmLX3z=g=HfABy2rtZLYQ@mail.gmail.com> (raw)
In-Reply-To: <CAL3q7H7RmDV2Xe2+Fb11Jr=NqPWQtw9V=En6JR1swS6Ocr5Z-w@mail.gmail.com>
On Fri, Oct 28, 2022 at 11:23 AM Filipe Manana <fdmanana@kernel.org> wrote:
>
> On Thu, Oct 27, 2022 at 11:08 PM Марк Коренберг <socketpair@gmail.com> wrote:
> >
> > How to reproduce (I tested in kernel 6.1):
> >
> > 2. mkfs.btrfs over a partition.
> > 3. mount -o lazytime,noatime
> > 4. touch file.dat
> > 5. chattr +C file.dat # turns off compression, checksumming and COW
> > 6. fallocate -l1G file.dat
> > 7. # prefill the file with random data
> > fio -ioengine=psync -name=test -bs=1M
> > -rw=write -filename=file.dat
> > 8. fio -ioengine=psync -sync=1 -direct=1 -name=test -bs=4k
> > -rw=randwrite -runtime=60 -filename=file.dat # Will show, say, 2K
> > IOPs
> > 9. fio -ioengine=io_uring -sync=1 -direct=1 -name=test -bs=4k
> > -rw=randwrite -runtime=60 -filename=file.dat # Will show, say, 32K
> > IOPs
> > 10. fio -ioengine=libaio -sync=1 -direct=1 -name=test -bs=4k
> > -rw=randwrite -runtime=60 -filename=file.dat # Will show, say, 32K
> > IOPs
> >
> > Steps 9 and 10 show implausible IOPs.
> >
> > This does not happen on, say, Ext4 (all the methods give roughly the same IOPs).
> >
> > Removing -sync=1 on all engines on Ext4 gives immediate return (as
> > expected because everything gets merged and finally written very fast)
> >
> > Adding/Removing -sync=1 with io_uring or libaio changes nothing on
> > BTRFS (it's definitely a bug)
>
> I confirm that the syncing is not happening often when using aio
> (either old aio or io_uring).
> I understand why it's happening, so I'll work on a fix for that.
Btw, I forgot to follow up, but the fix is already in Linus' tree:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8184620ae21213d51eaf2e0bd4186baacb928172
It was also backported to the 6.0.8 and 5.15.78 stable releases.
Thanks.
>
> Thanks for the report.
>
> >
> >
> > I consider it's a bug in BTRFS. Very important bug because BTRFS
> > becomes default FS in Fedora server/desktop now. This bug may cause
> > data loss. That's why I set this bug as high priority.
> >
> >
> > *****************
> > https://bugzilla.redhat.com/show_bug.cgi?id=2117971
> > *****************
> >
> >
> > --
> > Segmentation fault
prev parent reply other threads:[~2022-11-11 12:02 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-27 21:21 Major bug in BTRFS (syncs are ignored with libaio or io_uring) Марк Коренберг
2022-10-28 4:30 ` Andrei Borzenkov
2022-10-28 4:48 ` Марк Коренберг
2022-10-28 10:23 ` Filipe Manana
2022-11-11 12:01 ` Filipe Manana [this message]
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