From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Damien Le Moal <Damien.LeMoal@wdc.com>,
Andreas Gruenbacher <agruenba@redhat.com>,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 07/13] xfs: allow merging ioends over append boundaries
Date: Fri, 28 Jun 2019 10:05:57 -0700 [thread overview]
Message-ID: <20190628170557.GB1404256@magnolia> (raw)
In-Reply-To: <20190628055143.GB27187@lst.de>
On Fri, Jun 28, 2019 at 07:51:43AM +0200, Christoph Hellwig wrote:
> On Thu, Jun 27, 2019 at 11:23:09AM -0700, Darrick J. Wong wrote:
> > On Thu, Jun 27, 2019 at 12:48:30PM +0200, Christoph Hellwig wrote:
> > > There is no real problem merging ioends that go beyond i_size into an
> > > ioend that doesn't. We just need to move the append transaction to the
> > > base ioend. Also use the opportunity to use a real error code instead
> > > of the magic 1 to cancel the transactions, and write a comment
> > > explaining the scheme.
> > >
> > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> >
> > Reading through this patch, I have a feeling it fixes the crash that
> > Zorro has been seeing occasionally with generic/475...
>
> So you think for some reason the disk i_size changes underneath and thus
> the xfs_ioend_is_append misfired vs the actual transaction allocations?
> I didn't even think of that, but using the different checks sure sounds
> dangerous. So yes, we'd either need to backport my patch, or at least
> replace the checks in xfs_ioend_can_merge with direct checks of
> io_append_trans.
That's my working theory, yes.
1. Dirty pages 0 and 2 of an empty file.
2. Writeback gets scheduled for pages 0 and 2, creating ioends A and C.
Both ioends describe writes past the on-disk isize so we allocate
transactions.
3. ioend C completes immediately, sets the ondisk isize to (3 * PAGESIZE).
4. Dirty page 1 of the file and immediately schedule writeback for it,
creating ioend B. ioend B describes a write within the on-disk isize so
we do not allocate setfilesize transaction.
5. ioend A and B complete and are sorted into the per-inode ioend
completion list. xfs_ioend_try_merge looks at ioend A, sees that ioend
can be merged with ioend B (same type, same cow status, same current
setfilesize status (which does not reflect the setfilesize status when A
was created)) and therefore decides to merge them.
6. A has a setfilesize transaction so _try_merge calls
xfs_setfilesize_ioend(ioend B, -1) to cancel ioend B's transaction, but
as we saw in (4), ioend B has no transaction and crashes.
--D
next prev parent reply other threads:[~2019-06-28 17:06 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-27 10:48 lift the xfs writepage code into iomap v2 Christoph Hellwig
2019-06-27 10:48 ` [PATCH 01/13] list.h: add list_pop and list_pop_entry helpers Christoph Hellwig
2019-06-27 20:48 ` Darrick J. Wong
2019-06-27 10:48 ` [PATCH 02/13] xfs: remove the unused xfs_count_page_state declaration Christoph Hellwig
2019-06-27 17:50 ` Darrick J. Wong
2019-06-27 10:48 ` [PATCH 03/13] xfs: fix a comment typo in xfs_submit_ioend Christoph Hellwig
2019-06-27 10:48 ` [PATCH 04/13] xfs: initialize iomap->flags in xfs_bmbt_to_iomap Christoph Hellwig
2019-06-27 20:44 ` Darrick J. Wong
2019-06-27 10:48 ` [PATCH 05/13] xfs: use a struct iomap in xfs_writepage_ctx Christoph Hellwig
2019-06-27 10:48 ` [PATCH 06/13] xfs: remove XFS_TRANS_NOFS Christoph Hellwig
2019-06-27 22:30 ` Darrick J. Wong
2019-06-28 5:37 ` Christoph Hellwig
2019-06-28 17:41 ` Darrick J. Wong
2019-06-27 10:48 ` [PATCH 07/13] xfs: allow merging ioends over append boundaries Christoph Hellwig
2019-06-27 18:23 ` Darrick J. Wong
2019-06-27 21:43 ` Luis Chamberlain
2019-06-28 2:52 ` Zorro Lang
2019-06-28 3:33 ` Darrick J. Wong
2019-06-28 5:51 ` Christoph Hellwig
2019-06-28 17:05 ` Darrick J. Wong [this message]
2019-06-27 10:48 ` [PATCH 08/13] xfs: simplify xfs_ioend_can_merge Christoph Hellwig
2019-06-27 10:48 ` [PATCH 09/13] xfs: refactor the ioend merging code Christoph Hellwig
2019-06-27 10:48 ` [PATCH 10/13] xfs: turn io_append_trans into an io_private void pointer Christoph Hellwig
2019-06-27 10:48 ` [PATCH 11/13] xfs: remove the fork fields in the writepage_ctx and ioend Christoph Hellwig
2019-06-27 10:48 ` [PATCH 12/13] iomap: move the xfs writeback code to iomap.c Christoph Hellwig
2019-06-27 10:48 ` [PATCH 13/13] iomap: add tracing for the address space operations Christoph Hellwig
2019-06-28 1:32 ` lift the xfs writepage code into iomap v2 Darrick J. Wong
2019-06-28 5:42 ` Christoph Hellwig
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