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From: Goldwyn Rodrigues <rgoldwyn@suse.de>
To: Dave Chinner <david@fromorbit.com>
Cc: darrick.wong@oracle.com, linux-btrfs@vger.kernel.org,
	fdmanana@gmail.com, linux-fsdevel@vger.kernel.org, hch@lst.de,
	linux-xfs@vger.kernel.org
Subject: Re: [PATCH 0/3] Transient errors in Direct I/O
Date: Thu, 11 Jun 2020 09:13:33 -0500	[thread overview]
Message-ID: <20200611141333.odbshenpn2zndn3a@fiona> (raw)
In-Reply-To: <20200610050510.GL2040@dread.disaster.area>

On 15:05 10/06, Dave Chinner wrote:
> On Wed, Jun 10, 2020 at 12:59:00PM +1000, Dave Chinner wrote:
> > [ Please cc the XFS list on XFS and iomap infrastructure changes.]
> > 
> > On Fri, Jun 05, 2020 at 03:48:35PM -0500, Goldwyn Rodrigues wrote:
> > > In current scenarios, for XFS, it would mean that a page invalidation
> > > would end up being a writeback error. So, if iomap returns zero, fall
> > > back to biffered I/O. XFS has never supported fallback to buffered I/O.
> > > I hope it is not "never will" ;)
> > 
> > I wouldn't say "never", but we are not going to change XFS behaviour
> > because btrfs has a page invalidation vs DIO bug in it...
> 
> Let me point out a specific "oh shit, I didn't think of that" sort
> of problem that your blind fallback to buffered IO causes. Do this
> via direct IO:
> 
> 	pwritev2(RWF_NOWAIT)
> 
> now have it fail invalidation in the direct IO path and fallback to
> buffered write. What does buffered write do with it?
> 
> 
> 	if (iocb->ki_flags & IOCB_NOWAIT)
> 		return -EOPNOTSUPP;
> 
> Yup, userspace gets a completely spurious and bogus -EOPNOTSUPP
> error to pwritev2() because some 3rd party is accessing the same
> file via mmap or buffered IO.
> 

Oh shit, I didn't think about that!

I think adding a flag to iomap_dio_rw() to return in case of page
invalidation failure is the best option for now.

-- 
Goldwyn

  reply	other threads:[~2020-06-11 14:13 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-05 20:48 Goldwyn Rodrigues
2020-06-05 20:48 ` [PATCH 1/3] iomap: dio Return zero in case of unsuccessful pagecache invalidation Goldwyn Rodrigues
2020-06-06  3:13   ` Matthew Wilcox
2020-06-05 20:48 ` [PATCH 2/3] btrfs: Wait for extent bits to release page Goldwyn Rodrigues
2020-06-08 10:20   ` Filipe Manana
2020-06-08 12:13     ` Goldwyn Rodrigues
2020-06-05 20:48 ` [PATCH 3/3] xfs: fallback to buffered I/O if direct I/O is short Goldwyn Rodrigues
2020-06-10  2:59 ` [PATCH 0/3] Transient errors in Direct I/O Dave Chinner
2020-06-10  5:05   ` Dave Chinner
2020-06-11 14:13     ` Goldwyn Rodrigues [this message]
2020-06-10  5:31 ` Qu Wenruo
2020-06-11 14:11   ` Goldwyn Rodrigues
2020-06-12 12:56     ` Qu Wenruo

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