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From: NeilBrown <neilb@suse.com>
To: Andreas Dilger <adilger@dilger.ca>, Jeff Layton <jlayton@redhat.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>,
	linux-mm <linux-mm@kvack.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	lsf-pc <lsf-pc@lists.linuxfoundation.org>,
	Neil Brown <neilb@suse.de>,
	linux-scsi <linux-scsi@vger.kernel.org>,
	linux-block@vger.kernel.org
Subject: Re: [LSF/MM TOPIC] do we really need PG_error at all?
Date: Tue, 28 Feb 2017 10:32:34 +1100	[thread overview]
Message-ID: <87varvp5v1.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <DC27F5BA-BCCA-41FF-8D41-7BB99AA4DB26@dilger.ca>

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On Mon, Feb 27 2017, Andreas Dilger wrote:

>
> My thought is that PG_error is definitely useful for applications to get
> correct errors back when doing write()/sync_file_range() so that they know
> there is an error in the data that _they_ wrote, rather than receiving an
> error for data that may have been written by another thread, and in turn
> clearing the error from another thread so it *doesn't* know it had a write
> error.

It might be useful in that way, but it is not currently used that way.
Such usage would be a change in visible behaviour.

sync_file_range() calls filemap_fdatawait_range(), which calls
filemap_check_errors().
If there have been any errors in the file recently, inside or outside
the range, the latter will return an error which will propagate up.

>
> As for stray sync() clearing PG_error from underneath an application, that
> shouldn't happen since filemap_fdatawait_keep_errors() doesn't clear errors
> and is used by device flushing code (fdatawait_one_bdev(), wait_sb_inodes()).

filemap_fdatawait_keep_errors() calls __filemap_fdatawait_range() which
clears PG_error on every page.
What it doesn't do is call filemap_check_errors(), and so doesn't clear
AS_ENOSPC or AS_EIO.

NeilBrown

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  parent reply	other threads:[~2017-02-27 23:32 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-26 14:42 [LSF/MM TOPIC] do we really need PG_error at all? Jeff Layton
2017-02-26 17:10 ` James Bottomley
2017-02-26 21:03   ` NeilBrown
2017-02-26 22:43     ` Jeff Layton
2017-02-26 23:30     ` James Bottomley
2017-02-26 23:57       ` Jeff Layton
2017-02-27  0:27       ` NeilBrown
2017-02-27 15:07         ` Jeff Layton
2017-02-27 22:51           ` Andreas Dilger
2017-02-27 23:02             ` Jeff Layton
2017-02-27 23:32             ` NeilBrown [this message]
2017-02-28  1:11               ` [Lsf-pc] " Jeff Layton
2017-02-28 10:12                 ` Boaz Harrosh
2017-02-28 11:32                   ` Jeff Layton
2017-02-28 20:45                 ` NeilBrown

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