linux-kernel - Re: [RFC][PATCH] ext3: don't read inode block if the buffer has a write error

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Date:	Mon, 23 Jun 2008 20:01:46 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>, sct@...hat.com,
	adilger@....com, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org, jack@...e.cz,
	sugita <yumiko.sugita.yf@...achi.com>,
	Satoshi OSHIMA <satoshi.oshima.fk@...achi.com>
Subject: Re: [RFC][PATCH] ext3: don't read inode block if the buffer has a
 write error

On Mon, 23 Jun 2008, Andrew Morton wrote:
> > I don't know why it was done like this, or if anybody actually tested
> > any of it, but AFAIKS the best way to fix this is to simply not
> > clear any uptodate bits upon write errors.
> 
> There's a plausible-sounding reason for this behaviour which I forgot
> about three years ago.  Maybe Linus remembers?

We have to drop the data at _some_ point. Maybe some errors are transient, 
but a whole lot aren't. Jank out your USB memory stick, and those writes 
will continue fail. So you can't just keep things dirty - and that also 
implies that the buffer sure as heck isn't up-to-date either.

Yes, we could haev a "retry once or twice", but quite frankly, that has 
always been left to the low-level driver. By the time the buffer cache or 
page cache sees the error, it should be considered more than "transient", 
and the data in memory is simply not _useful_ any more.

So clearing the uptodate bit seems to be the logical thing to do. But on 
the other hand, it's probably not helping much either, so I don't 
personally care if we keep it "uptodate" - as long as the dirty bit 
doesn't get set, and as long as there is *some* way to get rid of the bad 
buffer later.

		Linus
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