linux-kernel - Re: SPAM: Re: SPAM: Re: [patch 2/5] mm: fault vs invalidate/truncate race fix

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Message-ID: <20061011172120.GC5259@wotan.suse.de>
Date:	Wed, 11 Oct 2006 19:21:20 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	Andrew Morton <akpm@...l.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Linux Memory Management <linux-mm@...ck.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: SPAM: Re: SPAM: Re: [patch 2/5] mm: fault vs invalidate/truncate race fix

On Wed, Oct 11, 2006 at 10:11:43AM -0700, Linus Torvalds wrote:
> 
> 
> On Wed, 11 Oct 2006, Nick Piggin wrote:
> > > 
> > > The original IO could have been started by a person who didn't have 
> > > permissions to actually carry it out successfully, so if you enter with 
> > > the page locked (because somebody else started the IO), and you wait for 
> > > the page and it's not up-to-date afterwards, you absolutely _have_ to try 
> > > the IO, and can only return a real IO error after your _own_ IO has 
> > > failed.
> > 
> > Sure, but we currently try to read _twice_, don't we?
> 
> Well, we have the read-ahead, and then the real read. By the time we do 
> the real read, we have forgotten about the read-ahead details, so..

I mean filemap_nopage does *two* synchronous reads when finding a !uptodate
page. This is despite the comment saying that it retries once on error.

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