linux-kernel - Re: [patch 3/3] mm: make read_cache

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Date:	Tue, 06 Feb 2007 19:56:00 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Nick Piggin <npiggin@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hugh@...itas.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Memory Management <linux-mm@...ck.org>,
	Linux Filesystems <linux-fsdevel@...r.kernel.org>
Subject: Re: [patch 3/3] mm: make read_cache_page synchronous

Andrew Morton wrote:
> On Tue,  6 Feb 2007 09:02:33 +0100 (CET) Nick Piggin <npiggin@...e.de> wrote:
> 
> 
>>Ensure pages are uptodate after returning from read_cache_page, which allows
>>us to cut out most of the filesystem-internal PageUptodate_NoLock calls.
> 
> 
> Normally it's good to rename functions when we change their behaviour, but
> I guess any missed (or out-of-tree) filesystems will just end up doing a
> pointless wait_on_page_locked() and will continue to work OK, yes?

Yeah.

> 
> 
>>I didn't have a great look down the call chains, but this appears to fixes 7
>>possible use-before uptodate in hfs, 2 in hfsplus, 1 in jfs, a few in ecryptfs,
>>1 in jffs2, and a possible cleared data overwritten with readpage in block2mtd.
>>All depending on whether the filler is async and/or can return with a !uptodate
>>page.
>>
>>Also, a memory leak in sys_swapon().
> 
> 
> Separate patch?

Well its fixed by virtue of read_cache_page now correctly dropping the page
refcount if it finds the page !uptodate, rather than any special logic I
added.

I can do another patch though. No problem, I'll be resending the series after
this round of feedback.

-- 
SUSE Labs, Novell Inc.
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