linux-kernel - Re: [patch] mm: fix PageUptodate data race

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Date:	Sat, 26 Jan 2008 22:03:56 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nick Piggin <npiggin@...e.de>
Cc:	hugh@...itas.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] mm: fix PageUptodate data race

> On Tue, 22 Jan 2008 05:01:14 +0100 Nick Piggin <npiggin@...e.de> wrote:
> 
> After running SetPageUptodate, preceeding stores to the page contents to
> actually bring it uptodate may not be ordered with the store to set the page
> uptodate.
> 
> Therefore, another CPU which checks PageUptodate is true, then reads the
> page contents can get stale data.
> 
> Fix this by having an smp_wmb before SetPageUptodate, and smp_rmb after
> PageUptodate.
> 
> Many places that test PageUptodate, do so with the page locked, and this
> would be enough to ensure memory ordering in those places if SetPageUptodate
> were only called while the page is locked. Unfortunately that is not always
> the case for some filesystems, but it could be an idea for the future.
> 
> Also bring the handling of anonymous page uptodateness in line with that of
> file backed page management, by marking anon pages as uptodate when they _are_
> uptodate, rather than when our implementation requires that they be marked as
> such. Doing allows us to get rid of the smp_wmb's in the page copying
> functions, which were especially added for anonymous pages for an analogous
> memory ordering problem. Both file and anonymous pages are handled with the
> same barriers.
> 

So...  it's two patches in one.


What kernel is this against?  Looks like mainline.  Is it complete and
correct when applied against the large number of pending MM changes?

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