Messages in this thread |  | | | Date | Sat, 26 Jan 2008 22:03:56 -0800 | | From | Andrew Morton <> | | Subject | Re: [patch] mm: fix PageUptodate data race | |
> On Tue, 22 Jan 2008 05:01:14 +0100 Nick Piggin <npiggin@suse.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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