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    SubjectRe: 2.6.20-mm1 [kernel BUG at mm/swap.c:442]
    On Thu, 15 Feb 2007, Andrew Morton wrote:

    > I don't immediately see why that code isn't racy: the page can remain
    > in the pagevec for arbitrary amounts of time and someone can come along
    > and mlock it again. But given the ease with which you're hitting this,
    > it may not be a race.

    As long as the page is on the pagevec it should be off the LRU.
    Marking a page PageMlocked requires the page to be on the LRU. So a page
    cannot be marked PageMlocked as long as it is on the regular pagevecs.

    Somehow a page off the LRU was marked PageMlocked. Or a new anonymous page
    was allocated and marked PageMlocked and then some later processing put it
    onto the LRU?

    Maybe try_to_set_mlocked does work some havoc here.

    Could you see if this patch fixes it? This just disabled an optimization
    to set PageMlocked early.

    Index: linux-2.6.20-mm1/mm/memory.c
    --- linux-2.6.20-mm1.orig/mm/memory.c 2007-02-15 14:35:41.000000000 -0800
    +++ linux-2.6.20-mm1/mm/memory.c 2007-02-15 14:35:54.000000000 -0800
    @@ -930,6 +930,8 @@ static void try_to_set_mlocked(struct pa
    struct zone *zone;
    unsigned long flags;

    + return;
    if (!PageLRU(page) || PageMlocked(page))

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      Last update: 2007-02-15 23:43    [W:0.020 / U:26.752 seconds]
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