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    SubjectRe: [PATCH][RFC] fix kernel BUG at mm/migrate.c:719! in 2.6.26-rc5-mm3
    On Wed, 18 Jun 2008 10:54:00 +0900, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
    > On Wed, 18 Jun 2008 00:33:18 +0900, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
    > > > @@ -715,13 +725,7 @@ unlock:
    > > > * restored.
    > > > */
    > > > list_del(&page->lru);
    > > > - if (!page->mapping) {
    > > > - VM_BUG_ON(page_count(page) != 1);
    > > > - unlock_page(page);
    > > > - put_page(page); /* just free the old page */
    > > > - goto end_migration;
    > > > - } else
    > > > - unlock = putback_lru_page(page);
    > > > + unlock = putback_lru_page(page);
    > > > }
    > > >
    > > > if (unlock)
    > >
    > > this part is really necessary?
    > > I tryed to remove it, but any problem doesn't happend.
    > >
    > I made this part first, and added a fix for migration_entry_wait later.
    >
    > So, I haven't test without this part, and I think it will cause
    > VM_BUG_ON() here without this part.
    >
    > Anyway, I will test it.
    >
    I got this VM_BUG_ON() as expected only by doing:

    # echo $$ >/cgroup/cpuset/02/tasks

    So, I beleive that both fixes for migration_entry_wait and
    unmap_and_move (and, of course, removal VM_BUG_ON from
    putback_lru_page) are needed.


    Thanks,
    Daisuke Nishimura.


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