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    Subject[PATCH 1/9] mm: rcu read lock for getting reference on pages in migration_entry_wait()
    Date
    migration_entry_wait() needs to take the rcu read lock so that page counts
    can be guaranteed to be stable after one rcu grace period.

    Signed-off-by: Michel Lespinasse <walken@google.com>
    ---
    mm/migrate.c | 3 +++
    1 files changed, 3 insertions(+), 0 deletions(-)

    diff --git a/mm/migrate.c b/mm/migrate.c
    index 666e4e6..6f3b5db 100644
    --- a/mm/migrate.c
    +++ b/mm/migrate.c
    @@ -193,6 +193,7 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
    struct page *page;

    ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
    + rcu_read_lock();
    pte = *ptep;
    if (!is_swap_pte(pte))
    goto out;
    @@ -212,11 +213,13 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
    */
    if (!get_page_unless_zero(page))
    goto out;
    + rcu_read_unlock();
    pte_unmap_unlock(ptep, ptl);
    wait_on_page_locked(page);
    put_page(page);
    return;
    out:
    + rcu_read_unlock();
    pte_unmap_unlock(ptep, ptl);
    }

    --
    1.7.3.1


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