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    Subject[PATCH 4.4 29/30] percpu: acquire pcpu_lock when updating pcpu_nr_empty_pop_pages
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Tahsin Erdogan <tahsin@google.com>

    commit 320661b08dd6f1746d5c7ab4eb435ec64b97cd45 upstream.

    Update to pcpu_nr_empty_pop_pages in pcpu_alloc() is currently done
    without holding pcpu_lock. This can lead to bad updates to the variable.
    Add missing lock calls.

    Fixes: b539b87fed37 ("percpu: implmeent pcpu_nr_empty_pop_pages and chunk->nr_populated")
    Signed-off-by: Tahsin Erdogan <tahsin@google.com>
    Signed-off-by: Tejun Heo <tj@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    mm/percpu.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    --- a/mm/percpu.c
    +++ b/mm/percpu.c
    @@ -1012,8 +1012,11 @@ area_found:
    mutex_unlock(&pcpu_alloc_mutex);
    }

    - if (chunk != pcpu_reserved_chunk)
    + if (chunk != pcpu_reserved_chunk) {
    + spin_lock_irqsave(&pcpu_lock, flags);
    pcpu_nr_empty_pop_pages -= occ_pages;
    + spin_unlock_irqrestore(&pcpu_lock, flags);
    + }

    if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW)
    pcpu_schedule_balance_work();

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