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    SubjectRe: [RFC][PATCH] vmscan: balance local_irq_disable() and local_irq_enable()
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    t On Wed, 2010-02-03 at 20:53 +0100, John Kacur wrote:
    > Balance local_irq_disable() and local_irq_enable() as well as
    > spin_lock_irq() and spin_lock_unlock_irq
    >
    > Signed-off-by: John Kacur <jkacur@redhat.com>
    > ---
    > mm/vmscan.c | 3 ++-
    > 1 files changed, 2 insertions(+), 1 deletions(-)
    >
    > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > index c26986c..b895025 100644
    > --- a/mm/vmscan.c
    > +++ b/mm/vmscan.c
    > @@ -1200,8 +1200,9 @@ static unsigned long shrink_inactive_list(unsigned long max_scan,
    > if (current_is_kswapd())
    > __count_vm_events(KSWAPD_STEAL, nr_freed);
    > __count_zone_vm_events(PGSTEAL, zone, nr_freed);
    > + local_irq_enable();
    >
    > - spin_lock(&zone->lru_lock);
    > + spin_lock_irq(&zone->lru_lock);
    > /*
    > * Put back any unfreeable pages.
    > */


    The above looks wrong. I don't know the code, but just by looking at
    where the locking and interrupts are, I can take a guess.

    Lets add a little more of the code:

    local_irq_disable();
    if (current_is_kswapd())
    __count_vm_events(KSWAPD_STEAL, nr_freed);
    __count_zone_vm_events(PGSTEAL, zone, nr_freed);

    spin_lock(&zone->lru_lock);
    /*

    I'm guessing the __count_zone_vm_events and friends need interrupts
    disabled here, probably due to per cpu stuff. But if you enable
    interrupts before the spin_lock() you may let an interrupt come in and
    invalidate what was done above it.

    So no, I do not think enabling interrupts here is a good thing.

    -- Steve




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