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    SubjectRe: [RFC][PATCH] vmscan: balance local_irq_disable() and local_irq_enable()
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    On Wed, Feb 3, 2010 at 9:09 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
    > 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.
    >

    okay, and since we have already done local_irq_disable(), then that is
    why we only need the spin_lock() and not the spin_lock_irq() flavour?
    --
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