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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?

    Yes, spin_lock_irq() is equivalent to spin_lock() + irq_disable().
    Now, we already disabled irq. then, we only need spin_lock().

    So, I don't think shrink_inactive_list need any fix.


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