linux-kernel - Re: [RFC][PATCH] vmscan: balance local_irq_disable() and local_irq

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20100204091938.C2C6.A69D9226@jp.fujitsu.com>
Date:	Thu,  4 Feb 2010 09:22:54 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	John Kacur <jkacur@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com, rostedt@...dmis.org,
	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan.kim@...il.com>, linux-mm@...ck.org
Subject: Re: [RFC][PATCH] vmscan: balance local_irq_disable() and  local_irq_enable()

> On Wed, Feb 3, 2010 at 9:09 PM, Steven Rostedt <rostedt@...dmis.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@...hat.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.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/