From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758841Ab2FADKU (ORCPT ); Thu, 31 May 2012 23:10:20 -0400 Received: from mga03.intel.com ([143.182.124.21]:17195 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758174Ab2FADKS (ORCPT ); Thu, 31 May 2012 23:10:18 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.71,315,1320652800"; d="scan'208";a="150227736" Date: Fri, 1 Jun 2012 11:10:15 +0800 From: Fengguang Wu To: Jan Kara Cc: Peter Zijlstra , Sasha Levin , linux-mm@kvack.org, LKML Subject: Re: [PATCH 2/2] block: Convert BDI proportion calculations to flexible proportions Message-ID: <20120601031015.GB7896@localhost> References: <1337878751-22942-1-git-send-email-jack@suse.cz> <1337878751-22942-3-git-send-email-jack@suse.cz> <1338220185.4284.19.camel@lappy> <20120529123408.GA23991@quack.suse.cz> <1338295111.26856.57.camel@twins> <20120529125452.GB23991@quack.suse.cz> <20120531221146.GA19050@quack.suse.cz> <1338503165.28384.134.camel@twins> <20120531224206.GC19050@quack.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=gb2312 Content-Disposition: inline In-Reply-To: <20120531224206.GC19050@quack.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 01, 2012 at 12:42:06AM +0200, Jan Kara wrote: > On Fri 01-06-12 00:26:05, Peter Zijlstra wrote: > > On Fri, 2012-06-01 at 00:11 +0200, Jan Kara wrote: > > > bool fprop_new_period(struct fprop_global *p, int periods) > > > { > > > - u64 events = percpu_counter_sum(&p->events); > > > + u64 events; > > > + unsigned long flags; > > > > > > + local_irq_save(flags); > > > + events = percpu_counter_sum(&p->events); > > > + local_irq_restore(flags); > > > /* > > > * Don't do anything if there are no events. > > > */ > > > @@ -73,7 +77,9 @@ bool fprop_new_period(struct fprop_global *p, int periods) > > > if (periods < 64) > > > events -= events >> periods; > > > /* Use addition to avoid losing events happening between sum and set */ > > > + local_irq_save(flags); > > > percpu_counter_add(&p->events, -events); > > > + local_irq_restore(flags); > > > p->period += periods; > > > write_seqcount_end(&p->sequence); > > > > Uhm, why bother enabling it in between? Just wrap the whole function in > > a single IRQ disable. > I wanted to have interrupts disabled for as short as possible but if you > think it doesn't matter, I'll take your advice. The result is attached. Thank you! I applied this incremental fix next to the commit "lib: Proportions with flexible period". Thanks, Fengguang > From: Jan Kara > Subject: lib: Fix possible deadlock in flexible proportion code > > When percpu counter function in fprop_new_period() is interrupted by an > interrupt while holding counter lock, it can cause deadlock when the > interrupt wants to take the lock as well. Fix the problem by disabling > interrupts when calling percpu counter functions. > > Signed-off-by: Jan Kara > > diff -u b/lib/flex_proportions.c b/lib/flex_proportions.c > --- b/lib/flex_proportions.c > +++ b/lib/flex_proportions.c > @@ -62,13 +62,18 @@ > */ > bool fprop_new_period(struct fprop_global *p, int periods) > { > - u64 events = percpu_counter_sum(&p->events); > + u64 events; > + unsigned long flags; > > + local_irq_save(flags); > + events = percpu_counter_sum(&p->events); > /* > * Don't do anything if there are no events. > */ > - if (events <= 1) > + if (events <= 1) { > + local_irq_restore(flags); > return false; > + } > write_seqcount_begin(&p->sequence); > if (periods < 64) > events -= events >> periods; > @@ -76,6 +81,7 @@ > percpu_counter_add(&p->events, -events); > p->period += periods; > write_seqcount_end(&p->sequence); > + local_irq_restore(flags); > > return true; > }