Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756830Ab1DLJEA (ORCPT ); Tue, 12 Apr 2011 05:04:00 -0400 Received: from mail-ww0-f44.google.com ([74.125.82.44]:38014 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753523Ab1DLJD7 (ORCPT ); Tue, 12 Apr 2011 05:03:59 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:from:to:cc:in-reply-to:references:content-type:date :message-id:mime-version:x-mailer:content-transfer-encoding; b=dpUptHX7Ulk6jFYl5QLCkvwA8+ne5bwbjT64wynVRSeyo0Dks65bTqDa5dz3q/qGaI Ji+xyJ1tNXzCNt+1VAu5zGk9A+ctALB10wpWz5akSNYyYGaK/eD1dKnKZNdCr0l7MZ1x uLrycR+ZdQt3dR80v4Ps5tKevblxdOvp5lgPg= Subject: Re: [PATCH 3/4]percpu_counter: fix code for 32bit systems From: Eric Dumazet To: Shaohua Li Cc: lkml , Andrew Morton , cl@linux.com, tj@kernel.org In-Reply-To: <1302595444.3981.129.camel@sli10-conroe> References: <1302595444.3981.129.camel@sli10-conroe> Content-Type: text/plain; charset="UTF-8" Date: Tue, 12 Apr 2011 11:03:55 +0200 Message-ID: <1302599035.3233.27.camel@edumazet-laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1481 Lines: 45 Le mardi 12 avril 2011 à 16:04 +0800, Shaohua Li a écrit : > percpu_counter.counter is a 's64'. Accessing it in 32-bit system is racing. > we need some locking to protect it otherwise some very wrong value could be > accessed. > > Signed-off-by: Shaohua Li > --- > include/linux/percpu_counter.h | 43 +++++++++++++++++++++++++++++++---------- > 1 file changed, 33 insertions(+), 10 deletions(-) > > Index: linux/include/linux/percpu_counter.h > =================================================================== > --- linux.orig/include/linux/percpu_counter.h 2011-04-12 15:48:44.000000000 +0800 > +++ linux/include/linux/percpu_counter.h 2011-04-12 15:48:54.000000000 +0800 > @@ -54,7 +54,15 @@ static inline s64 percpu_counter_sum(str > > static inline s64 percpu_counter_read(struct percpu_counter *fbc) > { > +#if BITS_PER_LONG == 32 > + s64 count; > + spin_lock(&fbc->lock); > + count = fbc->count; > + spin_unlock(&fbc->lock); > + return count; > +#else > return fbc->count; > +#endif > } > Hmm... did you test this with LOCKDEP on ? You add a possible deadlock here. Hint : Some percpu_counter are used from irq context. This interface assumes caller take the appropriate locking. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/