From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758531AbaD3Jds (ORCPT ); Wed, 30 Apr 2014 05:33:48 -0400 Received: from cantor2.suse.de ([195.135.220.15]:40686 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751983AbaD3Jdr (ORCPT ); Wed, 30 Apr 2014 05:33:47 -0400 Date: Wed, 30 Apr 2014 11:33:45 +0200 From: Jiri Bohac To: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] timer: prevent overflow in apply_slack Message-ID: <20140430093345.GA18623@midget.suse.cz> References: <20140417194215.GA10494@midget.suse.cz> <20140418152310.GA13654@midget.suse.cz> <20140429111356.GA23888@midget.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Tue, Apr 29, 2014 at 07:22:25PM +0200, Thomas Gleixner wrote: > > > + mask = (1LL << bit) - 1; > > This should be 1UL, shouldn't it? yes, good catch, thanks! On architectures with sizeof(int) < sizeof (long), the computation of mask inside apply_slack() can be undefined if the computed bit is > 32. E.g. with: expires = 0xffffe6f5 and slack = 25, we get: expires_limit = 0x20000000e bit = 33 mask = (1 << 33) - 1 /* undefined */ On x86, mask becomes 1 and and the slack is not applied properly. On s390, mask is -1, expires is set to 0 and the timer fires immediately. Signed-off-by: Jiri Bohac Suggested-by: Deborah Townsend diff --git a/kernel/timer.c b/kernel/timer.c index 87bd529..4c36c91 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -838,7 +838,7 @@ unsigned long apply_slack(struct timer_list *timer, unsigned long expires) bit = find_last_bit(&mask, BITS_PER_LONG); - mask = (1 << bit) - 1; + mask = (1UL << bit) - 1; expires_limit = expires_limit & ~(mask); -- Jiri Bohac SUSE Labs, SUSE CZ