From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754740AbZBJSP2 (ORCPT ); Tue, 10 Feb 2009 13:15:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753833AbZBJSPS (ORCPT ); Tue, 10 Feb 2009 13:15:18 -0500 Received: from smtp-out.google.com ([216.239.45.13]:37890 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753759AbZBJSPQ (ORCPT ); Tue, 10 Feb 2009 13:15:16 -0500 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=date:from:to:cc:subject:message-id:references: mime-version:content-type:content-disposition:in-reply-to: x-operating-system:user-agent:x-system-of-record; b=ItFbpalvCWJMYRh3vJAEUUEm4Mxtq+uyR9yPibisSLfD63UIwYSmNzh25qXZrkD5D zPliGvqfnbCph64qk66qw== Date: Tue, 10 Feb 2009 10:15:04 -0800 From: Mandeep Singh Baines To: Frederic Weisbecker Cc: Ingo Molnar , linux-kernel@vger.kernel.org, rientjes@google.com, mbligh@google.com, thockin@google.com Subject: Re: [PATCH] softlockup: ensure the task has been switched out once Message-ID: <20090210181504.GI7332@google.com> References: <4991a557.1ade660a.582e.7835@mx.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4991a557.1ade660a.582e.7835@mx.google.com> X-Operating-System: Linux/2.6.18.5-gg42workstation-mixed64-32 (x86_64) User-Agent: Mutt/1.5.11 X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Frederic Weisbecker (fweisbec@gmail.com) wrote: > When we check if a task has been switched out since the last scan, we might > have a race condition on the following scenario: > > _ the task is freshly created and scheduled > _ it puts its state to TASK_UNINTERRUPTIBLE and is not yet switched out > _ check_hung_task() scans this task and will report a false positive because > t->nvcsw + t->nivcsw == t->last_switch_count == 0 > > Add a check for such cases. > > Signed-off-by: Frederic Weisbecker > --- > kernel/hung_task.c | 8 +++++++- > 1 files changed, 7 insertions(+), 1 deletions(-) > > diff --git a/kernel/hung_task.c b/kernel/hung_task.c > index 0c924de..022a492 100644 > --- a/kernel/hung_task.c > +++ b/kernel/hung_task.c > @@ -72,7 +72,13 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout) > { > unsigned long switch_count = t->nvcsw + t->nivcsw; > > - if (t->flags & PF_FROZEN) > + /* > + * Ensure the task is not frozen. > + * Also, when a freshly created task is scheduled once, changes > + * its state to TASK_UNINTERRUPTIBLE without having ever been > + * switched out once, it musn't be checked. > + */ > + if (unlikely(t->flags & PF_FROZEN || !switch_count)) > return; > > if (switch_count != t->last_switch_count) { > -- > 1.6.1 > > Looks good to me. Thanks for fixing this! Acked-by: Mandeep Singh Baines