From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752922AbaIKXzD (ORCPT ); Thu, 11 Sep 2014 19:55:03 -0400 Received: from homie.mail.dreamhost.com ([208.97.132.208]:54490 "EHLO homiemail-a8.g.dreamhost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751120AbaIKXzB (ORCPT ); Thu, 11 Sep 2014 19:55:01 -0400 Message-ID: <1410479618.14217.4.camel@linux-t7sj.site> Subject: Re: futex_wait_setup sleeping while atomic bug. From: Davidlohr Bueso To: Thomas Gleixner Cc: Dave Jones , Linux Kernel , Peter Zijlstra , Darren Hart Date: Thu, 11 Sep 2014 16:53:38 -0700 In-Reply-To: References: <20140911151040.GB3008@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2014-09-11 at 23:52 +0200, Thomas Gleixner wrote: > From: Thomas Gleixner > Date: Thu, 11 Sep 2014 23:44:35 +0200 > Subject: futex: Unlock hb->lock in futex_wait_requeue_pi() error path That's the second time we are bitten by bugs in when requeing, now pi. We need to reconsider some of our testing tools to stress these paths better, imo. > futex_wait_requeue_pi() calls futex_wait_setup(). If > futex_wait_setup() succeeds it returns with hb->lock held and > preemption disabled. Now the sanity check after this does: > > if (match_futex(&q.key, &key2)) { > ret = -EINVAL; > goto out_put_keys; > } > > which releases the keys but does not release hb->lock. So we happily > return to user space with hb->lock held and therefor preemption > disabled. > > Unlock hb->lock before taking the exit route. > > Reported-by: Dave "Trinity" Jones > Signed-off-by: Thomas Gleixner Reviewed-by: Davidlohr Bueso