From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756385AbZCLWR6 (ORCPT ); Thu, 12 Mar 2009 18:17:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752352AbZCLWRt (ORCPT ); Thu, 12 Mar 2009 18:17:49 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:41187 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751599AbZCLWRs (ORCPT ); Thu, 12 Mar 2009 18:17:48 -0400 Message-ID: <49B98A07.2000004@us.ibm.com> Date: Thu, 12 Mar 2009 15:17:43 -0700 From: Darren Hart User-Agent: Thunderbird 2.0.0.19 (X11/20090105) MIME-Version: 1.0 To: Peter Zijlstra CC: linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Rusty Russell Subject: Re: [PATCH 5/6] futex: unlock before returning -EFAULT References: <20090312075349.9856.83687.stgit@Aeon> <20090312075606.9856.88729.stgit@Aeon> <1236852816.5090.117.camel@laptop> In-Reply-To: <1236852816.5090.117.camel@laptop> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra wrote: > On Thu, 2009-03-12 at 00:56 -0700, Darren Hart wrote: >> futex_lock_pi can potentially return -EFAULT with the rt_mutex held. This >> seems like the wrong thing to do as userspace should assume -EFAULT means the >> lock was not taken. Even if it could figure this out, we'd be leaving the >> pi_state->owner in an inconsistent state. This patch unlocks the rt_mutex >> prior to returning -EFAULT to userspace. > > lockdep would complain, one is not to leave the kernel with locks held. > >> Build and boot tested on a 4 way Intel x86_64 workstation. Passes basic >> pthread_mutex and PI tests out of ltp/testcases/realtime. > > You keep mentioning these tests.. makes me wonder how much of the futex > code paths they actually test. Got any coverage info on them? Right now these are tests I know the most about and I know they excercise the futex_wait, futex_wake, futex_(un)lock_pi, and futex_requeue paths via the pthread_mutex* and pthread_cond* APIs. I doubt they test the fault logic very well, and I know they don't test shared futexes. I'd really like to ramp up my efforts on the raw sys_futex tests I've been working on, but just haven't had the cycles. I suspect they will become necessary for requeue_pi however. I also think we should look at some kind of futex-debug.c infrastructure that also adds some fault-injection to test the various error paths. -- Darren > >> Signed-off-by: Darren Hart >> Cc: Thomas Gleixner >> Cc: Peter Zijlstra >> Cc: Ingo Molnar >> Cc: Rusty Russell >> --- >> >> kernel/futex.c | 7 +++++++ >> 1 files changed, 7 insertions(+), 0 deletions(-) >> >> diff --git a/kernel/futex.c b/kernel/futex.c >> index 6579912..c980a55 100644 >> --- a/kernel/futex.c >> +++ b/kernel/futex.c >> @@ -1567,6 +1567,13 @@ retry_locked: >> } >> } >> >> + /* >> + * If fixup_pi_state_owner() faulted and was unable to handle the >> + * fault, unlock it and return the fault to userspace. >> + */ >> + if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) >> + rt_mutex_unlock(&q.pi_state->pi_mutex); >> + >> /* Unqueue and drop the lock */ >> unqueue_me_pi(&q); >> >> > > -- > 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/ > -- Darren Hart IBM Linux Technology Center Real-Time Linux Team