Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932635AbZJEMAo (ORCPT ); Mon, 5 Oct 2009 08:00:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932617AbZJEMAo (ORCPT ); Mon, 5 Oct 2009 08:00:44 -0400 Received: from www.tglx.de ([62.245.132.106]:44328 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932621AbZJEMAn (ORCPT ); Mon, 5 Oct 2009 08:00:43 -0400 Date: Mon, 5 Oct 2009 13:59:45 +0200 (CEST) From: Thomas Gleixner To: Peter Zijlstra cc: Anirban Sinha , Ingo Molnar , linux-kernel@vger.kernel.org, Darren Hart , Kaz Kylheku , Anirban Sinha Subject: Re: futex question In-Reply-To: <1254743934.26976.42.camel@twins> Message-ID: References: <20091001092218.GH15345@elte.hu> <4AC68F13.8050601@us.ibm.com> <4AC8CF32.8060108@anirban.org> <1254738974.26976.24.camel@twins> <1254743934.26976.42.camel@twins> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3929 Lines: 116 On Mon, 5 Oct 2009, Peter Zijlstra wrote: > On Mon, 2009-10-05 at 12:36 +0200, Peter Zijlstra wrote: > > On Sun, 2009-10-04 at 18:59 +0200, Thomas Gleixner wrote: > > > > > > do. It does not feel right. Currently, with or without my change, > > > > such a thing would indefinitely block other waiters on the same > > > > futex. > > > > > > Right. Which completely defeats the purpose of the robust list. Will > > > have a look tomorrow. > > > > Right, so mm_release() which is meant to destroy the old mm context > > actually does exit_robust_list(), but the problem is that it does so on > > the new mm, not the old one that got passed down to mm_release(). > > > > The other detail is that exit_robust_list() doesn't clear > > current->robust_list. > > > > The problem with the patch send my Ani is that it clears the robust > > lists before the point of no return, so on a failing execve() we'd have > > messed up the state. > > > > Making exit_robust_list() deal with an mm that is not the current mm is > > interesting indeed. > > Hmm... > > static int exec_mmap(struct mm_struct *mm) > { > struct task_struct *tsk; > struct mm_struct * old_mm, *active_mm; > > /* Notify parent that we're no longer interested in the old VM */ > tsk = current; > old_mm = current->mm; > mm_release(tsk, old_mm); > > if (old_mm) { > /* > * Make sure that if there is a core dump in progress > * for the old mm, we get out and die instead of going > * through with the exec. We must hold mmap_sem around > * checking core_state and changing tsk->mm. > */ > down_read(&old_mm->mmap_sem); > if (unlikely(old_mm->core_state)) { > up_read(&old_mm->mmap_sem); > return -EINTR; > } > } > task_lock(tsk); > active_mm = tsk->active_mm; > tsk->mm = mm; > tsk->active_mm = mm; > activate_mm(active_mm, mm); > task_unlock(tsk); > arch_pick_mmap_layout(mm); > if (old_mm) { > up_read(&old_mm->mmap_sem); > BUG_ON(active_mm != old_mm); > mm_update_next_owner(old_mm); > mmput(old_mm); > return 0; > } > mmdrop(active_mm); > return 0; > } > > Actually calls mm_release() before the flip, so the below might actually > be sufficient? Stared at the same place a minute ago :) But still I wonder if it's a good idea to silently release locks and set the state to OWNERDEAD instead of hitting the app programmer with a big clue stick in case the app holds locks when calling execve(). Thanks, tglx > --- > kernel/fork.c | 10 ++++++++-- > 1 files changed, 8 insertions(+), 2 deletions(-) > > diff --git a/kernel/fork.c b/kernel/fork.c > index 266c6af..4c20fff 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -570,12 +570,18 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm) > > /* Get rid of any futexes when releasing the mm */ > #ifdef CONFIG_FUTEX > - if (unlikely(tsk->robust_list)) > + if (unlikely(tsk->robust_list)) { > exit_robust_list(tsk); > + tsk->robust_list = NULL; > + } > #ifdef CONFIG_COMPAT > - if (unlikely(tsk->compat_robust_list)) > + if (unlikely(tsk->compat_robust_list)) { > compat_exit_robust_list(tsk); > + tsk->compat_robust_list = NULL; > + } > #endif > + if (unlikely(!list_empty(&tsk->pi_state_list))) > + exit_pi_state_list(tsk); > #endif > > /* Get rid of any cached register state */ > -- 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/