Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932551AbZJEL4j (ORCPT ); Mon, 5 Oct 2009 07:56:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932336AbZJEL4i (ORCPT ); Mon, 5 Oct 2009 07:56:38 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:51331 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932456AbZJEL4h (ORCPT ); Mon, 5 Oct 2009 07:56:37 -0400 Subject: Re: futex question From: Peter Zijlstra To: Thomas Gleixner Cc: Anirban Sinha , Ingo Molnar , linux-kernel@vger.kernel.org, Darren Hart , Kaz Kylheku , Anirban Sinha In-Reply-To: <1254738974.26976.24.camel@twins> References: <20091001092218.GH15345@elte.hu> <4AC68F13.8050601@us.ibm.com> <4AC8CF32.8060108@anirban.org> <1254738974.26976.24.camel@twins> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Mon, 05 Oct 2009 13:58:54 +0200 Message-Id: <1254743934.26976.42.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3422 Lines: 105 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? --- 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/