From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f179.google.com (mail-ob0-f179.google.com [209.85.214.179]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (not verified)) by ozlabs.org (Postfix) with ESMTPS id AEEECB6FF1 for ; Mon, 23 Apr 2012 17:10:52 +1000 (EST) Received: by mail-ob0-f179.google.com with SMTP id uo19so7505922obb.38 for ; Mon, 23 Apr 2012 00:10:52 -0700 (PDT) Date: Mon, 23 Apr 2012 00:09:35 -0700 From: Anton Vorontsov To: Andrew Morton , Oleg Nesterov Subject: [PATCH 8/9] um: Fix possible race on task->mm Message-ID: <20120423070935.GH30752@lizard> References: <20120423070641.GA27702@lizard> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <20120423070641.GA27702@lizard> Cc: linaro-kernel@lists.linaro.org, Mike Frysinger , Peter Zijlstra , user-mode-linux-devel@lists.sourceforge.net, linux-sh@vger.kernel.org, Richard Weinberger , patches@linaro.org, linux-kernel@vger.kernel.org, uclinux-dist-devel@blackfin.uclinux.org, linux-mm@kvack.org, Paul Mundt , John Stultz , KOSAKI Motohiro , Russell King , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Checking for task->mm is dangerous as ->mm might disappear (exit_mm() assigns NULL under task_lock(), so tasklist lock is not enough). We can't use get_task_mm()/mmput() pair as mmput() might sleep, so let's take the task lock while we care about its mm. Note that we should also use find_lock_task_mm() to check all process' threads for a valid mm, but for uml we'll do it in a separate patch. Signed-off-by: Anton Vorontsov --- arch/um/kernel/reboot.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/um/kernel/reboot.c b/arch/um/kernel/reboot.c index 66d754c..1411f4e 100644 --- a/arch/um/kernel/reboot.c +++ b/arch/um/kernel/reboot.c @@ -25,10 +25,13 @@ static void kill_off_processes(void) read_lock(&tasklist_lock); for_each_process(p) { - if (p->mm == NULL) + task_lock(p); + if (!p->mm) { + task_unlock(p); continue; - + } pid = p->mm->context.id.u.pid; + task_unlock(p); os_kill_ptraced_process(pid, 1); } read_unlock(&tasklist_lock); -- 1.7.9.2