From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760122AbZBXR3p (ORCPT ); Tue, 24 Feb 2009 12:29:45 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759670AbZBXR2W (ORCPT ); Tue, 24 Feb 2009 12:28:22 -0500 Received: from host64.cybernetics.com ([98.174.209.230]:1462 "EHLO mail.cybernetics.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759193AbZBXR2W (ORCPT ); Tue, 24 Feb 2009 12:28:22 -0500 Message-ID: <49A42E33.7020204@cybernetics.com> Date: Tue, 24 Feb 2009 12:28:19 -0500 From: Tony Battersby User-Agent: Thunderbird 2.0.0.19 (X11/20090105) MIME-Version: 1.0 To: Andrew Morton , Davide Libenzi Cc: Jonathan Corbet , linux-kernel@vger.kernel.org Subject: [PATCH 2/6] [-mm] epoll: don't use current in irq context Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ep_call_nested() (formerly ep_poll_safewake()) uses "current" to detect callback recursion, but it may be called from irq context where the use of current is generally frowned upon. It would be better to use get_cpu() and put_cpu() to detect the callback recursion. Signed-off-by: Tony Battersby --- This patch is against the current -mm tree, and might not apply to 2.6.29. Since this patch probably won't go into 2.6.29, you may apply this version of the patch after the other patches in -mm. --- a/fs/eventpoll.c 2009-02-23 13:13:33.000000000 -0500 +++ b/fs/eventpoll.c 2009-02-23 13:17:46.000000000 -0500 @@ -97,8 +97,8 @@ struct epoll_filefd { */ struct nested_call_node { struct list_head llink; - struct task_struct *task; void *cookie; + int cpu; }; /* @@ -327,7 +327,7 @@ static int ep_call_nested(struct nested_ { int error, call_nests = 0; unsigned long flags; - struct task_struct *this_task = current; + int this_cpu = get_cpu(); struct list_head *lsthead = &ncalls->tasks_call_list; struct nested_call_node *tncur; struct nested_call_node tnode; @@ -340,20 +340,19 @@ static int ep_call_nested(struct nested_ * very much limited. */ list_for_each_entry(tncur, lsthead, llink) { - if (tncur->task == this_task && + if (tncur->cpu == this_cpu && (tncur->cookie == cookie || ++call_nests > max_nests)) { /* * Ops ... loop detected or maximum nest level reached. * We abort this wake by breaking the cycle itself. */ - spin_unlock_irqrestore(&ncalls->lock, flags); - - return -1; + error = -1; + goto out_unlock; } } /* Add the current task and cookie to the list */ - tnode.task = this_task; + tnode.cpu = this_cpu; tnode.cookie = cookie; list_add(&tnode.llink, lsthead); @@ -365,8 +364,10 @@ static int ep_call_nested(struct nested_ /* Remove the current task from the list */ spin_lock_irqsave(&ncalls->lock, flags); list_del(&tnode.llink); + out_unlock: spin_unlock_irqrestore(&ncalls->lock, flags); + put_cpu(); return error; }