From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261437AbVCIX0u (ORCPT ); Wed, 9 Mar 2005 18:26:50 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262092AbVCIX0t (ORCPT ); Wed, 9 Mar 2005 18:26:49 -0500 Received: from smtp203.mail.sc5.yahoo.com ([216.136.129.93]:33917 "HELO smtp203.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S262206AbVCIXZ7 (ORCPT ); Wed, 9 Mar 2005 18:25:59 -0500 Message-ID: <422F85F6.40305@yahoo.com.au> Date: Thu, 10 Mar 2005 10:25:42 +1100 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.5) Gecko/20050105 Debian/1.7.5-1 X-Accept-Language: en MIME-Version: 1.0 To: Hugh Dickins CC: Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH 11/15] ptwalk: copy_pte_range hang References: In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hugh Dickins wrote: > This patch is the odd-one-out of the sequence. The one before adjusted > copy_pte_range from a for loop to a do while loop, and it was therefore > simplest to check for lockbreak before copying pte: possibility that it > might keep getting preempted without making progress under some loads. > > Some loads such as startup: 2*HT*P4 with preemption cannot even reach > multiuser login. Suspect needs_lockbreak is broken, can get in a state > when it remains forever true. Investigate that later: for now, and for > all time, it makes sense to aim for a little progress before breaking > out; and we can manage more pte_nones than copies. > (Just to reiterate a private mail sent to Hugh earlier) Yeah I think lockbreak is broken. Because the inner spinlock never has a cond_resched_lock performed on it, so its break_lock is never set to 0, but need_lockbreak still always returns 1 for it. IMO, spin_lock should set break_lock to 0, then cond_resched_lock need not bother with it.