From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752306AbaCGC7J (ORCPT ); Thu, 6 Mar 2014 21:59:09 -0500 Received: from LGEMRELSE6Q.lge.com ([156.147.1.121]:56523 "EHLO lgemrelse6q.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752083AbaCGC6y (ORCPT ); Thu, 6 Mar 2014 21:58:54 -0500 X-Original-SENDERIP: 10.177.222.157 X-Original-MAILFROM: minchan@kernel.org Date: Fri, 7 Mar 2014 11:58:52 +0900 From: Minchan Kim To: Laura Abbott Cc: Andrew Morton , Mel Gorman , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim Subject: Re: [PATCHv2] mm/compaction: Break out of loop on !PageBuddy in isolate_freepages_block Message-ID: <20140307025852.GC3787@bbox> References: <1394130092-25440-1-git-send-email-lauraa@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1394130092-25440-1-git-send-email-lauraa@codeaurora.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 06, 2014 at 10:21:32AM -0800, Laura Abbott wrote: > We received several reports of bad page state when freeing CMA pages > previously allocated with alloc_contig_range: > > <1>[ 1258.084111] BUG: Bad page state in process Binder_A pfn:63202 > <1>[ 1258.089763] page:d21130b0 count:0 mapcount:1 mapping: (null) index:0x7dfbf > <1>[ 1258.096109] page flags: 0x40080068(uptodate|lru|active|swapbacked) > > Based on the page state, it looks like the page was still in use. The page > flags do not make sense for the use case though. Further debugging showed > that despite alloc_contig_range returning success, at least one page in the > range still remained in the buddy allocator. > > There is an issue with isolate_freepages_block. In strict mode (which CMA > uses), if any pages in the range cannot be isolated, > isolate_freepages_block should return failure 0. The current check keeps > track of the total number of isolated pages and compares against the size > of the range: > > if (strict && nr_strict_required > total_isolated) > total_isolated = 0; > > After taking the zone lock, if one of the pages in the range is not > in the buddy allocator, we continue through the loop and do not > increment total_isolated. If in the last iteration of the loop we isolate > more than one page (e.g. last page needed is a higher order page), the > check for total_isolated may pass and we fail to detect that a page was > skipped. The fix is to bail out if the loop immediately if we are in > strict mode. There's no benfit to continuing anyway since we need all > pages to be isolated. Additionally, drop the error checking based on > nr_strict_required and just check the pfn ranges. This matches with > what isolate_freepages_range does. > > Signed-off-by: Laura Abbott Nice catch! stable stuff? Acked-by: Minchan Kim -- Kind regards, Minchan Kim