From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f174.google.com (mail-pd0-f174.google.com [209.85.192.174]) by kanga.kvack.org (Postfix) with ESMTP id 8B6F56B0031 for ; Mon, 10 Mar 2014 11:40:19 -0400 (EDT) Received: by mail-pd0-f174.google.com with SMTP id y13so7161906pdi.19 for ; Mon, 10 Mar 2014 08:40:19 -0700 (PDT) Received: from mailout1.samsung.com (mailout1.samsung.com. [203.254.224.24]) by mx.google.com with ESMTPS id tu7si17162340pac.280.2014.03.10.08.40.17 for (version=TLSv1 cipher=RC4-MD5 bits=128/128); Mon, 10 Mar 2014 08:40:18 -0700 (PDT) Received: from epcpsbgm2.samsung.com (epcpsbgm2 [203.254.230.27]) by mailout1.samsung.com (Oracle Communications Messaging Server 7u4-24.01(7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTP id <0N2800LRH8V3OL40@mailout1.samsung.com> for linux-mm@kvack.org; Tue, 11 Mar 2014 00:40:15 +0900 (KST) From: Bartlomiej Zolnierkiewicz Subject: Re: [PATCHv2] mm/compaction: Break out of loop on !PageBuddy in isolate_freepages_block Date: Mon, 10 Mar 2014 16:40:02 +0100 Message-id: <6597669.aH5TlWtQEa@amdc1032> In-reply-to: <1394130092-25440-1-git-send-email-lauraa@codeaurora.org> References: <1394130092-25440-1-git-send-email-lauraa@codeaurora.org> MIME-version: 1.0 Content-transfer-encoding: 7Bit Content-type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Laura Abbott Cc: Andrew Morton , Mel Gorman , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim Hi, On Thursday, March 06, 2014 10:21:32 AM 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 Acked-by: Bartlomiej Zolnierkiewicz Thanks for catching & fixing this! Best regards, -- Bartlomiej Zolnierkiewicz Samsung R&D Institute Poland Samsung Electronics -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org