From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx132.postini.com [74.125.245.132]) by kanga.kvack.org (Postfix) with SMTP id B9AE38D0006 for ; Thu, 6 Dec 2012 14:26:40 -0500 (EST) Received: from ipb5.telenor.se (ipb5.telenor.se [195.54.127.168]) by smtprelay-b22.telenor.se (Postfix) with ESMTP id D35E7EBBF3 for ; Thu, 6 Dec 2012 20:26:38 +0100 (CET) From: "Henrik Rydberg" Date: Thu, 6 Dec 2012 20:28:45 +0100 Subject: Re: Oops in 3.7-rc8 isolate_free_pages_block() Message-ID: <20121206192845.GA599@polaris.bitmath.org> References: <20121206091744.GA1397@polaris.bitmath.org> <20121206144821.GC18547@quack.suse.cz> <20121206161934.GA17258@suse.de> <20121206175451.GC17258@suse.de> <20121206183259.GA591@polaris.bitmath.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Linus Torvalds Cc: Mel Gorman , Jan Kara , linux-mm , Linux Kernel Mailing List > Actually, looking at it some more, I think that two-liner patch had > *ANOTHER* bug. > > Because the other line seems buggy as well. > > Instead of > > end_pfn = ALIGN(pfn + pageblock_nr_pages, pageblock_nr_pages); > > I think it should be > > end_pfn = ALIGN(pfn+1, pageblock_nr_pages); > > instead. ALIGN() already aligns upwards (but the "+1" is needed in > case pfn is already at a pageblock_nr_pages boundary, at which point > ALIGN() would have just returned that same boundary. Ah, and now the two callers treat the pointers the same way. > Hmm? Mel, please confirm. And Henrik, it might be good to test that > doubly-fixed patch. Because reading the patch and trying to fix bugs > in it that way is *not* the same as actually verifying it ;) Confirmed, working. I also checked 3.6, but could not trigger the original problem there. The code also looks different, so it makes sense. To be explicit, this is what I tested on top of v3.7-rc8: --- mm/compaction.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/mm/compaction.c b/mm/compaction.c index 9eef558..ff1c483 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -713,7 +713,15 @@ static void isolate_freepages(struct zone *zone, /* Found a block suitable for isolating free pages from */ isolated = 0; - end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn); + + /* + * As pfn may not start aligned, pfn+pageblock_nr_page + * may cross a MAX_ORDER_NR_PAGES boundary and miss + * a pfn_valid check. Ensure isolate_freepages_block() + * only scans within a pageblock. + */ + end_pfn = ALIGN(pfn + 1, pageblock_nr_pages); + end_pfn = min(end_pfn, zone_end_pfn); isolated = isolate_freepages_block(cc, pfn, end_pfn, freelist, false); nr_freepages += isolated; -- 1.8.0.1 Hopefully, that's a wrap. :-) Henrik -- 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