From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f182.google.com (mail-pd0-f182.google.com [209.85.192.182]) by kanga.kvack.org (Postfix) with ESMTP id CD5366B006C for ; Mon, 4 May 2015 05:41:23 -0400 (EDT) Received: by pdbqa5 with SMTP id qa5so158436106pdb.1 for ; Mon, 04 May 2015 02:41:23 -0700 (PDT) Received: from xiaomi.com (outboundhk.mxmail.xiaomi.com. [207.226.244.122]) by mx.google.com with ESMTPS id on8si17784230pac.235.2015.05.04.02.41.22 for (version=TLSv1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 04 May 2015 02:41:23 -0700 (PDT) From: Hui Zhu Subject: [PATCH] CMA: page_isolation: check buddy before access it Date: Mon, 4 May 2015 17:41:17 +0800 Message-ID: <1430732477-16977-1-git-send-email-zhuhui@xiaomi.com> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: akpm@linux-foundation.org, vbabka@suse.cz, iamjoonsoo.kim@lge.com, lauraa@codeaurora.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: teawater@gmail.com, Hui Zhu I got a issue: [ 214.294917] Unable to handle kernel NULL pointer dereference at virtual address 0000082a [ 214.303013] pgd = cc970000 [ 214.305721] [0000082a] *pgd=00000000 [ 214.309316] Internal error: Oops: 5 [#1] PREEMPT SMP ARM [ 214.335704] PC is at get_pageblock_flags_group+0x5c/0xb0 [ 214.341030] LR is at unset_migratetype_isolate+0x148/0x1b0 [ 214.346523] pc : [] lr : [] psr: 80000093 [ 214.346523] sp : c7029d00 ip : 00000105 fp : c7029d1c [ 214.358005] r10: 00000001 r9 : 0000000a r8 : 00000004 [ 214.363231] r7 : 60000013 r6 : 000000a4 r5 : c0a357e4 r4 : 00000000 [ 214.369761] r3 : 00000826 r2 : 00000002 r1 : 00000000 r0 : 0000003f [ 214.376291] Flags: Nzcv IRQs off FIQs on Mode SVC_32 ISA ARM Segment user [ 214.383516] Control: 10c5387d Table: 2cb7006a DAC: 00000015 [ 214.949720] Backtrace: [ 214.952192] [] (get_pageblock_flags_group+0x0/0xb0) from [] (unset_migratetype_isolate+0x148/0x1b0) [ 214.962978] r7:60000013 r6:c0a357c0 r5:c0a357e4 r4:c1555000 [ 214.968693] [] (unset_migratetype_isolate+0x0/0x1b0) from [] (undo_isolate_page_range+0xd0/0xdc) [ 214.979222] [] (undo_isolate_page_range+0x0/0xdc) from [] (__alloc_contig_range+0x254/0x34c) [ 214.989398] r9:000abc00 r8:c7028000 r7:000b1f53 r6:000b3e00 r5:00000005 r4:c7029db4 [ 214.997308] [] (__alloc_contig_range+0x0/0x34c) from [] (alloc_contig_range+0x14/0x18) [ 215.006973] [] (alloc_contig_range+0x0/0x18) from [] (dma_alloc_from_contiguous_addr+0x1ac/0x304) This issue is because when call unset_migratetype_isolate to unset a part of CMA memory, it try to access the buddy page to get its status: if (order >= pageblock_order) { page_idx = page_to_pfn(page) & ((1 << MAX_ORDER) - 1); buddy_idx = __find_buddy_index(page_idx, order); buddy = page + (buddy_idx - page_idx); if (!is_migrate_isolate_page(buddy)) { But the begin addr of this part of CMA memory is very close to a part of memory that is reserved in the boot time (not in buddy system). So add a check before access it. Signed-off-by: Hui Zhu --- mm/page_isolation.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/page_isolation.c b/mm/page_isolation.c index 755a42c..434730b 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -101,7 +101,8 @@ void unset_migratetype_isolate(struct page *page, unsigned migratetype) buddy_idx = __find_buddy_index(page_idx, order); buddy = page + (buddy_idx - page_idx); - if (!is_migrate_isolate_page(buddy)) { + if (!pfn_present(page_to_pfn(buddy)) + || !is_migrate_isolate_page(buddy)) { __isolate_free_page(page, order); kernel_map_pages(page, (1 << order), 1); set_page_refcounted(page); -- 1.9.1 -- 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