Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754691AbaADRqG (ORCPT ); Sat, 4 Jan 2014 12:46:06 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36385 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751313AbaADRqD (ORCPT ); Sat, 4 Jan 2014 12:46:03 -0500 Date: Sat, 4 Jan 2014 12:45:45 -0500 (EST) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: Joonsoo Kim , Andi Kleen cc: Christoph Lameter , Pekka Enberg , linux-kernel@vger.kernel.org, linux-parisc@vger.kernel.org Subject: [PATCH] fix crash when using XFS on loopback Message-ID: User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4665 Lines: 105 The patch 8456a648cf44f14365f1f44de90a3da2526a4776 causes crash in the LVM2 testsuite on PA-RISC (the crashing test is fsadm.sh). The testsuite doesn't crash on 3.12, crashes on 3.13-rc1 and later. Bad Address (null pointer deref?): Code=15 regs=000000413edd89a0 (Addr=000006202224647d) CPU: 3 PID: 24008 Comm: loop0 Not tainted 3.13.0-rc6 #5 task: 00000001bf3c0048 ti: 000000413edd8000 task.ti: 000000413edd8000 YZrvWESTHLNXBCVMcbcbcbcbOGFRQPDI PSW: 00001000000001101111100100001110 Not tainted r00-03 000000ff0806f90e 00000000405c8de0 000000004013e6c0 000000413edd83f0 r04-07 00000000405a95e0 0000000000000200 00000001414735f0 00000001bf349e40 r08-11 0000000010fe3d10 0000000000000001 00000040829c7778 000000413efd9000 r12-15 0000000000000000 000000004060d800 0000000010fe3000 0000000010fe3000 r16-19 000000413edd82a0 00000041078ddbc0 0000000000000010 0000000000000001 r20-23 0008f3d0d83a8000 0000000000000000 00000040829c7778 0000000000000080 r24-27 00000001bf349e40 00000001bf349e40 202d66202224640d 00000000405a95e0 r28-31 202d662022246465 000000413edd88f0 000000413edd89a0 0000000000000001 sr00-03 000000000532c000 0000000000000000 0000000000000000 000000000532c000 sr04-07 0000000000000000 0000000000000000 0000000000000000 0000000000000000 IASQ: 0000000000000000 0000000000000000 IAOQ: 00000000401fe42c 00000000401fe430 IIR: 539c0030 ISR: 00000000202d6000 IOR: 000006202224647d CPU: 3 CR30: 000000413edd8000 CR31: 0000000000000000 ORIG_R28: 00000000405a95e0 IAOQ[0]: vma_interval_tree_iter_first+0x14/0x48 IAOQ[1]: vma_interval_tree_iter_first+0x18/0x48 RP(r2): flush_dcache_page+0x128/0x388 Backtrace: [<000000004013e6c0>] flush_dcache_page+0x128/0x388 [<0000000010fe6ca0>] lo_splice_actor+0x90/0x148 [loop] [<00000000402579b0>] splice_from_pipe_feed+0xc0/0x1d0 [<00000000402580a4>] __splice_from_pipe+0xac/0xc0 [<0000000010fe6bbc>] lo_direct_splice_actor+0x1c/0x70 [loop] [<000000004025854c>] splice_direct_to_actor+0xec/0x228 [<0000000010fe63ac>] lo_receive+0xe4/0x298 [loop] [<0000000010fe69d8>] loop_thread+0x478/0x640 [loop] [<000000004018975c>] kthread+0x134/0x168 [<000000004012c020>] end_fault_vector+0x20/0x28 [<00000000115e0098>] xfs_setsize_buftarg+0x0/0x90 [xfs] Kernel panic - not syncing: Bad Address (null pointer deref?) The patch 8456a648cf44f14365f1f44de90a3da2526a4776 changes the page structure so that the slab subsystem reuses the page->mapping field. The crash happens in the following way: * XFS allocates some memory from slab and issues a bio to read data into it. * the bio is sent to the loopback device. * lo_receive creates an actor and calls splice_direct_to_actor. * lo_splice_actor copies data to the target page. * lo_splice_actor calls flush_dcache_page because the page may be mapped by userspace. In that case we need to flush the kernel cache. * flush_dcache_page asks for the list of userspace mappings, however that page->mapping field is reused by the slab subsystem for a different purpose. This causes the crash. Note that other architectures without coherent caches (sparc, arm, mips) also call page_mapping from flush_dcache_page, so they may crash in the same way. This patch fixes this bug by testing if the page is a slab page in page_mapping and returning NULL if it is. The patch also fixes VM_BUG_ON(PageSlab(page)) that could happen in earlier kernels in the same scenario on architectures without cache coherence when CONFIG_DEBUG_VM is enabled - so it should be backported to stable kernels. In the old kernels, the function page_mapping is placed in include/linux/mm.h, so you should modify the patch accordingly when backporting it. Signed-off-by: Mikulas Patocka Cc: stable@vger.kernel.org --- mm/util.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) Index: linux-3.13-rc6/mm/util.c =================================================================== --- linux-3.13-rc6.orig/mm/util.c 2014-01-04 00:06:07.000000000 +0100 +++ linux-3.13-rc6/mm/util.c 2014-01-04 00:24:42.000000000 +0100 @@ -390,7 +390,10 @@ struct address_space *page_mapping(struc { struct address_space *mapping = page->mapping; - VM_BUG_ON(PageSlab(page)); + /* This happens if someone calls flush_dcache_page on slab page */ + if (unlikely(PageSlab(page))) + return NULL; + if (unlikely(PageSwapCache(page))) { swp_entry_t entry; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/