From 03e5ac2fc3bf6f4140db0371e8bb4243b24e3e02 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Tue, 14 Jan 2014 17:56:40 -0800 Subject: [PATCH] mm: fix crash when using XFS on loopback Commit 8456a648cf44 ("slab: use struct page for slab management") causes a 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: flush_dcache_page+0x128/0x388 lo_splice_actor+0x90/0x148 [loop] splice_from_pipe_feed+0xc0/0x1d0 __splice_from_pipe+0xac/0xc0 lo_direct_splice_actor+0x1c/0x70 [loop] splice_direct_to_actor+0xec/0x228 lo_receive+0xe4/0x298 [loop] loop_thread+0x478/0x640 [loop] kthread+0x134/0x168 end_fault_vector+0x20/0x28 xfs_setsize_buftarg+0x0/0x90 [xfs] Kernel panic - not syncing: Bad Address (null pointer deref?) Commit 8456a648cf44 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: John David Anglin ] Cc: Andi Kleen Cc: Christoph Lameter Acked-by: Pekka Enberg Reviewed-by: Joonsoo Kim Cc: Helge Deller Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/util.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/mm/util.c b/mm/util.c index f7bc2096071c..808f375648e7 100644 --- a/mm/util.c +++ b/mm/util.c @@ -390,7 +390,10 @@ struct address_space *page_mapping(struct page *page) { 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; -- 2.30.2