From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Subject: mm: fix crash when using XFS on loopback
The patch 8456a648cf44f ("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:
[<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 <mpatocka@xxxxxxxxxx>
Cc: John David Anglin <dave.anglin@xxxxxxxx>]
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Acked-by: Pekka Enberg <penberg@xxxxxxxxxx>
Reviewed-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Helge Deller <deller@xxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/util.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff -puN mm/util.c~mm-fix-crash-when-using-xfs-on-loopback mm/util.c
--- a/mm/util.c~mm-fix-crash-when-using-xfs-on-loopback
+++ a/mm/util.c
@@ -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;
_
--
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