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authorDave Hansen <dave@linux.vnet.ibm.com>2010-11-11 14:05:15 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2010-11-12 07:55:31 -0800
commit8d056cb965b8fb7c53c564abf28b1962d1061cd3 (patch)
treeb422c16d0fe4f647e5c1fec990d610ec28c06a44 /mm
parent834b40380e93e36f1c9b48ec1d280cebe3d7bd8c (diff)
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mm/vfs: revalidate page->mapping in do_generic_file_read()
70 hours into some stress tests of a 2.6.32-based enterprise kernel, we ran into a NULL dereference in here: int block_is_partially_uptodate(struct page *page, read_descriptor_t *desc, unsigned long from) { ----> struct inode *inode = page->mapping->host; It looks like page->mapping was the culprit. (xmon trace is below). After closer examination, I realized that do_generic_file_read() does a find_get_page(), and eventually locks the page before calling block_is_partially_uptodate(). However, it doesn't revalidate the page->mapping after the page is locked. So, there's a small window between the find_get_page() and ->is_partially_uptodate() where the page could get truncated and page->mapping cleared. We _have_ a reference, so it can't get reclaimed, but it certainly can be truncated. I think the correct thing is to check page->mapping after the trylock_page(), and jump out if it got truncated. This patch has been running in the test environment for a month or so now, and we have not seen this bug pop up again. xmon info: 1f:mon> e cpu 0x1f: Vector: 300 (Data Access) at [c0000002ae36f770] pc: c0000000001e7a6c: .block_is_partially_uptodate+0xc/0x100 lr: c000000000142944: .generic_file_aio_read+0x1e4/0x770 sp: c0000002ae36f9f0 msr: 8000000000009032 dar: 0 dsisr: 40000000 current = 0xc000000378f99e30 paca = 0xc000000000f66300 pid = 21946, comm = bash 1f:mon> r R00 = 0025c0500000006d R16 = 0000000000000000 R01 = c0000002ae36f9f0 R17 = c000000362cd3af0 R02 = c000000000e8cd80 R18 = ffffffffffffffff R03 = c0000000031d0f88 R19 = 0000000000000001 R04 = c0000002ae36fa68 R20 = c0000003bb97b8a0 R05 = 0000000000000000 R21 = c0000002ae36fa68 R06 = 0000000000000000 R22 = 0000000000000000 R07 = 0000000000000001 R23 = c0000002ae36fbb0 R08 = 0000000000000002 R24 = 0000000000000000 R09 = 0000000000000000 R25 = c000000362cd3a80 R10 = 0000000000000000 R26 = 0000000000000002 R11 = c0000000001e7b60 R27 = 0000000000000000 R12 = 0000000042000484 R28 = 0000000000000001 R13 = c000000000f66300 R29 = c0000003bb97b9b8 R14 = 0000000000000001 R30 = c000000000e28a08 R15 = 000000000000ffff R31 = c0000000031d0f88 pc = c0000000001e7a6c .block_is_partially_uptodate+0xc/0x100 lr = c000000000142944 .generic_file_aio_read+0x1e4/0x770 msr = 8000000000009032 cr = 22000488 ctr = c0000000001e7a60 xer = 0000000020000000 trap = 300 dar = 0000000000000000 dsisr = 40000000 1f:mon> t [link register ] c000000000142944 .generic_file_aio_read+0x1e4/0x770 [c0000002ae36f9f0] c000000000142a14 .generic_file_aio_read+0x2b4/0x770 (unreliable) [c0000002ae36fb40] c0000000001b03e4 .do_sync_read+0xd4/0x160 [c0000002ae36fce0] c0000000001b153c .vfs_read+0xec/0x1f0 [c0000002ae36fd80] c0000000001b1768 .SyS_read+0x58/0xb0 [c0000002ae36fe30] c00000000000852c syscall_exit+0x0/0x40 --- Exception: c00 (System Call) at 00000080a840bc54 SP (fffca15df30) is in userspace 1f:mon> di c0000000001e7a6c c0000000001e7a6c e9290000 ld r9,0(r9) c0000000001e7a70 418200c0 beq c0000000001e7b30 # .block_is_partially_uptodate+0xd0/0x100 c0000000001e7a74 e9440008 ld r10,8(r4) c0000000001e7a78 78a80020 clrldi r8,r5,32 c0000000001e7a7c 3c000001 lis r0,1 c0000000001e7a80 812900a8 lwz r9,168(r9) c0000000001e7a84 39600001 li r11,1 c0000000001e7a88 7c080050 subf r0,r8,r0 c0000000001e7a8c 7f805040 cmplw cr7,r0,r10 c0000000001e7a90 7d6b4830 slw r11,r11,r9 c0000000001e7a94 796b0020 clrldi r11,r11,32 c0000000001e7a98 419d00a8 bgt cr7,c0000000001e7b40 # .block_is_partially_uptodate+0xe0/0x100 c0000000001e7a9c 7fa55840 cmpld cr7,r5,r11 c0000000001e7aa0 7d004214 add r8,r0,r8 c0000000001e7aa4 79080020 clrldi r8,r8,32 c0000000001e7aa8 419c0078 blt cr7,c0000000001e7b20 # .block_is_partially_uptodate+0xc0/0x100 Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Reviewed-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Rik van Riel <riel@redhat.com> Cc: <arunabal@in.ibm.com> Cc: <sbest@us.ibm.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/filemap.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 61ba5e40579..4ee2e998e93 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1029,6 +1029,9 @@ find_page:
goto page_not_up_to_date;
if (!trylock_page(page))
goto page_not_up_to_date;
+ /* Did it get truncated before we got the lock? */
+ if (!page->mapping)
+ goto page_not_up_to_date_locked;
if (!mapping->a_ops->is_partially_uptodate(page,
desc, offset))
goto page_not_up_to_date_locked;