xfs: fix assertion failure in xfs_vm_write_failed()
In xfs_vm_write_failed(), we evaluate the block_offset of pos with
PAGE_MASK which is an unsigned long. That is fine on 64-bit platforms
regardless of whether the request pos is 32-bit or 64-bit. However, on
32-bit platforms the value is 0xfffff000 and so the high 32 bits in it
will be masked off with (pos & PAGE_MASK) for a 64-bit pos.
As a result, the evaluated block_offset is incorrect which will cause
this failure ASSERT(block_offset + from == pos); and potentially pass
the wrong block to xfs_vm_kill_delalloc_range().
In this case, we can get a kernel panic if CONFIG_XFS_DEBUG is enabled:
XFS: Assertion failed: block_offset + from == pos, file: fs/xfs/xfs_aops.c, line: 1504
------------[ cut here ]------------
kernel BUG at fs/xfs/xfs_message.c:100!
invalid opcode: 0000 [#1] SMP
........
Pid: 4057, comm: mkfs.xfs Tainted: G O 3.9.0-rc2 #1
EIP: 0060:[<
f94a7e8b>] EFLAGS:
00010282 CPU: 0
EIP is at assfail+0x2b/0x30 [xfs]
EAX:
00000056 EBX:
f6ef28a0 ECX:
00000007 EDX:
f57d22a4
ESI:
1c2fb000 EDI:
00000000 EBP:
ea6b5d30 ESP:
ea6b5d1c
DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
CR0:
8005003b CR2:
094f3ff4 CR3:
2bcb4000 CR4:
000006f0
DR0:
00000000 DR1:
00000000 DR2:
00000000 DR3:
00000000
DR6:
ffff0ff0 DR7:
00000400
Process mkfs.xfs (pid: 4057, ti=
ea6b4000 task=
ea5799e0 task.ti=
ea6b4000)
Stack:
00000000 f9525c48 f951fa80 f951f96b 000005e4 ea6b5d7c f9494b34 c19b0ea2
00000066 f3d6c620 c19b0ea2 00000000 e9a91458 00001000 00000000 00000000
00000000 c15c7e89 00000000 1c2fb000 00000000 00000000 1c2fb000 00000080
Call Trace:
[<
f9494b34>] xfs_vm_write_failed+0x74/0x1b0 [xfs]
[<
c15c7e89>] ? printk+0x4d/0x4f
[<
f9494d7d>] xfs_vm_write_begin+0x10d/0x170 [xfs]
[<
c110a34c>] generic_file_buffered_write+0xdc/0x210
[<
f949b669>] xfs_file_buffered_aio_write+0xf9/0x190 [xfs]
[<
f949b7f3>] xfs_file_aio_write+0xf3/0x160 [xfs]
[<
c115e504>] do_sync_write+0x94/0xd0
[<
c115ed1f>] vfs_write+0x8f/0x160
[<
c115e470>] ? wait_on_retry_sync_kiocb+0x50/0x50
[<
c115f017>] sys_write+0x47/0x80
[<
c15d860d>] sysenter_do_call+0x12/0x28
.............
EIP: [<
f94a7e8b>] assfail+0x2b/0x30 [xfs] SS:ESP 0068:
ea6b5d1c
---[ end trace
cdd9af4f4ecab42f ]---
Kernel panic - not syncing: Fatal exception
In order to avoid this, we can evaluate the block_offset of the start
of the page by using shifts rather than masks the mismatch problem.
Thanks Dave Chinner for help finding and fixing this bug.
Reported-by: Michael L. Semon <mlsemon35@gmail.com>
Reviewed-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Signed-off-by: Ben Myers <bpm@sgi.com>