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>
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@ -1516,13 +1516,26 @@ xfs_vm_write_failed(
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loff_t pos,
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unsigned len)
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{
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loff_t block_offset = pos & PAGE_MASK;
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loff_t block_offset;
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loff_t block_start;
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loff_t block_end;
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loff_t from = pos & (PAGE_CACHE_SIZE - 1);
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loff_t to = from + len;
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struct buffer_head *bh, *head;
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/*
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* The request pos offset might be 32 or 64 bit, this is all fine
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* on 64-bit platform. However, for 64-bit pos request on 32-bit
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* platform, the high 32-bit will be masked off if we evaluate the
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* block_offset via (pos & PAGE_MASK) because the PAGE_MASK is
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* 0xfffff000 as an unsigned long, hence the result is incorrect
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* which could cause the following ASSERT failed in most cases.
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* In order to avoid this, we can evaluate the block_offset of the
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* start of the page by using shifts rather than masks the mismatch
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* problem.
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*/
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block_offset = (pos >> PAGE_CACHE_SHIFT) << PAGE_CACHE_SHIFT;
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ASSERT(block_offset + from == pos);
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head = page_buffers(page);
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