From: Jie Liu <jeff.liu@xxxxxxxxxx>
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@xxxxxxxxx>
Reviewed-by: Dave Chinner <david@xxxxxxxxxxxxx>
Reviewed-by: Mark Tinguely <tinguely@xxxxxxx>
Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
---
fs/xfs/xfs_aops.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 596ec71..7967086 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1516,13 +1516,26 @@ xfs_vm_write_failed(
loff_t pos,
unsigned len)
{
- loff_t block_offset = pos & PAGE_MASK;
+ loff_t block_offset;
loff_t block_start;
loff_t block_end;
loff_t from = pos & (PAGE_CACHE_SIZE - 1);
loff_t to = from + len;
struct buffer_head *bh, *head;
+ /*
+ * The request pos offset might be 32 or 64 bit, this is all fine
+ * on 64-bit platform. However, for 64-bit pos request on 32-bit
+ * platform, the high 32-bit will be masked off if we evaluate the
+ * block_offset via (pos & PAGE_MASK) because the PAGE_MASK is
+ * 0xfffff000 as an unsigned long, hence the result is incorrect
+ * which could cause the following ASSERT failed in most cases.
+ * 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.
+ */
+ block_offset = (pos >> PAGE_CACHE_SHIFT) << PAGE_CACHE_SHIFT;
+
ASSERT(block_offset + from == pos);
head = page_buffers(page);
--
1.7.9.5
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