From 58e59854a3dfa9ab1fa1bcfc6324646cd77046a7 Mon Sep 17 00:00:00 2001 From: Jie Liu Date: Tue, 16 Jul 2013 13:11:16 +0800 Subject: 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:[] 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: [] xfs_vm_write_failed+0x74/0x1b0 [xfs] [] ? printk+0x4d/0x4f [] xfs_vm_write_begin+0x10d/0x170 [xfs] [] generic_file_buffered_write+0xdc/0x210 [] xfs_file_buffered_aio_write+0xf9/0x190 [xfs] [] xfs_file_aio_write+0xf3/0x160 [xfs] [] do_sync_write+0x94/0xd0 [] vfs_write+0x8f/0x160 [] ? wait_on_retry_sync_kiocb+0x50/0x50 [] sys_write+0x47/0x80 [] sysenter_do_call+0x12/0x28 ............. EIP: [] 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 Reviewed-by: Dave Chinner Reviewed-by: Mark Tinguely Signed-off-by: Jie Liu Signed-off-by: Ben Myers 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); -- cgit v0.10.2