] __fput+0xcc/0x1b0
	 [<ffffffff802a1ba6>] fput+0x16/0x20
	 [<ffffffff8029e676>] filp_close+0x56/0x90
	 [<ffffffff8029fe0d>] sys_close+0xad/0x110
	 [<ffffffff8020c41e>] system_call+0x7e/0x83

Fix the bug by removing the cancel_dirty_page() call. Tests show that
it causes no bad behaviors on various write sizes.

=== for the patient ===
Here are more detailed demonstrations of the problem.

1) the page has both PG_dirty(D)/PAGECACHE_TAG_DIRTY(d) after being written to;
   and then only PAGECACHE_TAG_DIRTY(d) remains after the file is closed.

------------------------------ screen 0 ------------------------------
[T0] root /home/wfg# cat > /test/tiny
[T1] hi
[T2] root /home/wfg#

------------------------------ screen 1 ------------------------------
[T1] root /home/wfg# echo /test/tiny > /proc/filecache
[T1] root /home/wfg# cat /proc/filecache
     # file /test/tiny
     # flags R:referenced A:active M:mmap U:uptodate D:dirty W:writeback O:owner B:buffer d:dirty w:writeback
     # idx   len     state   refcnt
     0       1       ___UD__Bd_      2
[T2] root /home/wfg# cat /proc/filecache
     # file /test/tiny
     # flags R:referenced A:active M:mmap U:uptodate D:dirty W:writeback O:owner B:buffer d:dirty w:writeback
     # idx   len     state   refcnt
     0       1       ___U___Bd_      2

2) note the non-zero 'cancelled_write_bytes' after /tmp/hi is copied.

------------------------------ screen 0 ------------------------------
[T0] root /home/wfg# echo hi > /tmp/hi
[T1] root /home/wfg# cp /tmp/hi /dev/stdin /test
[T2] hi
[T3] root /home/wfg#

------------------------------ screen 1 ------------------------------
[T1] root /proc/4397# cd /proc/`pidof cp`
[T1] root /proc/4713# cat io
     rchar: 8396
     wchar: 3
     syscr: 20
     syscw: 1
     read_bytes: 0
     write_bytes: 20480
     cancelled_write_bytes: 4096
[T2] root /proc/4713# cat io
     rchar: 8399
     wchar: 6
     syscr: 21
     syscw: 2
     read_bytes: 0
     write_bytes: 24576
     cancelled_write_bytes: 4096

//Question: the 'write_bytes' is a bit more than expected ;-)

Tested-by: Maxim Levitsky <maximlevitsky@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Reviewed-by: Chris Mason <chris.mason@oracle.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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