[stable] [PATCH] devmem: fix kmem write bug on memory holes

[Wu Fengguang <fengguang.wu@intel.com>]

From: Wu Fengguang <fengguang.wu@intel.com>

commit c85e9a97c4102ce2e83112da850d838cfab5ab13 upstream.

write_kmem() used to assume vwrite() always return the full buffer length.
However now vwrite() could return 0 to indicate memory hole. This creates
a bug that "buf" is not advanced accordingly.

Fix it to simply ignore the return value, hence the memory hole.

CC: Andi Kleen <andi@firstfloor.org>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Christoph Lameter <cl@linux-foundation.org>
CC: Ingo Molnar <mingo@elte.hu>
CC: Tejun Heo <tj@kernel.org>
CC: Nick Piggin <npiggin@suse.de>
CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
CC: <stable@kernel.org>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 drivers/char/mem.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- linux-2.6.32.orig/drivers/char/mem.c	2010-02-04 10:37:55.000000000 +0800
+++ linux-2.6.32/drivers/char/mem.c	2010-02-04 10:37:59.000000000 +0800
@@ -599,7 +599,7 @@ static ssize_t write_kmem(struct file * 
 					break;
 				}
 			}
-			len = vwrite(kbuf, (char *)p, len);
+			vwrite(kbuf, (char *)p, len);
 			count -= len;
 			buf += len;
 			virtr += len;