devmem: fix kmem write bug on memory holes

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.

Signed-off-by: Wu Fengguang <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

drivers/char/mem.c

@@ -555,7 +555,7 @@ static ssize_t write_kmem(struct file * file, const char __user * buf,
 				err = -EFAULT;
 				break;
 			}
-			sz = vwrite(kbuf, (char *)p, sz);
+			vwrite(kbuf, (char *)p, sz);
 			count -= sz;
 			buf += sz;
 			virtr += sz;