[PATCH] CONFIG_BLOCK: blk_congestion_wait() fix

Don't just do nothing: it'll cause busywaits all over writeback and page
reclaim.

For now, take a fixed-length nap.  Will improve when NFS starts waking up
throttled processes.
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

include/linux/blkdev.h

 #ifndef _LINUX_BLKDEV_H
 #define _LINUX_BLKDEV_H
 
+#include <linux/sched.h>
 #include <linux/major.h>
 #include <linux/genhd.h>
 #include <linux/list.h>
@@ -848,7 +849,7 @@ void kblockd_flush(void);
 
 static inline long blk_congestion_wait(int rw, long timeout)
 {
-	return timeout;
+	return io_schedule_timeout(timeout);
 }
 
 static inline long nr_blockdev_pages(void)
@@ -856,7 +857,9 @@ static inline long nr_blockdev_pages(void)
 	return 0;
 }
 
-static inline void exit_io_context(void) {}
+static inline void exit_io_context(void)
+{
+}
 
 #endif /* CONFIG_BLOCK */