sched/wait: Introduce wait_on_bit_timeout()

Add a new wait_on_bit_timeout() helper, basically the same as
wait_on_bit() except that it also takes a 'timeout' parameter.

All the building blocks like bit_wait_timeout() and
out_of_line_wait_on_bit_timeout() are already in place so the
addition is rather simple.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: davem@davemloft.net
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1422616476-2917-2-git-send-email-johan.hedberg@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/wait.h

@@ -989,6 +989,32 @@ wait_on_bit_io(void *word, int bit, unsigned mode)
 				       mode);
 }
 
+/**
+ * wait_on_bit_timeout - wait for a bit to be cleared or a timeout elapses
+ * @word: the word being waited on, a kernel virtual address
+ * @bit: the bit of the word being waited on
+ * @mode: the task state to sleep in
+ * @timeout: timeout, in jiffies
+ *
+ * Use the standard hashed waitqueue table to wait for a bit
+ * to be cleared. This is similar to wait_on_bit(), except also takes a
+ * timeout parameter.
+ *
+ * Returned value will be zero if the bit was cleared before the
+ * @timeout elapsed, or non-zero if the @timeout elapsed or process
+ * received a signal and the mode permitted wakeup on that signal.
+ */
+static inline int
+wait_on_bit_timeout(void *word, int bit, unsigned mode, unsigned long timeout)
+{
+	might_sleep();
+	if (!test_bit(bit, word))
+		return 0;
+	return out_of_line_wait_on_bit_timeout(word, bit,
+					       bit_wait_timeout,
+					       mode, timeout);
+}
+
 /**
  * wait_on_bit_action - wait for a bit to be cleared
  * @word: the word being waited on, a kernel virtual address