sched: add bit_wait_io for 3.18 ext4 backport

Excerpted from commit 743162013: "sched: Remove proliferation of
wait_on_bit() action functions"

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

2 files changed, 38 insertions, 1 deletions

diff --git a/include/linux/wait.h b/include/linux/wait.h
index c8e576022..569d33b6b 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -959,5 +959,33 @@ static inline int wait_on_bit_lock(void *word, int bit,
 		return 0;
 	return out_of_line_wait_on_bit_lock(word, bit, action, mode);
 }
-	
+
+/* 3.18 backport */
+extern int bit_wait_io(void *);
+
+/**
+ * wait_on_bit_io - wait for a bit to be cleared
+ * @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
+ *
+ * Use the standard hashed waitqueue table to wait for a bit
+ * to be cleared.  This is similar to wait_on_bit(), but calls
+ * io_schedule() instead of schedule() for the actual waiting.
+ *
+ * Returned value will be zero if the bit was cleared, or non-zero
+ * if the process received a signal and the mode permitted wakeup
+ * on that signal.
+ */
+static inline int
+wait_on_bit_io(void *word, int bit, unsigned mode)
+{
+	might_sleep();
+	if (!test_bit(bit, word))
+		return 0;
+	return out_of_line_wait_on_bit(word, bit,
+				       bit_wait_io,
+				       mode);
+}
+
 #endif
diff --git a/kernel/wait.c b/kernel/wait.c
index 6698e0c04..bca170ef3 100644
--- a/kernel/wait.c
+++ b/kernel/wait.c
@@ -287,3 +287,12 @@ wait_queue_head_t *bit_waitqueue(void *word, int bit)
 	return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
 }
 EXPORT_SYMBOL(bit_waitqueue);
+
+__sched int bit_wait_io(void *word)
+{
+	if (signal_pending_state(current->state, current))
+		return 1;
+	io_schedule();
+	return 0;
+}
+EXPORT_SYMBOL(bit_wait_io);