futex: Use freezable blocking call

Avoid waking up every thread sleeping in a futex_wait call during
suspend and resume by calling a freezable blocking call.  Previous
patches modified the freezer to avoid sending wakeups to threads
that are blocked in freezable blocking calls.

This call was selected to be converted to a freezable call because
it doesn't hold any locks or release any resources when interrupted
that might be needed by another freezing task or a kernel driver
during suspend, and is a common site where idle userspace tasks are
blocked.

Signed-off-by: Colin Cross <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: [email protected]
Cc: Tejun Heo <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Darren Hart <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Al Viro <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

kernel/futex.c

@@ -62,6 +62,7 @@
 #include <linux/ptrace.h>
 #include <linux/sched/rt.h>
 #include <linux/hugetlb.h>
+#include <linux/freezer.h>
 
 #include <asm/futex.h>
 
@@ -1808,7 +1809,7 @@ static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
 		 * is no timeout, or if it has yet to expire.
 		 */
 		if (!timeout || timeout->task)
-			schedule();
+			freezable_schedule();
 	}
 	__set_current_state(TASK_RUNNING);
 }