sched/wait: Use freezable_schedule() when possible

Replace 'schedule(); try_to_freeze();' with a call to freezable_schedule().

Tasks calling freezable_schedule() set the PF_FREEZER_SKIP flag
before calling schedule(). Unlike tasks calling schedule();
try_to_freeze() tasks calling freezable_schedule() are not awaken by
try_to_freeze_tasks(). Instead they call try_to_freeze() when they
wake up if the freeze is still underway.

It is not a problem since sleeping tasks can't do anything which isn't
allowed for a frozen task while sleeping.

The result is a potential performance gain during freeze, since less
tasks have to be awaken.

For instance on a bare Debian vm running a 4.19 stable kernel, the
number of tasks skipped in freeze_task() went up from 12 without the
patch to 32 with the patch (out of 448), an increase of > x2.5.

Signed-off-by: Hugo Lefeuvre <hle@owl.eu.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20190207200352.GA27859@behemoth.owl.eu.com.local
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Change-Id: I1b90daf9ebc8cdfaffc5fe8fe8f1883b9588a6c6

include/linux/wait.h

@@ -332,7 +332,7 @@ do {										\
 
 #define __wait_event_freezable(wq_head, condition)				\
 	___wait_event(wq_head, condition, TASK_INTERRUPTIBLE, 0, 0,		\
-			    schedule(); try_to_freeze())
+			    freezable_schedule())
 
 /**
  * wait_event_freezable - sleep (or freeze) until a condition gets true
@@ -391,7 +391,7 @@ do {										\
 #define __wait_event_freezable_timeout(wq_head, condition, timeout)		\
 	___wait_event(wq_head, ___wait_cond_timeout(condition),			\
 		      TASK_INTERRUPTIBLE, 0, timeout,				\
-		      __ret = schedule_timeout(__ret); try_to_freeze())
+		      __ret = freezable_schedule_timeout(__ret))
 
 /*
  * like wait_event_timeout() -- except it uses TASK_INTERRUPTIBLE to avoid
@@ -612,7 +612,7 @@ do {										\
 
 #define __wait_event_freezable_exclusive(wq, condition)				\
 	___wait_event(wq, condition, TASK_INTERRUPTIBLE, 1, 0,			\
-			schedule(); try_to_freeze())
+			freezable_schedule())
 
 #define wait_event_freezable_exclusive(wq, condition)				\
 ({										\