sched: Add sched_class->task_dead() method

Add a new function to the scheduling class interface. It is called
at the end of a context switch, if the prev task is in TASK_DEAD state.

It will be useful for the scheduling classes that want to be notified
when one of their tasks dies, e.g. to perform some cleanup actions,
such as SCHED_DEADLINE.

Signed-off-by: Dario Faggioli <raistlin@linux.it>
Reviewed-by: Paul Turner <pjt@google.com>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>
Cc: bruce.ashfield@windriver.com
Cc: claudio@evidence.eu.com
Cc: darren@dvhart.com
Cc: dhaval.giani@gmail.com
Cc: fchecconi@gmail.com
Cc: fweisbec@gmail.com
Cc: harald.gustafsson@ericsson.com
Cc: hgu1972@gmail.com
Cc: insop.song@gmail.com
Cc: jkacur@redhat.com
Cc: johan.eker@ericsson.com
Cc: liming.wang@windriver.com
Cc: luca.abeni@unitn.it
Cc: michael@amarulasolutions.com
Cc: nicola.manica@disi.unitn.it
Cc: oleg@redhat.com
Cc: paulmck@linux.vnet.ibm.com
Cc: p.faure@akatech.ch
Cc: rostedt@goodmis.org
Cc: tommaso.cucinotta@sssup.it
Cc: vincent.guittot@linaro.org
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-2-git-send-email-juri.lelli@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -2003,6 +2003,9 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev)
 	if (unlikely(prev_state == TASK_DEAD)) {
 		task_numa_free(prev);
 
+		if (prev->sched_class->task_dead)
+			prev->sched_class->task_dead(prev);
+
 		/*
 		 * Remove function-return probe instances associated with this
 		 * task and put them back on the free list.

kernel/sched/sched.h

@@ -1023,6 +1023,7 @@ struct sched_class {
 	void (*set_curr_task) (struct rq *rq);
 	void (*task_tick) (struct rq *rq, struct task_struct *p, int queued);
 	void (*task_fork) (struct task_struct *p);
+	void (*task_dead) (struct task_struct *p);
 
 	void (*switched_from) (struct rq *this_rq, struct task_struct *task);
 	void (*switched_to) (struct rq *this_rq, struct task_struct *task);