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Commit e81a1d6e authored by Srivatsa Vaddagiri's avatar Srivatsa Vaddagiri Committed by Syed Rameez Mustafa
Browse files

sched: window-stats: Fix exit race 



Exiting tasks are removed from tasklist and hence at some point will
become invisible to do_each_thread/for_each_thread task iterators.
This breaks the functionality of reset_all_windows_stats() which *has*
to reset stats for *all* tasks.

This patch causes exiting tasks stats to be reset *before* they are
removed from tasklist. DONT_ACCOUNT bit in exiting task's ravg.flags
is also marked so that their remaining execution time is not accounted
in cpu busy time counters (rq->curr/prev_runnable_sum).
reset_all_windows_stats() is thus guaranteed to return with all task's
stats reset to 0.

Change-Id: I5f101156a4f958c1b3f31eb0db8cd06e621b75e9
Signed-off-by: default avatarSrivatsa Vaddagiri <vatsa@codeaurora.org>
parent f90ea88f

include/linux/sched.h

+5 −0
Original line number Original line Diff line number Diff line
@@ -2131,6 +2131,11 @@ extern void wake_up_new_task(struct task_struct *tsk); 
#endif

#endif

extern void sched_fork(struct task_struct *p);

extern void sched_fork(struct task_struct *p);

extern void sched_dead(struct task_struct *p);

extern void sched_dead(struct task_struct *p);

#if defined(CONFIG_SCHED_HMP) || defined(CONFIG_SCHED_FREQ_INPUT)

extern void sched_exit(struct task_struct *p);

#else

static inline void sched_exit(struct task_struct *p) { }

#endif





extern void proc_caches_init(void);

extern void proc_caches_init(void);

extern void flush_signals(struct task_struct *);

extern void flush_signals(struct task_struct *);

kernel/exit.c

+3 −0
Original line number Original line Diff line number Diff line
@@ -769,6 +769,9 @@ void do_exit(long code) 
	}

	}





	exit_signals(tsk);  /* sets PF_EXITING */

	exit_signals(tsk);  /* sets PF_EXITING */



	sched_exit(tsk);



	/*

	/*

	 * tsk->flags are checked in the futex code to protect against

	 * tsk->flags are checked in the futex code to protect against

	 * an exiting task cleaning up the robust pi futexes.

	 * an exiting task cleaning up the robust pi futexes.

kernel/sched/core.c

+51 −4
Original line number Original line Diff line number Diff line
@@ -1188,6 +1188,7 @@ static u64 sched_clock_at_init_jiffy; 




#define CURR_WINDOW_CONTRIB	1

#define CURR_WINDOW_CONTRIB	1

#define PREV_WINDOW_CONTRIB	2

#define PREV_WINDOW_CONTRIB	2

#define DONT_ACCOUNT		4





/* Returns how undercommitted a CPU is given its current frequency and

/* Returns how undercommitted a CPU is given its current frequency and

 * task load (as measured in the previous window).  Returns this value

 * task load (as measured in the previous window).  Returns this value
@@ -1232,7 +1233,7 @@ update_history(struct rq *rq, struct task_struct *p, u32 runtime, int samples, 
	u64 sum = 0;

	u64 sum = 0;





	if (new_window) {

	if (new_window) {

		p->ravg.flags = 0;

		p->ravg.flags &= ~(CURR_WINDOW_CONTRIB | PREV_WINDOW_CONTRIB);

		if (runtime)

		if (runtime)

			p->ravg.flags |= PREV_WINDOW_CONTRIB;

			p->ravg.flags |= PREV_WINDOW_CONTRIB;

	}

	}
@@ -1447,7 +1448,14 @@ static void update_task_ravg(struct task_struct *p, struct rq *rq, 
			new_window = 1;

			new_window = 1;

		}

		}





		if (update_sum) {

		/*

		 * Tasks marked as DONT_ACCOUNT will not be accounted in

		 * rq->prev/curr_runnable_sum. We however want to perform

		 * maintenance duties on other counters such as window_start

		 * and roll over of curr_runnable_sum into prev_runnable_sum

		 * when update_task_ravg() is called on such tasks.

		 */

		if (update_sum && !(p->ravg.flags & DONT_ACCOUNT)) {

			delta = now - mark_start;

			delta = now - mark_start;

			delta = scale_exec_time(delta, rq);

			delta = scale_exec_time(delta, rq);

			BUG_ON(delta < 0);

			BUG_ON(delta < 0);
@@ -1467,7 +1475,7 @@ static void update_task_ravg(struct task_struct *p, struct rq *rq, 




		if (nr_full_windows) {

		if (nr_full_windows) {

			window_start += nr_full_windows * window_size;

			window_start += nr_full_windows * window_size;

			if (update_sum)

			if (update_sum && !(p->ravg.flags & DONT_ACCOUNT))

				sum = window_size;

				sum = window_size;

			sum = scale_exec_time(sum, rq);

			sum = scale_exec_time(sum, rq);

			update_history(rq, p, sum, nr_full_windows,

			update_history(rq, p, sum, nr_full_windows,
@@ -1660,11 +1668,50 @@ static void reset_task_stats(struct task_struct *p) 
	p->ravg.sum = 0;

	p->ravg.sum = 0;

	p->ravg.demand = 0;

	p->ravg.demand = 0;

	p->ravg.partial_demand = 0;

	p->ravg.partial_demand = 0;

	p->ravg.flags = 0;

	p->ravg.flags &= ~(CURR_WINDOW_CONTRIB | PREV_WINDOW_CONTRIB);

	for (i = 0; i < RAVG_HIST_SIZE_MAX; ++i)

	for (i = 0; i < RAVG_HIST_SIZE_MAX; ++i)

		p->ravg.sum_history[i] = 0;

		p->ravg.sum_history[i] = 0;

}

}





/*

 * sched_exit() - Set DONT_ACCOUNT bit in task's ravg.flags

 *

 * This will remove an exiting task's stats from cpu busy counters

 * (rq->curr/prev_runnable_sum) and also reset its stats. DONT_ACCOUNT bit is

 * also set in exiting tasks ravg.flags so that its future usage of cpu is

 * discounted from cpu busy time.

 *

 * We need this so that reset_all_windows_stats() can function correctly.

 * reset_all_window_stats() depends on do_each_thread/for_each_thread task

 * iterators to reset *all* task's statistics. Exiting tasks however become

 * invisible to those iterators. sched_exit() is called on a exiting task prior

 * to being removed from task_list, which will let reset_all_window_stats()

 * function correctly.

 */

void sched_exit(struct task_struct *p)

{

	unsigned long flags;

	int cpu = get_cpu();

	struct rq *rq = cpu_rq(cpu);



	raw_spin_lock_irqsave(&rq->lock, flags);

	/* rq->curr == p */

	update_task_ravg(rq->curr, rq, TASK_UPDATE, sched_clock(), 0);

	dequeue_task(rq, p, 0);

	if (p->ravg.flags & CURR_WINDOW_CONTRIB)

		rq->curr_runnable_sum -= p->ravg.partial_demand;

	if (p->ravg.flags & PREV_WINDOW_CONTRIB)

		rq->prev_runnable_sum -= p->ravg.demand;

	BUG_ON((s64)rq->curr_runnable_sum < 0);

	BUG_ON((s64)rq->prev_runnable_sum < 0);

	reset_task_stats(p);

	p->ravg.flags |= DONT_ACCOUNT;

	enqueue_task(rq, p, 0);

	raw_spin_unlock_irqrestore(&rq->lock, flags);



	put_cpu();

}



/* Called with IRQs disabled */

/* Called with IRQs disabled */

void reset_all_window_stats(u64 window_start, unsigned int window_size)

void reset_all_window_stats(u64 window_start, unsigned int window_size)

{

{