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Commit c5f8d995 authored by Hidetoshi Seto's avatar Hidetoshi Seto Committed by Ingo Molnar
Browse files

posixtimers, sched: Fix posix clock monotonicity 



Impact: Regression fix (against clock_gettime() backwarding bug)

This patch re-introduces a couple of functions, task_sched_runtime
and thread_group_sched_runtime, which was once removed at the
time of 2.6.28-rc1.

These functions protect the sampling of thread/process clock with
rq lock.  This rq lock is required not to update rq->clock during
the sampling.

i.e.
  The clock_gettime() may return
   ((accounted runtime before update) + (delta after update))
  that is less than what it should be.

v2 -> v3:
	- Rename static helper function __task_delta_exec()
	  to do_task_delta_exec() since -tip tree already has
	  a __task_delta_exec() of different version.

v1 -> v2:
	- Revises comments of function and patch description.
	- Add note about accuracy of thread group's runtime.

Signed-off-by: default avatarHidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: stable@kernel.org	[2.6.28.x][2.6.29.x]
LKML-Reference: <49D1CC93.4080401@jp.fujitsu.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 13b8bd0a

kernel/posix-cpu-timers.c

+4 −3
Original line number Diff line number Diff line
@@ -224,7 +224,7 @@ static int cpu_clock_sample(const clockid_t which_clock, struct task_struct *p, 
		cpu->cpu = virt_ticks(p);

		break;

	case CPUCLOCK_SCHED:

		cpu->sched = p->se.sum_exec_runtime + task_delta_exec(p);

		cpu->sched = task_sched_runtime(p);

		break;

	}

	return 0;
@@ -240,18 +240,19 @@ static int cpu_clock_sample_group(const clockid_t which_clock, 
{

	struct task_cputime cputime;



	thread_group_cputime(p, &cputime);

	switch (CPUCLOCK_WHICH(which_clock)) {

	default:

		return -EINVAL;

	case CPUCLOCK_PROF:

		thread_group_cputime(p, &cputime);

		cpu->cpu = cputime_add(cputime.utime, cputime.stime);

		break;

	case CPUCLOCK_VIRT:

		thread_group_cputime(p, &cputime);

		cpu->cpu = cputime.utime;

		break;

	case CPUCLOCK_SCHED:

		cpu->sched = cputime.sum_exec_runtime + task_delta_exec(p);

		cpu->sched = thread_group_sched_runtime(p);

		break;

	}

	return 0;

kernel/sched.c

+57 −8
Original line number Diff line number Diff line
@@ -4139,9 +4139,25 @@ DEFINE_PER_CPU(struct kernel_stat, kstat); 
EXPORT_PER_CPU_SYMBOL(kstat);



/*

 * Return any ns on the sched_clock that have not yet been banked in

 * Return any ns on the sched_clock that have not yet been accounted in

 * @p in case that task is currently running.

 *

 * Called with task_rq_lock() held on @rq.

 */

static u64 do_task_delta_exec(struct task_struct *p, struct rq *rq)

{

	u64 ns = 0;



	if (task_current(rq, p)) {

		update_rq_clock(rq);

		ns = rq->clock - p->se.exec_start;

		if ((s64)ns < 0)

			ns = 0;

	}



	return ns;

}



unsigned long long task_delta_exec(struct task_struct *p)

{

	unsigned long flags;
@@ -4149,16 +4165,49 @@ unsigned long long task_delta_exec(struct task_struct *p) 
	u64 ns = 0;



	rq = task_rq_lock(p, &flags);

	ns = do_task_delta_exec(p, rq);

	task_rq_unlock(rq, &flags);



	if (task_current(rq, p)) {

		u64 delta_exec;

	return ns;

}



		update_rq_clock(rq);

		delta_exec = rq->clock - p->se.exec_start;

		if ((s64)delta_exec > 0)

			ns = delta_exec;

/*

 * Return accounted runtime for the task.

 * In case the task is currently running, return the runtime plus current's

 * pending runtime that have not been accounted yet.

 */

unsigned long long task_sched_runtime(struct task_struct *p)

{

	unsigned long flags;

	struct rq *rq;

	u64 ns = 0;



	rq = task_rq_lock(p, &flags);

	ns = p->se.sum_exec_runtime + do_task_delta_exec(p, rq);

	task_rq_unlock(rq, &flags);



	return ns;

}



/*

 * Return sum_exec_runtime for the thread group.

 * In case the task is currently running, return the sum plus current's

 * pending runtime that have not been accounted yet.

 *

 * Note that the thread group might have other running tasks as well,

 * so the return value not includes other pending runtime that other

 * running tasks might have.

 */

unsigned long long thread_group_sched_runtime(struct task_struct *p)

{

	struct task_cputime totals;

	unsigned long flags;

	struct rq *rq;

	u64 ns;



	rq = task_rq_lock(p, &flags);

	thread_group_cputime(p, &totals);

	ns = totals.sum_exec_runtime + do_task_delta_exec(p, rq);

	task_rq_unlock(rq, &flags);



	return ns;