sched: Fix clock_gettime(CLOCK_[PROCESS/THREAD]_CPUTIME_ID) monotonicity (4036ac15) · Commits · 戴 / test

If a task has been dequeued, it has been accounted. Do not project cycles that may or may not ever be accounted to a dequeued task, as that may make clock_gettime() both inaccurate and non-monotonic. Protect update_rq_clock() from slight TSC skew while at it. Signed-off-by:

Mike Galbraith <umgwanakikbuti@gmail.com> Cc: kosaki.motohiro@jp.fujitsu.com Cc: pjt@google.com Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by:

Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1403588980.29711.11.camel@marge.simpson.net Signed-off-by:

Ingo Molnar <mingo@kernel.org>

kernel/sched/core.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -139,6 +139,8 @@ void update_rq_clock(struct rq *rq)
		return;

		delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
		if (delta < 0)
		return;
		rq->clock += delta;
		update_rq_clock_task(rq, delta);
		}
		@@ -2431,7 +2433,12 @@ static u64 do_task_delta_exec(struct task_struct p, struct rq rq)
		{
		u64 ns = 0;

		if (task_current(rq, p)) {
		/*
		* Must be ->curr _and_ ->on_rq. If dequeued, we would
		* project cycles that may never be accounted to this
		* thread, breaking clock_gettime().
		*/
		if (task_current(rq, p) && p->on_rq) {
		update_rq_clock(rq);
		ns = rq_clock_task(rq) - p->se.exec_start;
		if ((s64)ns < 0)
		@@ -2474,8 +2481,10 @@ unsigned long long task_sched_runtime(struct task_struct *p)
		* If we race with it leaving cpu, we'll take a lock. So we're correct.
		* If we race with it entering cpu, unaccounted time is 0. This is
		* indistinguishable from the read occurring a few cycles earlier.
		* If we see ->on_cpu without ->on_rq, the task is leaving, and has
		* been accounted, so we're correct here as well.
		*/
		if (!p->on_cpu)
		if (!p->on_cpu \|\| !p->on_rq)
		return p->se.sum_exec_runtime;
		#endif

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