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Date: Sat, 5 Jul 2014 03:43:44 -0700 From: tip-bot for Mike Galbraith <tipbot@...or.com> To: linux-tip-commits@...r.kernel.org Cc: linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org, torvalds@...ux-foundation.org, peterz@...radead.org, tglx@...utronix.de, umgwanakikbuti@...il.com Subject: [tip:sched/core] sched: Fix clock_gettime(CLOCK_[PROCESS/THREAD] _CPUTIME_ID) monotonicity Commit-ID: 4036ac1567834222fc763ab18e3e17df93b4eaaf Gitweb: http://git.kernel.org/tip/4036ac1567834222fc763ab18e3e17df93b4eaaf Author: Mike Galbraith <umgwanakikbuti@...il.com> AuthorDate: Tue, 24 Jun 2014 07:49:40 +0200 Committer: Ingo Molnar <mingo@...nel.org> CommitDate: Sat, 5 Jul 2014 11:17:30 +0200 sched: Fix clock_gettime(CLOCK_[PROCESS/THREAD]_CPUTIME_ID) monotonicity 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@...il.com> Cc: kosaki.motohiro@...fujitsu.com Cc: pjt@...gle.com Cc: Linus Torvalds <torvalds@...ux-foundation.org> Signed-off-by: Peter Zijlstra <peterz@...radead.org> Link: http://lkml.kernel.org/r/1403588980.29711.11.camel@marge.simpson.net Signed-off-by: Ingo Molnar <mingo@...nel.org> --- kernel/sched/core.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 866d840..e50234b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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