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Date: Mon, 23 Mar 2009 10:42:32 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Cc: Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
stable@...nel.org
Subject: Re: [PATCH] posixtimers: Fix posix clock monotonicity v3
On Mon, 2009-03-23 at 18:40 +0900, Hidetoshi Seto wrote:
> Impact: Regression fix (against clock_gettime() backwarding bug)
>
> This patch re-introduces a couple of function, 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: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: stable@...nel.org [2.6.28.x]
Looks good to me, thanks!
Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
> kernel/posix-cpu-timers.c | 7 +++--
> kernel/sched.c | 65 +++++++++++++++++++++++++++++++++++++++-----
> 2 files changed, 61 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
> index 4e5288a..a65641a 100644
> --- a/kernel/posix-cpu-timers.c
> +++ b/kernel/posix-cpu-timers.c
> @@ -294,7 +294,7 @@ 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;
> @@ -310,18 +310,19 @@ 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;
> diff --git a/kernel/sched.c b/kernel/sched.c
> index db66874..2674597 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -4064,9 +4064,25 @@ 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;
> @@ -4074,16 +4090,49 @@ 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;
--
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