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Date: Tue, 17 Mar 2009 15:16:32 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Cc: linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH] posixtimers: Fix posix clock monotonicity
On Tue, 17 Mar 2009 15:13:07 +0900
Hidetoshi Seto <seto.hidetoshi@...fujitsu.com> wrote:
> This patch rehires task_sched_runtime() and thread_group_sched_runtime()
> which were removed at the time of 2.6.28-rc1.
>
> These functions protect the sampling of clock with rq lock.
> This rq lock is required not to update rq->clock during the sampling.
> i.e. You may get ((banked runtime before update)+(delta after update)).
>
Does clock_gettime() go backward without lock ?
Thanks,
-Kame
> Signed-off-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
> Cc: stable@...nel.org [2.6.28.x]
>
> ---
> kernel/posix-cpu-timers.c | 7 +++--
> kernel/sched.c | 58 +++++++++++++++++++++++++++++++++++++++-----
> 2 files changed, 55 insertions(+), 10 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..617d1b8 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -4066,7 +4066,23 @@ EXPORT_PER_CPU_SYMBOL(kstat);
> /*
> * Return any ns on the sched_clock that have not yet been banked in
> * @p in case that task is currently running.
> + *
> + * Called with task_rq_lock() held on @rq.
> */
> +static u64 __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 +4090,44 @@ unsigned long long task_delta_exec(struct task_struct *p)
> u64 ns = 0;
>
> rq = task_rq_lock(p, &flags);
> + ns = __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 p->sum_exec_runtime plus any more ns on the sched_clock
> + * that have not yet been banked in case the task is currently running.
> + */
> +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 + __task_delta_exec(p, rq);
> + task_rq_unlock(rq, &flags);
> +
> + return ns;
> +}
>
> +/*
> + * Return sum_exec_runtime for the thread group plus any more ns on the
> + * sched_clock that have not yet been banked in case the task is currently
> + * running.
> + */
> +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 + __task_delta_exec(p, rq);
> task_rq_unlock(rq, &flags);
>
> return ns;
> --
> 1.6.2.1
>
> --
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