On Tue, 2013-01-08 at 03:08 +0100, Frederic Weisbecker wrote:
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index 07912dd..bf4f72d 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -484,7 +484,7 @@ void vtime_task_switch(struct task_struct *prev)
> * vtime_account().
> */
> #ifndef __ARCH_HAS_VTIME_ACCOUNT
> -void vtime_account(struct task_struct *tsk)
> +void vtime_account_irq_enter(struct task_struct *tsk)
> {
> if (!in_interrupt()) {
> /*
> @@ -505,7 +505,7 @@ void vtime_account(struct task_struct *tsk)
> }
> vtime_account_system(tsk);
> }
> -EXPORT_SYMBOL_GPL(vtime_account);
> +EXPORT_SYMBOL_GPL(vtime_account_irq_enter);
> #endif /* __ARCH_HAS_VTIME_ACCOUNT */
> #endif /* CONFIG_VIRT_CPU_ACCOUNTING */
>
> @@ -616,41 +616,67 @@ void thread_group_cputime_adjusted(struct task_struct
> *p, cputime_t *ut, cputime
> #endif /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
>
> #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
> -static DEFINE_PER_CPU(long, last_jiffies) = INITIAL_JIFFIES;
> -
> -static cputime_t get_vtime_delta(void)
> +static cputime_t get_vtime_delta(struct task_struct *tsk)
> {
> long delta;
>
> - delta = jiffies - __this_cpu_read(last_jiffies);
> - __this_cpu_add(last_jiffies, delta);
> + delta = jiffies - tsk->prev_jiffies;
> + tsk->prev_jiffies += delta;
>
> return jiffies_to_cputime(delta);
> }
>
> -void vtime_account_system(struct task_struct *tsk)
> +static void __vtime_account_system(struct task_struct *tsk)
> {
> - cputime_t delta_cpu = get_vtime_delta();
> + cputime_t delta_cpu = get_vtime_delta(tsk);
>
> account_system_time(tsk, irq_count(), delta_cpu,
> cputime_to_scaled(delta_cpu));
> }
>
> +void vtime_account_system(struct task_struct *tsk)
> +{
> + write_seqlock(&tsk->vtime_seqlock);
> + __vtime_account_system(tsk);
__vtime_account_system() calls account_system_time()
account_system_time() calls __account_system_time()
__account_system_time() calls acct_update_integrals()
(when CONFIG_TASK_XACCT is set)
acct_update_integrals() calls task_cputime()
task_cputime() grabs t->vtime_seqlock for read
DEADLOCK
ironically the subject says *Safely* read cputime ;-)
-- Steve
> + write_sequnlock(&tsk->vtime_seqlock);
> +}
> +
> +void vtime_account_irq_exit(struct task_struct *tsk)
> +{
> + write_seqlock(&tsk->vtime_seqlock);
> + if (context_tracking_in_user())
> + tsk->prev_jiffies_whence = JIFFIES_USER;
> + __vtime_account_system(tsk);
> + write_sequnlock(&tsk->vtime_seqlock);
> +}
> +
--
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