On Mon, Sep 05, 2016 at 11:13:01AM +0200, Stanislaw Gruszka wrote:
> Currently we protect 64bit sum_exec_runtime read on 32bit cpus using
> task_rq_lock() which internally takes t->pi_lock and rq->lock. Taking
> rq->lock is not needed in this case.
I looked more at kernel/sched/ code and now I'm not sure about this.
I assumed that update_curr() is called with rq->curr->pi_lock, but
looks like it can be called with some other task->pi_lock not
necessary the rq->curr, hence looks that we need rq->lock to assure
protection
Stanislaw
> Signed-off-by: Stanislaw Gruszka <sgrus...@redhat.com>
> ---
> kernel/sched/cputime.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index b93c72d..5535774 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -315,12 +315,11 @@ static inline u64 read_sum_exec_runtime(struct
> task_struct *t)
> static u64 read_sum_exec_runtime(struct task_struct *t)
> {
> u64 ns;
> - struct rq_flags rf;
> - struct rq *rq;
> + unsigned long flags;
>
> - rq = task_rq_lock(t, &rf);
> + raw_spin_lock_irqsave(&t->pi_lock, flags);
> ns = t->se.sum_exec_runtime;
> - task_rq_unlock(rq, t, &rf);
> + raw_spin_unlock_irqrestore(&t->pi_lock, flags);
>
> return ns;
> }
> --
> 1.8.3.1
>
