В Пн, 23/06/2014 в 12:24 +0200, Peter Zijlstra пишет:
> On Tue, Jun 17, 2014 at 05:24:22PM +0400, Kirill Tkhai wrote:
> >
> > 1)Iterate throw all of threads in the system.
>
> thru
Thanks :)
>
> > Check for all threads, not only for group leaders.
> >
> > 2)Check for p->on_rq instead of p->state and cputime.
> > Preempted task in !TASK_RUNNING state OR just
> > created task may be queued, that we want to be
> > reported too.
> >
> > 3)Use read_lock() instead of write_lock().
> > This function does not change any structures, and
> > read_lock() is enough.
> >
> > Signed-off-by: Kirill Tkhai <ktk...@parallels.com>
> > CC: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
> > CC: Mike Galbraith <umgwanakikb...@gmail.com>
> > CC: Peter Zijlstra <pet...@infradead.org>
> > CC: Ingo Molnar <mi...@kernel.org>
> > ---
> > kernel/cpu.c | 33 ++++++++++++++++++++-------------
> > 1 file changed, 20 insertions(+), 13 deletions(-)
> >
> > diff --git a/kernel/cpu.c b/kernel/cpu.c
> > index a343bde..81e2a38 100644
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@ -274,21 +274,28 @@ void clear_tasks_mm_cpumask(int cpu)
> > rcu_read_unlock();
> > }
> >
> > -static inline void check_for_tasks(int cpu)
> > +static inline void check_for_tasks(int dead_cpu)
> > {
> > - struct task_struct *p;
> > - cputime_t utime, stime;
> > + struct task_struct *g, *p;
> >
> > - write_lock_irq(&tasklist_lock);
> > - for_each_process(p) {
> > - task_cputime(p, &utime, &stime);
> > - if (task_cpu(p) == cpu && p->state == TASK_RUNNING &&
> > - (utime || stime))
> > - pr_warn("Task %s (pid = %d) is on cpu %d (state = %ld,
> > flags = %x)\n",
> > - p->comm, task_pid_nr(p), cpu,
> > - p->state, p->flags);
> > - }
> > - write_unlock_irq(&tasklist_lock);
> > + read_lock_irq(&tasklist_lock);
> > + do_each_thread(g, p) {
> > + if (!p->on_rq)
> > + continue;
> > + /*
> > + * We do the check with unlocked task_rq(p)->lock.
> > + * Order the reading to do not warn about a task,
> > + * which was running on this cpu in the past, and
> > + * it's just been woken on another cpu.
> > + */
> > + rmb();
>
> smp_rmb();
>
> > + if (task_cpu(p) != dead_cpu)
> > + continue;
>
> But because we don't have rq->lock held, we can be in the middle of a
> wakeup and miss a task.
>
> Then again, I suppose anything without rq->lock can and will miss tasks.
If we use rq->lock it's possible to move check_for_tasks() to
kernel/sched/core.c.
And we can leave TASK_RUNNING check for waking tasks. Maybe something like this?
static inline void check_for_tasks(int dead_cpu)
{
struct task_struct *g, *p;
struct rq *rq = cpu_rq(dead_cpu);
read_lock_irq(&tasklist_lock);
raw_spin_lock(&rq->lock)
do_each_thread(g, p) {
if (!p->on_rq && p->state != TASK_RUNNING)
continue;
if (task_cpu(p) != dead_cpu)
continue;
pr_warn("Task %s (pid=%d) is on cpu %d (state=%ld, flags=%x)\n",
p->comm, task_pid_nr(p), dead_cpu, p->state, p->flags);
} while_each_thread(g, p);
raw_spin_unlock(&rq->lock)
read_unlock_irq(&tasklist_lock);
}
It still does not give a 100% guarantee... Should we take p->pi_lock for every
task?
> > + pr_warn("Task %s (pid=%d) is on cpu %d (state=%ld, flags=%x)\n",
> > + p->comm, task_pid_nr(p), dead_cpu, p->state, p->flags);
> > + } while_each_thread(g, p);
> > + read_unlock_irq(&tasklist_lock);
> > }
> >
> > struct take_cpu_down_param {
> >
> >
> >
Regards,
Kirill
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