On Tue, Jun 17, 2014 at 05:24:22PM +0400, Kirill Tkhai wrote:
>
> 1)Iterate throw all of threads in the system.
thru
> 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.
> + 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 {
>
>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
