Re: [PATCH 10/11] sched: Debug nested sleeps

Peter Zijlstra
2014-09-30T13:49:36Z

On Tue, Sep 30, 2014 at 12:13:44AM +0200, Oleg Nesterov wrote:
> On 09/24, Peter Zijlstra wrote:
> >
> > +#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
> > +
> > +#define __set_task_state(tsk, state_value) \
> > + do { \
> > + (tsk)->task_state_change = _THIS_IP_; \
> > + (tsk)->state = (state_value); \
> > + } while (0)
>
> ...
>
> > @@ -7143,6 +7143,19 @@ void __might_sleep(const char *file, int
> > {
> > static unsigned long prev_jiffy; /* ratelimiting */
> >
> > + /*
> > + * Blocking primitives will set (and therefore destroy) current->state,
> > + * since we will exit with TASK_RUNNING make sure we enter with it,
> > + * otherwise we will destroy state.
> > + */
> > + if (WARN(current->state != TASK_RUNNING,
> > + "do not call blocking ops when !TASK_RUNNING; "
> > + "state=%lx set at [<%p>] %pS\n",
> > + current->state,
> > + (void *)current->task_state_change,
> > + (void *)current->task_state_change))
> > + __set_current_state(TASK_RUNNING);
>
> Question: now that we have ->task_state_change, perhaps it makes sense
> to redefine fixup_sleep()
>
> #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
> #define fixup_sleep() (current->task_state_change = 0)
> #else
> #define fixup_sleep() do { } while (0)
> #endif
>
> and make the WARN() above depend on task_state_change != 0 ?
>
> This is minor, but this way CONFIG_DEBUG_ATOMIC_SLEEP will not imply
> a subtle behavioural change.

You mean the __set_current_state() that's extra? I would actually argue
to keep that since it makes the 'problem' much worse.