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

Oleg Nesterov
2014-10-02T21:37:55Z

On 10/02, Peter Zijlstra wrote:
>
> On Wed, Oct 01, 2014 at 08:35:49PM +0200, Oleg Nesterov wrote:
> >
> > For example, let's suppose that we do not have 01/11 which fixes
> > mutex_lock(). Then this code
> >
> > set_current_state(TASK_UNINTERRUPTIBLE);
> > ...
> > fixup_sleep();
> > ...
> > mutex_lock(some_mutex);
> >
> > can hang, but only if !CONFIG_DEBUG_ATOMIC_SLEEP.
>
> Right, but we should not use fixup_sleep() in this case,

(well, I am not really sure but this is off-topic and I agree this needs
another discussion)

> because its an
> actual proper bug, we should fix it, not paper over it.

Exactly! this is what I meant: CONFIG_DEBUG_ATOMIC_SLEEP will hide the
bug we need to fix.

> > So perhaps it makes sense to redefine it
> >
> > #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
> > #define fixup_sleep() (current->task_state_change = 0)
> > #else
> > #define fixup_sleep() do { } while (0)
> > #endif
> >
> > and change __might_sleep()
> >
> > - if (WARN(current->state != TASK_RUNNING,
> > + if (WARN(current->state != TASK_RUNNING && current->task_state_change != 0,
> >
> > ?
>
> So I'm hesitant to go that way because it adds extra state dependency.

OK. We can always reconsider this later. I spammed you only because I
wanted to understand what did me/you/both missed in this discussion.

> What if someone 'forgets' to use the *set*state() helpers.

Yes, this is true. Although we want to fix them anyway, if nothing else
for this warning in might_sleep().

Oleg.