Re: [RT PATCH 3/3] hrtimer: Prevent using uninitialized spin_lock in hrtimer_grab_expiry_lock()

[Julien Grall]

Hi Thomas,

Thank you for the review.

On 21/08/2019 15:02, Thomas Gleixner wrote:
> On Wed, 21 Aug 2019, Julien Grall wrote:
>
> > migration_base is used as a placeholder when an hrtimer is switching
> > between base (see switch_hrtimer_timer_base). It is possible
> > theoritically possible to have timer->base equal to migration_base.
> >
> > Even if it is a placeholder, it would pass all the current check in
> > hrtimer_grab_expiry_lock() leading to use softirq_expiry_lock
> > uninitialized.
> >
> > This is can be prevented by checking whether the base is equal to
> > the placeholder (i.e. migration_base).
>
> That's a lame argument. The point is that it does not make sense to do that
> on migration base, but not for the reason you are giving (uninitialized
> lock).

Fair point, I will update the commit message.

> If base == migration_base then there is no point to lock soft_expiry_lock
> simply because the timer is not executing the callback in soft irq context
> and the whole lock/unlock dance can be avoided.
>
> But, yes. Good catch.

Do you want me to resend the series or can I just provide an update to the 
commit message here?

Cheers,

--
Julien Grall