Re: BUG: ib_mad ftrace event unsupported migration

[Leonid Ravich]

> > > before starting throwing some patch into the the air  I would like to align with you the approach we should take here. 
> > > 
> > > my suggestion here : 
> > >- ftrace infra should verify no migration happen  (end and start happens on same CPU)  in case not we will  throw warning for the issue  .
> >
> >The scheduler should have. On entering the ring buffer code
> >ring_buffer_lock_reserver() it disables preemption and does not
> >re-enable it until ring_buffer_unlock_commit().
> >
> >The only way to migrate is if you re-enable preemption. WHICH IS A
> >BUG!

>So what on earth did that?

>I'm guessing some driver's query_pkey op, but AFAIK we don't have any
>explicit pre-emption reenablements in the code - unless it is sneaky..
trace infra uses preempt_disable_notrace/preempt_enable_notrace  to disable/enable preemtion but  my kernel compiled without CONFIG_PREEMPTION so this functions are only barriers - looks like the idea behind was to avoid involuntary preemtion  but in our case it is a voluntary (there is a wait_for_completion in the query_pkey  rabbit hole).

so no scheduler here to warn about illegal migration. 

>Leonid what driver are you testing?
mlx5 - (MLNX_OFED-5.3-1.0.0.1)