Re: [PATCH] sched: Use WARN_ON

[Arnd Bergmann]

On Thu, Jul 1, 2021 at 2:57 PM Christophe Leroy
<christophe.leroy@xxxxxxxxxx> wrote:
> Le 01/07/2021 à 14:50, Jason Wang a écrit :
> > The BUG_ON macro simplifies the if condition followed by BUG, but it
> > will lead to the kernel crashing. Therefore, we can try using WARN_ON
> > instead of if condition followed by BUG.
>
> But are you sure it is ok to continue if spu_acquire(ctx) returned false ?
> Shouldn't there be at least for fallback handling ?
>
> Something like:
>
>         if (WARN_ON(spu_acquire(ctx)))
>                 return;

I think you get a crash in either case:

- with the existing BUG_ON() there is an immediate backtrace and it stops there
- with WARN_ON() and continuing, you operate on a context that is not
  valid
- with the 'return', you get an endless loop, as it keeps calling
spusched_tick()
  without sleeping.

Out of those options, the existing BUG_ON() seems best.

       Arnd