Re: [PATCH] mm/tlb: Fix use_mm() vs TLB invalidate

[Andy Lutomirski]

> On Feb 21, 2020, at 11:19 AM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> 
> ïOn Fri, Feb 21, 2020 at 3:11 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>> 
>> +       BUG_ON(!(tsk->flags & PF_KTHREAD));
>> +       BUG_ON(tsk->mm != NULL);
> 
> Stop this craziness.
> 
> There is absolutely ZERO excuse for this kind of garbage.
> 
> Making this a BUG_ON() will just cause all the possible debugging info
> to be thrown away and lost, and you often have a dead machine.
> 
> For absolutely no good reason.
> 
> Make it a WARN_ON_ONCE(). If it triggers, everything works the way it
> always did, but we get notified.
> 
> Stop with the stupid crazy BUG_ON() crap already. It is actively _bad_
> for debugging.
> 
>  

In this particular case, if we actually flub this, we are very likely to cause data corruption â weâre about to do user access with the wrong mm.

So I suppose we could switch to init_mm and carry on. *Something* will crash, but it probably wonât corrupt data or take down the machine.