linux-kernel - Re: [PATCH] mm/tlb: Fix use

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Message-ID: <CAHk-=wi4uO+Djqr4Jc1TnCofwxUTuXHtgkgwnVX86q06UGV6DA@mail.gmail.com>
Date:   Fri, 21 Feb 2020 11:19:22 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jens Axboe <axboe@...nel.dk>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH] mm/tlb: Fix use_mm() vs TLB invalidate

On Fri, Feb 21, 2020 at 3:11 AM Peter Zijlstra <peterz@...radead.org> 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.

              Linus