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From: Andy Lutomirski <luto@amacapital.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Jens Axboe <axboe@kernel.dk>, Kees Cook <keescook@chromium.org>,
	Jann Horn <jannh@google.com>, Will Deacon <will@kernel.org>
Subject: Re: [PATCH] mm/tlb: Fix use_mm() vs TLB invalidate
Date: Fri, 21 Feb 2020 11:22:16 -0800
Message-ID: <6A09F721-0AD9-4B86-AB3E-563A1CF5ABDE@amacapital.net> (raw)
In-Reply-To: <CAHk-=wi4uO+Djqr4Jc1TnCofwxUTuXHtgkgwnVX86q06UGV6DA@mail.gmail.com>



> On Feb 21, 2020, at 11:19 AM, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> 
> On Fri, Feb 21, 2020 at 3:11 AM Peter Zijlstra <peterz@infradead.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.
> 
>  

In this particular case, if we actually flub this, we are very likely to cause data corruption — we’re 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 won’t corrupt data or take down the machine.

  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-21 11:11 Peter Zijlstra
2020-02-21 19:19 ` Linus Torvalds
2020-02-21 19:22   ` Andy Lutomirski [this message]
2020-02-21 19:26     ` Linus Torvalds
2020-02-21 23:10     ` Kees Cook
2020-02-21 23:57       ` Linus Torvalds
2020-02-22  0:29         ` Kees Cook

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