LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andy Lutomirski <luto@amacapital.net>
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 11:26:29 -0800
Message-ID: <CAHk-=whDHsbK3HTOpTF=ue_o04onRwTEaK_ZoJp_fjbqq4+=Jw@mail.gmail.com> (raw)
In-Reply-To: <6A09F721-0AD9-4B86-AB3E-563A1CF5ABDE@amacapital.net>

On Fri, Feb 21, 2020 at 11:22 AM Andy Lutomirski <luto@amacapital.net> wrote:
>
> 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?

IF this ever triggers, it has presumably been around for decades.

Nobody noticed.

Adding a WARN_ON_ONCE() means that somebody will now notice. Good.

Adding a BUG_ON() will now possibly mean that the machine is dead, and
is not sending the bug-report to anybody.

It's not going to hit, of course. But if you are 100% sure of that,
then it shouldn't exist at all.

And if you're not 100% sure of it, then it's going to be in some very
unusual circumstances (possibly some odd driver subsystem that does
something completely wrong - wouldn't be the first time), and the last
thing you want to do is lose the information about it.

So BUG_ON() is basically ALWAYS 100% the wrong thing to do. The
argument that "there could be memory corruption" is complete and utter
garbage. See above why.

Stop it. Seriously.

                Linus

  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
2020-02-21 19:26     ` Linus Torvalds [this message]
2020-02-21 23:10     ` Kees Cook
2020-02-21 23:57       ` Linus Torvalds
2020-02-22  0:29         ` Kees Cook

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAHk-=whDHsbK3HTOpTF=ue_o04onRwTEaK_ZoJp_fjbqq4+=Jw@mail.gmail.com' \
    --to=torvalds@linux-foundation.org \
    --cc=akpm@linux-foundation.org \
    --cc=axboe@kernel.dk \
    --cc=jannh@google.com \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@amacapital.net \
    --cc=peterz@infradead.org \
    --cc=will@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git