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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Thomas Gleixner <tglx@linutronix.de>,
	Kees Cook <keescook@chromium.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>
Subject: Re: [GIT pull] sched/core for v5.16-rc1
Date: Mon, 1 Nov 2021 14:27:49 -0700	[thread overview]
Message-ID: <CAHk-=whwxyA11LQ+0y73nJAS4ZB=s8CeYM6OGCEzKiy+8fyLiw@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=whEbr+0ZSRMkQ1wqLCeBEiK7o2-Hm=55aTBpdeVxnFbVQ@mail.gmail.com>

On Mon, Nov 1, 2021 at 2:01 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Unwinders that need locks because they can do bad things if they are
> working on unstable data are EVIL and WRONG.

Note that this is fundamental: if you can fool an unwider to do
something bad just because the data isn't stable, then the unwinder is
truly horrendously buggy, and not usable.

It could be a user process doing bad things to the user stack frame
from another thread when profiling is enabled.

It could be debug code unwinding without locks for random reasons.

So I really don't like "take a lock for unwinding". It's a pretty bad
bug if the lock required.

I have to say, that commit message is pretty bad too. It doesn't
actually explain why this is needed. It just talks about the alleged
reasons why it should be stable, with no explanation of why that would
be an issue, and worth taking a core lock over.

The "Link" in the commit also is entirely useless, pointing back to
the emailed submission of the patch, rather than any useful discussion
about why the patch happened.

          Linus

  reply	other threads:[~2021-11-01 21:28 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-01  1:15 [GIT pull] irq/core for v5.16-rc1 Thomas Gleixner
2021-11-01  1:15 ` [GIT pull] locking/core " Thomas Gleixner
2021-11-01 21:20   ` pr-tracker-bot
2021-11-01  1:16 ` [GIT pull] objtool/core " Thomas Gleixner
2021-11-01 20:44   ` Linus Torvalds
2021-11-02  8:00     ` Peter Zijlstra
2021-11-02  8:06       ` Borislav Petkov
2021-11-02  9:05       ` Stackleak vs noinstr (Was: [GIT pull] objtool/core for v5.16-rc1) Peter Zijlstra
2021-11-02 10:03         ` Peter Zijlstra
2021-11-02 17:50           ` Linus Torvalds
2021-11-02 21:18             ` Borislav Petkov
2021-11-03  7:18           ` Alexander Popov
2021-11-03  8:19             ` Peter Zijlstra
2022-02-01 23:59           ` Kees Cook
2021-11-01 21:20   ` [GIT pull] objtool/core for v5.16-rc1 pr-tracker-bot
2021-11-01  1:16 ` [GIT pull] perf/core " Thomas Gleixner
2021-11-01 21:20   ` pr-tracker-bot
2021-11-01  1:16 ` [GIT pull] sched/core " Thomas Gleixner
2021-11-01 21:01   ` Linus Torvalds
2021-11-01 21:27     ` Linus Torvalds [this message]
2021-11-02  8:41       ` Peter Zijlstra
2021-11-03 13:52         ` Mark Rutland
2021-11-03 16:23         ` Linus Torvalds
2021-11-02  8:54     ` Peter Zijlstra
2021-11-01 21:20   ` pr-tracker-bot
2021-11-01  1:16 ` [GIT pull] timers/core " Thomas Gleixner
2021-11-01 21:20   ` pr-tracker-bot
2021-11-01  1:16 ` [GIT pull] x86/apic " Thomas Gleixner
2021-11-01 21:20   ` pr-tracker-bot
2021-11-01  1:52 ` [GIT pull RESEND] x86/fpu " Thomas Gleixner
2021-11-01 21:20   ` pr-tracker-bot
2021-11-01 21:19 ` [GIT pull] irq/core " pr-tracker-bot

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