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From: Oleg Nesterov <oleg@redhat.com>
To: Jann Horn <jannh@google.com>
Cc: "Eric W . Biederman" <ebiederm@xmission.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Kees Cook <keescook@chromium.org>,
	David Howells <dhowells@redhat.com>,
	kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ptrace: restore smp_rmb() in __ptrace_may_access()
Date: Thu, 30 May 2019 14:05:31 +0200	[thread overview]
Message-ID: <20190530120531.GE22536@redhat.com> (raw)
In-Reply-To: <CAG48ez3S1c_cd8RNSb9TrF66d+1AMAxD4zh-kixQ6uSEnmS-tg@mail.gmail.com>

On 05/29, Jann Horn wrote:
>
> > (I am wondering if smp_acquire__after_ctrl_dep() could be used instead, just to
> >  make this code look more confusing)
>
> Uuh, I had no idea that that barrier type exists. The helper isn't
> even explicitly mentioned in Documentation/memory-barriers.rst. I
> don't really want to use dark magic in the middle of ptrace access
> logic...

Yes. and if it was not clear I didn't try to seriously suggest to use this
barrier. I was just curious if it can be used or not in this particular case.

> Anyway, looking at it, I think smp_acquire__after_ctrl_dep() doesn't
> make sense here;

Well I still _think_ it should work, it provides the LOAD-LOAD ordering
and this is what we need.

But I can be easily wrong, and again, I wasn't serious.

Oleg.


  parent reply	other threads:[~2019-05-30 12:05 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-29 11:31 Jann Horn
2019-05-29 15:59 ` Eric W. Biederman
2019-05-29 16:01   ` Jann Horn
2019-05-29 16:21 ` Oleg Nesterov
2019-05-29 17:38   ` Jann Horn
2019-05-30  1:41     ` Eric W. Biederman
2019-05-31 15:04       ` Jann Horn
2019-05-30 10:34     ` Andrea Parri
2019-05-31  9:08       ` Peter Zijlstra
2019-05-30 12:05     ` Oleg Nesterov [this message]
2019-05-31  9:12       ` Peter Zijlstra
2019-05-31  9:55         ` Oleg Nesterov
2019-05-29 21:02   ` Jann Horn
2019-05-29 18:55 ` Kees Cook
2019-05-30 12:34 ` Oleg Nesterov
2019-05-31 11:56   ` Jann Horn
2019-05-31 13:35     ` Oleg Nesterov
2019-05-31 19:37       ` Jann Horn

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