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From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Jann Horn <jannh@google.com>,
	"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: Fri, 31 May 2019 11:12:45 +0200	[thread overview]
Message-ID: <20190531091245.GN2677@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190530120531.GE22536@redhat.com>

On Thu, May 30, 2019 at 02:05:31PM +0200, Oleg Nesterov wrote:
> > 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.

So it hard relies on being part of a control dependency, note how the
comment says that architectures that do not do load speculation can
override the smp_rmb() default with barrier() (and we used have an
architecture that made use of that, although it's been since removed).

IOW, it is an error to use smp_acquire__after_ctrl_dep() without an
(immediate) preceding branch.

  reply	other threads:[~2019-05-31  9:12 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-29 11:31 [PATCH] ptrace: restore smp_rmb() in __ptrace_may_access() 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
2019-05-31  9:12       ` Peter Zijlstra [this message]
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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