Re: [PATCH] ptrace: restore smp_rmb() in __ptrace_may_access()

[Oleg Nesterov]

On 05/31, Peter Zijlstra wrote:
>
> 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,

Yes,

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

and it is still not clear to me if __ptrace_may_acess() has a control
dependency or not,

		if (uid_eq(caller_uid, tcred->euid) && ...)
			goto ok;
		retuurn;

	ok:
		// provide LOAD->LOAD
		smp_acquire__after_ctrl_dep();


again, again, I didn't suggest to change the patch, I was just curious
if it would be correct or not.

Oleg.