linux-kernel - Re: [PATCH 4/4] sigaltstack: allow disabling and re-enabling sas within sighandler

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Date:	Mon, 1 Feb 2016 21:16:02 +0300
From:	Stas Sergeev <stsp@...t.ru>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Linux kernel <linux-kernel@...r.kernel.org>,
	linux-api@...r.kernel.org, Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Amanieu d'Antras <amanieu@...il.com>,
	Richard Weinberger <richard@....at>, Tejun Heo <tj@...nel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Jason Low <jason.low2@...com>,
	Heinrich Schuchardt <xypron.glpk@....de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Josh Triplett <josh@...htriplett.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Aleksa Sarai <cyphar@...har.com>,
	Paul Moore <pmoore@...hat.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Vladimir Davydov <vdavydov@...allels.com>
Subject: Re: [PATCH 4/4] sigaltstack: allow disabling and re-enabling sas
 within sighandler

01.02.2016 21:04, Oleg Nesterov пишет:
 > Yes, and SS_FORCE means "I know what I do", looks very simple.
But to me its not because I don't know what to do with
uc_stack after SS_FORCE is applied.

> I won't argue, but to me it would be better to keep this EPERM if !force.
> Just because we should avoid the incompatible changes if possible.
Ok then. Lets implement SS_FORCE.
What semantic should it have wrt uc_stack?

sigaltstack(SS_DISABLE | SS_FORCE);
swapcontext();
sigaltstack(set up new_sas);
rt_sigreturn();

What's at the end? Do we want a surprise for the user
that he's new_sas got ignored?