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Date: Mon, 1 Feb 2016 19:52:23 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Stas Sergeev <stsp@list.ru>
Cc: Linux kernel <linux-kernel@vger.kernel.org>, linux-api@vger.kernel.org,
        Andy Lutomirski <luto@amacapital.net>, Ingo Molnar <mingo@redhat.com>,
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Subject: Re: [PATCH 4/4] sigaltstack: allow disabling and re-enabling sas
 within sighandler
Message-ID: <20160201185223.GA21136@redhat.com>
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Stas, I probably missed something, but I don't understand your concerns,

On 02/01, Stas Sergeev wrote:
>
> 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.

Nothing? restore_sigaltstack() should work as expected?

> >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();

Yes, or

	sigaltstack({ DISABLE | FORCE}, &old_ss);
	swapcontext();
	sigaltstack(&old_ss, NULL);
	rt_sigreturn();

and if you are going to return from sighandler you do not even need the 2nd
sigaltstack(), you can rely on sigreturn.

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

Can't understand.... do you mean "set up new_sas" will be ignored because
rt_sigreturn() does restore_sigaltstack() ? I see no problem here...

Oleg.