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:

quoted

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?

quoted

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.