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Date: Sat, 12 Mar 2016 18:08:56 +0100
From: Ingo Molnar <>
To: Rich Felker <>,
	Linus Torvalds <>,
	Andy Lutomirski <>,
	the arch/x86 maintainers <>,
	Linux Kernel Mailing List <>,
	Borislav Petkov <>,
	"" <>,
	Andrew Morton <>,
	Thomas Gleixner <>,
	Peter Zijlstra <>,
	Szabolcs Nagy <>
Subject: Re: Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation

(Argh: Mail-Followup-To spam your mailer sets up is nasty!)

* Szabolcs Nagy <> wrote:

> >   4. A calls cancellation point and syscall correctly executes
> >   5. Once A enables cancellation again, the cancellation propagates.
> > 
> > So I still see no problem.
> i think the sticky signal design would work, but more
> complex than what we have and adds some atomic rmw ops
> into common code paths and not backward compatible.

Agreed about complexity, but note that the RMW ops shouldn't really be expensive 
here, as this should be a well-cached flag. Especially compared to:

> not using vsyscalls for cancellation-points sounds easier.

... FYI not using vsyscalls has _far_ higher cost than using well-cached RMW ops.

So ... what do you think about Linus's SA_SYNCHRONOUS approach? I think it can be 
made to work without much fuss.

There will still be different code paths on old and new kernels, but that's 



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