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Message-ID: <20160312170856.GC1108@gmail.com> Date: Sat, 12 Mar 2016 18:08:56 +0100 From: Ingo Molnar <mingo@...nel.org> To: Rich Felker <dalias@...c.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>, the arch/x86 maintainers <x86@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...en8.de>, "musl@...ts.openwall.com" <musl@...ts.openwall.com>, Andrew Morton <akpm@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Szabolcs Nagy <nsz@...t70.net> Subject: Re: Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers (Argh: Mail-Followup-To spam your mailer sets up is nasty!) * Szabolcs Nagy <nsz@...t70.net> 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 unavoidable. Thanks, Ingo
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