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Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers

From Ingo Molnar <mingo@kernel.org>
Newsgroups linux.kernel
Subject Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers
Date 2016-03-12 18:10 +0100
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* Szabolcs Nagy <nsz@port70.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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Thread

[RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Andy Lutomirski <luto@kernel.org> - 2016-03-09 02:30 +0100
  Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Ingo Molnar <mingo@kernel.org> - 2016-03-09 10:00 +0100
    Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Szabolcs Nagy <nsz@port70.net> - 2016-03-09 12:40 +0100
      Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Szabolcs Nagy <nsz@port70.net> - 2016-03-09 12:50 +0100
      Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-09 20:50 +0100
        Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Andy Lutomirski <luto@amacapital.net> - 2016-03-09 22:00 +0100
          Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-09 22:30 +0100
          Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Ingo Molnar <mingo@kernel.org> - 2016-03-10 12:00 +0100
        Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Rich Felker <dalias@libc.org> - 2016-03-10 04:40 +0100
          Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Ingo Molnar <mingo@kernel.org> - 2016-03-10 12:20 +0100
            Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Rich Felker <dalias@libc.org> - 2016-03-10 17:50 +0100
              Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Ingo Molnar <mingo@kernel.org> - 2016-03-10 19:10 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Rich Felker <dalias@libc.org> - 2016-03-11 00:30 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Szabolcs Nagy <nsz@port70.net> - 2016-03-11 01:20 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Rich Felker <dalias@libc.org> - 2016-03-11 01:50 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Andy Lutomirski <luto@amacapital.net> - 2016-03-11 02:20 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Szabolcs Nagy <nsz@port70.net> - 2016-03-11 02:40 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Rich Felker <dalias@libc.org> - 2016-03-11 03:00 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Szabolcs Nagy <nsz@port70.net> - 2016-03-11 03:00 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Ingo Molnar <mingo@kernel.org> - 2016-03-11 10:40 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Szabolcs Nagy <nsz@port70.net> - 2016-03-11 12:40 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-11 20:30 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Andy Lutomirski <luto@amacapital.net> - 2016-03-11 20:40 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-11 20:40 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-11 20:50 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Ingo Molnar <mingo@kernel.org> - 2016-03-12 18:10 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Rich Felker <dalias@libc.org> - 2016-03-12 19:20 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Ingo Molnar <mingo@kernel.org> - 2016-03-12 18:10 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Rich Felker <dalias@libc.org> - 2016-03-12 19:10 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Ingo Molnar <mingo@kernel.org> - 2016-03-12 19:50 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Rich Felker <dalias@libc.org> - 2016-03-12 20:10 +0100
                Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation  helpers Ingo Molnar <mingo@kernel.org> - 2016-03-12 18:10 +0100
  Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Andy Lutomirski <luto@amacapital.net> - 2016-03-09 19:00 +0100
    Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Andy Lutomirski <luto@amacapital.net> - 2016-03-09 22:30 +0100
      Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Andy Lutomirski <luto@amacapital.net> - 2016-03-12 19:20 +0100

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