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

From Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups linux.kernel
Subject Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers
Date 2016-03-11 20:40 +0100
Message-ID <rbB4K-2v3-13@gated-at.bofh.it> (permalink)
References (8 earlier) <rbibN-5JJ-27@gated-at.bofh.it> <rbrI5-44N-3@gated-at.bofh.it> <rbtAe-5vz-3@gated-at.bofh.it> <rbAV4-2r7-19@gated-at.bofh.it> <rbB4K-2v3-9@gated-at.bofh.it>
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On Fri, Mar 11, 2016 at 11:30 AM, Andy Lutomirski <luto@amacapital.net> wrote:
>
> I think that this would almost work for musl, except that musl would
> still need to be able to tell whether the syscall that eventually gets
> interrupted is a cancellation point, which still may require some
> ability to unwind from the vdso.  The syscall handler can easily tell
> the syscall number (it's in EAX), but it may need the effective EIP as
> well.

So having tried to read the posix manual pages on this, it looks like
there is a list of *minimal* cancellation points, but that saying "any
system call is a cancellation point" is also perfectly valid.

 "An implementation may also mark other functions not specified in the
standard as cancellation  points"

Of course, musl may have more strict ideas than that on cancellation
points.  The "any system call" would make even trivial non-blocking
ones like "futex_wake()" and "getpid()" be cancellation points. So
maybe "any system call" isn't acceptable.

But if it *is* acceptable, that would be a pretty simple kernel mod, I think.

And I could see others possibly wanting to use synchronous signal
handlers. It's not like musl is the only project ever to have had
races with signals..

              Linus

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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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