[Bug nptl/12683] Race conditions in pthread cancellation

["carlos at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=12683

--- Comment #8 from Carlos O'Donell <carlos at redhat dot com> ---
(In reply to Rich Felker from comment #7)
> Glad to hear that. Have you taken a look at musl's cancellation
> implementation? The same mechanism could be used in glibc, or I think it
> could be modified somewhat to use DWARF2 CFI instead of the asm labels. The
> basic approach is that the cancellation signal handler examines the saved
> program counter register and determines whether it's in the critical range
> starting just before the pre-syscall check of the cancellation flag and the
> syscall instruction (based on asm labels for these two endpoints). The
> kernel then handles the atomicity of side effects for us: if the signal
> interrupts the syscall, the kernel must either complete what it's doing and
> return (positioning the program counter just past the address range that
> would allow cancellation to be acted upon), or reset the program counter to
> just before the syscall instruction and setup the register contents for
> restarting after the signal handler (in which case cancellation can be acted
> upon).

I have not looked at musl's cancellation implementation.

I assume you are parsing the rt_sigframe set down by the Linux kernel and
extracting information from that?

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