PING: V7 [PATCH] sysconf: Add _SC_MINSIGSTKSZ/_SC_SIGSTKSZ [BZ #20305]

[Florian Weimer]

* Zack Weinberg:

> I read this and I'm wondering how impractical it would be to invent a
> way to perform pthread_sigmask() operations without a system call.
> Abstractly, the signal mask for each thread _could_ be placed in user
> space at an ABI-specified location where the kernel can find it
> (bottom of the thread stack, maybe, or an offset from the TLS base);
> this doesn't make anything new possible (the kernel will just continue
> to ignore the bits for SIGKILL, SIGSEGV, etc.) so it wouldn't be a
> privilege violation.

Yes, this came up in the KTLS context.  The kernel also needs to set a
flag that indicates that unblocking requires a system call (so that a
pending signal can be delivered).  But it looks quite feasible to
implement.