tree 5d0ffa57b7a59fdc6323afd105fcdf748f636776
parent dbcfb16e43af28ba919f651c51d7a2f15af656a1
author Rich Felker <dalias@aerifal.cx> 1537033541 -0400
committer Rich Felker <dalias@aerifal.cx> 1537035726 -0400

check for kernel support before allowing robust mutex creation

on some archs, linux support for futex operations (including
robust_list processing) that depend on kernelspace CAS is conditional
on a runtime check. as of linux 4.18, this check fails unconditionally
on nommu archs that perform it, and spurious failure on powerpc64 was
observed but not explained. it's also possible that futex support is
omitted entirely, or that the kernel is older than 2.6.17. for most
futex ops, ENOSYS does not yield hard breakage; userspace will just
spin at 100% cpu load. but for robust mutexes, correct behavior
depends on the kernel functionality.

use the get_robust_list syscall to probe for support at the first call
to pthread_mutexattr_setrobust, and block creation of robust mutexes
with a reportable error if they can't be supported.