losing events with EPOLLONESHOT and cancellation

[Eric Wong <normalperson at yhbt dot net>]

I seem to be encountering lost events with epoll_wait/epoll_pwait when
using EPOLLONESHOT and pthreads cancellation.

Based on my reading of sysdeps/unix/sysv/linux/epoll_pwait.c; if the
result of epoll_pwait is greater than 0 (events are available), it is
still possible for LIBC_CANCEL_RESET to cancel the thread and cause
result to never be returned (to other, uncancelled threads running
epoll_pwait).

Is my observation correct?

relevant code in sysdeps/unix/sysv/linux/epoll_pwait.c
---------------------------------8<--------------------------------
  int oldtype = LIBC_CANCEL_ASYNC ();

  int result = INLINE_SYSCALL (epoll_pwait, 6, epfd, events, maxevents,
			       timeout, set, _NSIG / 8);

  LIBC_CANCEL_RESET (oldtype);

  return result;
---------------------------------8<--------------------------------

Similarly, ports/sysdeps/unix/sysv/linux/generic/recv.c implements
identical logic for recv, so am I correct data could be lost (and not
readable by another, non-cancelled thread) if a recv caller is
cancelled when recv is successful?

Thanks in advance for any help.