[PATCH] Fix missing wake-ups in pthread_rwlock_rdlock.

[Torvald Riegel]

This adds wake-ups that would be missing if assuming that for a
non-writer-preferring rwlock, if one thread has acquired a rdlock and
does not release it, another thread will eventually acquire a rdlock too
despite concurrent write lock acquisition attempts.  BZ 14958 is about
supporting this assumption.

I've commented on the BZ why I think that strictly speaking, this isn't
a valid test case, but nonetheless worth supporting:
https://sourceware.org/bugzilla/show_bug.cgi?id=14958#c7

I have no intention to work on supporting the requirements about Thread
Execution Scheduling and priorities for pthread_rwlock_rdlock (see BZ
13701); we claim to support it, so with this patch, we can claim that we
assume assume the priorities to all be equal (in which case readers are
to be preferred).  See
http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_rwlock_rdlock.html

Tested on x86_64-linux. (Applies on top of the other rwlock fix I sent.)
OK?

2015-04-28  Torvald Riegel  <triegel@redhat.com>

	[BZ #14958]
	* nptl/pthread_rwlock_rdlock.c (__pthread_rwlock_rdlock): Add missing
	wake-up.
	(__pthread_rwlock_rdlock_slow): Likewise.
	* nptl/pthread_rwlock_timedrdlock.c (pthread_rwlock_timedrdlock):
	Likewise.
	* nptl/pthread_rwlock_tryrdlock.c (__pthread_rwlock_tryrdlock):
	Likewise.
	* nptl/pthread_rwlock_unlock.c (__pthread_rwlock_unlock): Add comments.
	* nptl/tst-rwlock16.c: New file.
	* nptl/Makefile (tests): Add new test.
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