nptl: Fix sem_wait and sem_timedwait cancellation (BZ#18243)

This patch fixes both sem_wait and sem_timedwait cancellation point for
uncontended case.  In this scenario only atomics are involved and thus
the futex cancellable call is not issue and a pending cancellation signal
is not handled.

The fix is straighforward by calling pthread_testcancel is both function
start.  Although it would be simpler to call CANCELLATION_P directly, I
decided to add an internal pthread_testcancel alias and use it to export
less internal implementation on such function.  A possible change on
how pthread_testcancel is internally implemented would lead to either
continue to force use CANCELLATION_P or to adjust its every use.

GLIBC testcase also does have tests for uncontended cases, test-cancel12
and test-cancel14.c,  however both are flawed by adding another
cancellation point just after thread pthread_cleanup_pop:

 47 static void *
 48 tf (void *arg)
 49 {
 50   pthread_cleanup_push (cleanup, NULL);
 51
 52   int e = pthread_barrier_wait (&bar);
 53   if (e != 0 && e != PTHREAD_BARRIER_SERIAL_THREAD)
 54     {
 55       puts ("tf: 1st barrier_wait failed");
 56       exit (1);
 57     }
 58
 59   /* This call should block and be cancelable.  */
 60   sem_wait (&sem);
 61
 62   pthread_cleanup_pop (0);
 63
 64   puts ("sem_wait returned");
 65
 66   return NULL;
 67 }

So sem_{timed}wait does not act on cancellation, pthread_cleanup_pop executes
'cleanup' and then 'puts' acts on cancellation.  Since pthread_cleanup_pop
removed the clean-up handler, it will ran only once and thus it won't accuse
an error to indicate sem_wait has not acted on the cancellation signal.

This patch also fixes this behavior by removing the cancellation point 'puts'.
It also adds some cleanup on all sem_{timed}wait cancel tests.

It partially fixes BZ #18243.  Checked on x86_64.

	[BZ #18243]
	* nptl/pthreadP.h (__pthread_testcancel): Add prototype and hidden_proto.
	* nptl/pthread_testcancel.c (pthread_cancel): Add internal aliais
	definition.
	* nptl/sem_timedwait.c (sem_timedwait): Add cancellation check for
	uncontended case.
	* nptl/sem_wait.c (__new_sem_wait): Likewise.
	* nptl/tst-cancel12.c (cleanup): Remove wrong cancellation point.
	(tf): Fix check for uncontended case.
	(do_test): Likewise.
	* nptl/tst-cancel13.c (cleanup): Remove wrong cancellation point.
	(tf): Fix check for uncontended case.
	(do_test): Likewise.
	* nptl/tst-cancel14.c (cleanup): Remove wrong cancellation point.
	(tf): Fix check for uncontended case.
	(do_test): Likewise.
	* nptl/tst-cancel15.c (cleanup): Remove wrong cancellation point.
	(tf): Fix check for uncontended case.
	(do_test): Likewise.

1 files changed, 13 insertions, 0 deletions

diff --git a/nptl/sem_wait.c b/nptl/sem_wait.c
index 84b523a768..b242c08d2e 100644
--- a/nptl/sem_wait.c
+++ b/nptl/sem_wait.c
@@ -23,6 +23,19 @@
 int
 __new_sem_wait (sem_t *sem)
 {
+  /* We need to check whether we need to act upon a cancellation request here
+     because POSIX specifies that cancellation points "shall occur" in
+     sem_wait and sem_timedwait, which also means that they need to check
+     this regardless whether they block or not (unlike "may occur"
+     functions).  See the POSIX Rationale for this requirement: Section
+     "Thread Cancellation Overview" [1] and austin group issue #1076 [2]
+     for thoughs on why this may be a suboptimal design.
+
+     [1] http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xsh_chap02.html
+     [2] http://austingroupbugs.net/view.php?id=1076 for thoughts on why this
+   */
+  __pthread_testcancel ();
+
   if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
     return 0;
   else