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.

ChangeLog

@@ -1,5 +1,25 @@
 2016-09-15  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
+	[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.
+
 	* sysdeps/sparc/sparc32/sem_wait.c: Remove file.
 	* sysdeps/sparc/sparc32/sparcv9/sem_wait.c: Likewise.
 

nptl/pthreadP.h

@@ -491,6 +491,7 @@ extern int __pthread_setcanceltype (int type, int *oldtype);
 extern int __pthread_enable_asynccancel (void) attribute_hidden;
 extern void __pthread_disable_asynccancel (int oldtype)
      internal_function attribute_hidden;
+extern void __pthread_testcancel (void);
 
 #if IS_IN (libpthread)
 hidden_proto (__pthread_mutex_init)
@@ -505,6 +506,7 @@ hidden_proto (__pthread_getspecific)
 hidden_proto (__pthread_setspecific)
 hidden_proto (__pthread_once)
 hidden_proto (__pthread_setcancelstate)
+hidden_proto (__pthread_testcancel)
 #endif
 
 extern int __pthread_cond_broadcast_2_0 (pthread_cond_2_0_t *cond);

nptl/pthread_testcancel.c

@@ -21,7 +21,9 @@
 
 
 void
-pthread_testcancel (void)
+__pthread_testcancel (void)
 {
   CANCELLATION_P (THREAD_SELF);
 }
+strong_alias (__pthread_testcancel, pthread_testcancel)
+hidden_def (__pthread_testcancel)

nptl/sem_timedwait.c

@@ -30,6 +30,9 @@ sem_timedwait (sem_t *sem, const struct timespec *abstime)
       return -1;
     }
 
+  /* Check sem_wait.c for a more detailed explanation why it is required.  */
+  __pthread_testcancel ();
+
   if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
     return 0;
   else

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

nptl/tst-cancel12.c

@@ -1,4 +1,5 @@
-/* Copyright (C) 2003-2016 Free Software Foundation, Inc.
+/* Test sem_wait cancellation for uncontended case.
+   Copyright (C) 2003-2016 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@redhat.com>, 2003.
 
@@ -39,8 +40,6 @@ cleanup (void *arg)
       puts ("second call to cleanup");
       exit (1);
     }
-
-  printf ("cleanup call #%d\n", ncall);
 }
 
 
@@ -52,17 +51,15 @@ tf (void *arg)
   int e = pthread_barrier_wait (&bar);
   if (e != 0 && e != PTHREAD_BARRIER_SERIAL_THREAD)
     {
-      puts ("tf: 1st barrier_wait failed");
+      puts ("error: tf: 1st barrier_wait failed");
       exit (1);
     }
 
-  /* This call should block and be cancelable.  */
+  /* This call should be cancelable.  */
   sem_wait (&sem);
 
   pthread_cleanup_pop (0);
 
-  puts ("sem_wait returned");
-
   return NULL;
 }
 
@@ -74,47 +71,47 @@ do_test (void)
 
   if (pthread_barrier_init (&bar, NULL, 2) != 0)
     {
-      puts ("barrier_init failed");
+      puts ("error: barrier_init failed");
       exit (1);
     }
 
+  /* A value higher than 0 will check for uncontended pthread cancellation,
+     where the sem_wait operation will return immediatelly.  */
   if (sem_init (&sem, 0, 1) != 0)
     {
-      puts ("sem_init failed");
+      puts ("error: sem_init failed");
       exit (1);
     }
 
   if (pthread_create (&th, NULL, tf, NULL) != 0)
     {
-      puts ("create failed");
+      puts ("error: create failed");
       exit (1);
     }
 
-  /* Check whether cancellation is honored even before sem_wait does
-     anything.  */
   if (pthread_cancel (th) != 0)
     {
-      puts ("1st cancel failed");
+      puts ("error: pthread_cancel failed");
       exit (1);
     }
 
   int e = pthread_barrier_wait (&bar);
   if (e != 0 && e != PTHREAD_BARRIER_SERIAL_THREAD)
     {
-      puts ("1st barrier_wait failed");
+      puts ("error: 1st barrier_wait failed");
       exit (1);
     }
 
   void *r;
   if (pthread_join (th, &r) != 0)
     {
-      puts ("join failed");
+      puts ("error: pthread_join failed");
       exit (1);
     }
 
   if (r != PTHREAD_CANCELED)
     {
-      puts ("thread not canceled");
+      puts ("error: thread not canceled");
       exit (1);
     }
 

nptl/tst-cancel13.c

@@ -1,4 +1,5 @@
-/* Copyright (C) 2003-2016 Free Software Foundation, Inc.
+/* Test sem_wait cancellation for contended case.
+   Copyright (C) 2003-2016 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@redhat.com>, 2003.
 
@@ -39,8 +40,6 @@ cleanup (void *arg)
       puts ("second call to cleanup");
       exit (1);
     }
-
-  printf ("cleanup call #%d\n", ncall);
 }
 
 
@@ -52,7 +51,7 @@ tf (void *arg)
   int e = pthread_barrier_wait (&bar);
   if (e != 0 && e != PTHREAD_BARRIER_SERIAL_THREAD)
     {
-      puts ("tf: 1st barrier_wait failed");
+      puts ("error: tf: 1st barrier_wait failed");
       exit (1);
     }
 
@@ -61,8 +60,6 @@ tf (void *arg)
 
   pthread_cleanup_pop (0);
 
-  puts ("sem_wait returned");
-
   return NULL;
 }
 
@@ -74,26 +71,28 @@ do_test (void)
 
   if (pthread_barrier_init (&bar, NULL, 2) != 0)
     {
-      puts ("barrier_init failed");
+      puts ("error: barrier_init failed");
       exit (1);
     }
 
+  /* A value equal to 0 will check for contended pthread cancellation,
+     where the sem_wait operation will block.  */
   if (sem_init (&sem, 0, 0) != 0)
     {
-      puts ("sem_init failed");
+      puts ("error: sem_init failed");
       exit (1);
     }
 
   if (pthread_create (&th, NULL, tf, NULL) != 0)
     {
-      puts ("create failed");
+      puts ("error: create failed");
       exit (1);
     }
 
   int e = pthread_barrier_wait (&bar);
   if (e != 0 && e != PTHREAD_BARRIER_SERIAL_THREAD)
     {
-      puts ("1st barrier_wait failed");
+      puts ("error: 1st barrier_wait failed");
       exit (1);
     }
 
@@ -103,14 +102,14 @@ do_test (void)
   /* Check whether cancellation is honored when waiting in sem_wait.  */
   if (pthread_cancel (th) != 0)
     {
-      puts ("1st cancel failed");
+      puts ("error: 1st cancel failed");
       exit (1);
     }
 
   void *r;
   if (pthread_join (th, &r) != 0)
     {
-      puts ("join failed");
+      puts ("error: join failed");
       exit (1);
     }
 

nptl/tst-cancel14.c

@@ -1,4 +1,5 @@
-/* Copyright (C) 2003-2016 Free Software Foundation, Inc.
+/* Test sem_timedwait cancellation for uncontended case.
+   Copyright (C) 2003-2016 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@redhat.com>, 2003.
 
@@ -40,8 +41,6 @@ cleanup (void *arg)
       puts ("second call to cleanup");
       exit (1);
     }
-
-  printf ("cleanup call #%d\n", ncall);
 }
 
 
@@ -53,7 +52,7 @@ tf (void *arg)
   int e = pthread_barrier_wait (&bar);
   if (e != 0 && e != PTHREAD_BARRIER_SERIAL_THREAD)
     {
-      puts ("tf: 1st barrier_wait failed");
+      puts ("error: tf: 1st barrier_wait failed");
       exit (1);
     }
 
@@ -71,8 +70,6 @@ tf (void *arg)
 
   pthread_cleanup_pop (0);
 
-  puts ("sem_timedwait returned");
-
   return NULL;
 }
 
@@ -84,19 +81,19 @@ do_test (void)
 
   if (pthread_barrier_init (&bar, NULL, 2) != 0)
     {
-      puts ("barrier_init failed");
+      puts ("error: barrier_init failed");
       exit (1);
     }
 
   if (sem_init (&sem, 0, 1) != 0)
     {
-      puts ("sem_init failed");
+      puts ("error: sem_init failed");
       exit (1);
     }
 
   if (pthread_create (&th, NULL, tf, NULL) != 0)
     {
-      puts ("create failed");
+      puts ("error: create failed");
       exit (1);
     }
 
@@ -104,7 +101,7 @@ do_test (void)
      anything.  */
   if (pthread_cancel (th) != 0)
     {
-      puts ("1st cancel failed");
+      puts ("error: 1st cancel failed");
       exit (1);
     }
 

nptl/tst-cancel15.c

@@ -1,4 +1,5 @@
-/* Copyright (C) 2003-2016 Free Software Foundation, Inc.
+/* Test sem_timedwait cancellation for contended case.
+   Copyright (C) 2003-2016 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@redhat.com>, 2003.
 
@@ -40,8 +41,6 @@ cleanup (void *arg)
       puts ("second call to cleanup");
       exit (1);
     }
-
-  printf ("cleanup call #%d\n", ncall);
 }
 
 
@@ -55,7 +54,7 @@ tf (void *arg)
   e = pthread_barrier_wait (&bar);
   if (e != 0 && e != PTHREAD_BARRIER_SERIAL_THREAD)
     {
-      puts ("tf: 1st barrier_wait failed");
+      puts ("error: tf: 1st barrier_wait failed");
       exit (1);
     }
 
@@ -74,8 +73,6 @@ tf (void *arg)
 
   pthread_cleanup_pop (0);
 
-  printf ("sem_timedwait returned, e = %d, errno = %d\n", e, errno);
-
   return NULL;
 }
 
@@ -87,26 +84,26 @@ do_test (void)
 
   if (pthread_barrier_init (&bar, NULL, 2) != 0)
     {
-      puts ("barrier_init failed");
+      puts ("error: barrier_init failed");
       exit (1);
     }
 
   if (sem_init (&sem, 0, 0) != 0)
     {
-      puts ("sem_init failed");
+      puts ("error: sem_init failed");
       exit (1);
     }
 
   if (pthread_create (&th, NULL, tf, NULL) != 0)
     {
-      puts ("create failed");
+      puts ("error: create failed");
       exit (1);
     }
 
   int e = pthread_barrier_wait (&bar);
   if (e != 0 && e != PTHREAD_BARRIER_SERIAL_THREAD)
     {
-      puts ("1st barrier_wait failed");
+      puts ("error: 1st barrier_wait failed");
       exit (1);
     }
 
@@ -116,20 +113,20 @@ do_test (void)
   /* Check whether cancellation is honored when waiting in sem_timedwait.  */
   if (pthread_cancel (th) != 0)
     {
-      puts ("1st cancel failed");
+      puts ("error: 1st cancel failed");
       exit (1);
     }
 
   void *r;
   if (pthread_join (th, &r) != 0)
     {
-      puts ("join failed");
+      puts ("error: join failed");
       exit (1);
     }
 
   if (r != PTHREAD_CANCELED)
     {
-      puts ("thread not canceled");
+      puts ("error: thread not canceled");
       exit (1);
     }