Allow a single-threaded program to cancel itself

There is nothing in the POSIX specification to disallow a
single-threaded program from cancelling itself, so we forcibly enable
multiple_threads to allow the next available cancellation point in the
thread to run.

Also added additional tests to cover various cancellation scenarios.

12 files changed, 290 insertions, 2 deletions

diff --git a/nptl/ChangeLog b/nptl/ChangeLog
index cfc679cbe8..bd7311fb09 100644
--- a/nptl/ChangeLog
+++ b/nptl/ChangeLog
@@ -1,3 +1,22 @@
+2012-05-15  Siddhesh Poyarekar  <siddhesh@redhat.com>
+	    Jakub Jelinek  <jakub@redhat.com>
+
+	[BZ #13613]
+	* Makefile (tests): Add test cases.
+	* descr.h (struct pthread): Add a comment describing multiple_threads.
+	* pthreadP.h (__pthread_multiple_threads): Expand comment to include
+	single-process case.
+	* pthread_cancel.c (pthread_cancel): Enable multiple_threads
+	before setting cancelstate of the thread.
+	* sysdeps/unix/sysv/linux/libc_multiple_threads.c
+	(__libc_multiple_threads): Add explanatory comment.
+	* tst-cancel-self-cancelstate.c: New test case.
+	* tst-cancel-self-canceltype.c: Likewise.
+	* tst-cancel-self-cleanup.c: Supporting file for test cases.
+	* tst-cancel-self-testcancel.c: New test case.
+	* tst-cancel-self.c: Likewise.
+	* vars.c: Expand comment to include single-process case.
+
 2012-05-14  H.J. Lu  <hongjiu.lu@intel.com>
 
 	* sysdeps/x86_64/tls.h: Don't include <bits/wordsize.h>.
diff --git a/nptl/Makefile b/nptl/Makefile
index 07a10225f1..2a36d01720 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -236,6 +236,8 @@ tests = tst-typesizes \
 	tst-cancel11 tst-cancel12 tst-cancel13 tst-cancel14 tst-cancel15 \
 	tst-cancel16 tst-cancel17 tst-cancel18 tst-cancel19 tst-cancel20 \
 	tst-cancel21 tst-cancel22 tst-cancel23 tst-cancel24 tst-cancel25 \
+	tst-cancel-self tst-cancel-self-cancelstate \
+	tst-cancel-self-canceltype tst-cancel-self-testcancel \
 	tst-cleanup0 tst-cleanup1 tst-cleanup2 tst-cleanup3 tst-cleanup4 \
 	tst-flock1 tst-flock2 \
 	tst-signal1 tst-signal2 tst-signal3 tst-signal4 tst-signal5 \
diff --git a/nptl/descr.h b/nptl/descr.h
index c2fabeb1a0..60d2d22e7a 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -131,6 +131,21 @@ struct pthread
 #else
     struct
     {
+      /* multiple_threads is enabled either when the process has spawned at
+	 least one thread or when a single-threaded process cancels itself.
+	 This enables additional code to introduce locking before doing some
+	 compare_and_exchange operations and also enable cancellation points.
+	 The concepts of multiple threads and cancellation points ideally
+	 should be separate, since it is not necessary for multiple threads to
+	 have been created for cancellation points to be enabled, as is the
+	 case is when single-threaded process cancels itself.
+
+	 Since enabling multiple_threads enables additional code in
+	 cancellation points and compare_and_exchange operations, there is a
+	 potential for an unneeded performance hit when it is enabled in a
+	 single-threaded, self-canceling process.  This is OK though, since a
+	 single-threaded process will enable async cancellation only when it
+	 looks to cancel itself and is hence going to end anyway.  */
       int multiple_threads;
       int gscope_flag;
 # ifndef __ASSUME_PRIVATE_FUTEX
diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index 68c690e88e..24a24717fc 100644
--- a/nptl/pthreadP.h
+++ b/nptl/pthreadP.h
@@ -378,7 +378,9 @@ extern int *__libc_pthread_init (unsigned long int *ptr,
 				 const struct pthread_functions *functions)
      internal_function;
 
-/* Variable set to a nonzero value if more than one thread runs or ran.  */
+/* Variable set to a nonzero value either if more than one thread runs or ran,
+   or if a single-threaded process is trying to cancel itself.  See
+   nptl/descr.h for more context on the single-threaded process case.  */
 extern int __pthread_multiple_threads attribute_hidden;
 /* Pointer to the corresponding variable in libc.  */
 extern int *__libc_multiple_threads_ptr attribute_hidden;
diff --git a/nptl/pthread_cancel.c b/nptl/pthread_cancel.c
index 249aa1109a..1bfca63581 100644
--- a/nptl/pthread_cancel.c
+++ b/nptl/pthread_cancel.c
@@ -95,6 +95,14 @@ pthread_cancel (th)
 
 	  break;
 	}
+
+	/* A single-threaded process should be able to kill itself, since there is
+	   nothing in the POSIX specification that says that it cannot.  So we set
+	   multiple_threads to true so that cancellation points get executed.  */
+	THREAD_SETMEM (THREAD_SELF, header.multiple_threads, 1);
+#ifndef TLS_MULTIPLE_THREADS_IN_TCB
+	__pthread_multiple_threads = *__libc_multiple_threads_ptr = 1;
+#endif
     }
   /* Mark the thread as canceled.  This has to be done
      atomically since other bits could be modified as well.  */
diff --git a/nptl/sysdeps/unix/sysv/linux/libc_multiple_threads.c b/nptl/sysdeps/unix/sysv/linux/libc_multiple_threads.c
index 7fffb0d808..459b8cf7c0 100644
--- a/nptl/sysdeps/unix/sysv/linux/libc_multiple_threads.c
+++ b/nptl/sysdeps/unix/sysv/linux/libc_multiple_threads.c
@@ -20,6 +20,9 @@
 
 #ifndef NOT_IN_libc
 # ifndef TLS_MULTIPLE_THREADS_IN_TCB
+/* Variable set to a nonzero value either if more than one thread runs or ran,
+   or if a single-threaded process is trying to cancel itself.  See
+   nptl/descr.h for more context on the single-threaded process case.  */
 int __libc_multiple_threads attribute_hidden;
 # endif
 #endif
diff --git a/nptl/tst-cancel-self-cancelstate.c b/nptl/tst-cancel-self-cancelstate.c
new file mode 100644
index 0000000000..c82e6f3ced
--- /dev/null
+++ b/nptl/tst-cancel-self-cancelstate.c
@@ -0,0 +1,65 @@
+/* Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include "tst-cancel-self-cleanup.c"
+
+
+static int
+do_test (void)
+{
+  int ret = 0;
+  volatile int should_fail = 1;
+
+  pthread_cleanup_push (cleanup, &should_fail);
+
+  if ((ret = pthread_setcancelstate (PTHREAD_CANCEL_DISABLE, NULL)) != 0)
+    {
+      printf ("setcancelstate(disable) failed: %s\n", strerror (ret));
+      exit (1);
+    }
+
+  if ((ret = pthread_cancel (pthread_self ())) != 0)
+    {
+      printf ("cancel failed: %s\n", strerror (ret));
+      exit (1);
+    }
+
+  usleep (100);
+  should_fail = 0;
+
+  if ((ret = pthread_setcancelstate (PTHREAD_CANCEL_ENABLE, NULL)) != 0)
+    {
+      printf ("setcancelstate(enable) failed: %s\n", strerror (ret));
+      exit (1);
+    }
+
+  /* The write syscall within this printf should give us our cancellation
+     point.  */
+  printf ("Could not cancel self.\n");
+  pthread_cleanup_pop (0);
+
+  return 1;
+}
+
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/nptl/tst-cancel-self-canceltype.c b/nptl/tst-cancel-self-canceltype.c
new file mode 100644
index 0000000000..c9bb653131
--- /dev/null
+++ b/nptl/tst-cancel-self-canceltype.c
@@ -0,0 +1,53 @@
+/* Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include "tst-cancel-self-cleanup.c"
+
+
+static int
+do_test (void)
+{
+  int ret = 0, should_fail = 0;
+
+  pthread_cleanup_push (cleanup, &should_fail);
+
+  if ((ret = pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, NULL)) != 0)
+    {
+      printf ("setcanceltype failed: %s\n", strerror (ret));
+      exit (1);
+    }
+
+  if ((ret = pthread_cancel (pthread_self ())) != 0)
+    {
+      printf ("cancel failed: %s\n", strerror (ret));
+      exit (1);
+    }
+
+  /* Wait to be canceled. Don't give any cancellation points to play with.  */
+  while (1);
+  pthread_cleanup_pop (0);
+
+  return 1;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/nptl/tst-cancel-self-cleanup.c b/nptl/tst-cancel-self-cleanup.c
new file mode 100644
index 0000000000..9b15f555dc
--- /dev/null
+++ b/nptl/tst-cancel-self-cleanup.c
@@ -0,0 +1,23 @@
+/* Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+static void
+cleanup (void *cleanup_should_fail)
+{
+  printf ("Main thread got cancelled and is being cleaned up now\n");
+  exit (*(int *)cleanup_should_fail);
+}
diff --git a/nptl/tst-cancel-self-testcancel.c b/nptl/tst-cancel-self-testcancel.c
new file mode 100644
index 0000000000..c9422321ce
--- /dev/null
+++ b/nptl/tst-cancel-self-testcancel.c
@@ -0,0 +1,48 @@
+/* Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include "tst-cancel-self-cleanup.c"
+
+
+static int
+do_test (void)
+{
+  int ret = 0, should_fail = 0;
+
+  pthread_cleanup_push (cleanup, &should_fail);
+  if ((ret = pthread_cancel (pthread_self ())) != 0)
+    {
+      printf ("cancel failed: %s\n", strerror (ret));
+      exit (1);
+    }
+
+  pthread_testcancel ();
+
+  printf ("Could not cancel self.\n");
+  pthread_cleanup_pop (0);
+
+  return 1;
+}
+
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/nptl/tst-cancel-self.c b/nptl/tst-cancel-self.c
new file mode 100644
index 0000000000..966698ca3b
--- /dev/null
+++ b/nptl/tst-cancel-self.c
@@ -0,0 +1,48 @@
+/* Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include "tst-cancel-self-cleanup.c"
+
+
+static int
+do_test (void)
+{
+  int ret = 0, should_fail = 0;
+
+  pthread_cleanup_push (cleanup, &should_fail);
+  if ((ret = pthread_cancel (pthread_self ())) != 0)
+    {
+      printf ("cancel failed: %s\n", strerror (ret));
+      exit (1);
+    }
+
+  /* The write syscall within this printf should give us our cancellation
+     point.  */
+  printf ("Could not cancel self.\n");
+  pthread_cleanup_pop (0);
+
+  return 1;
+}
+
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/nptl/vars.c b/nptl/vars.c
index 8f3023cfc0..43a6e3957c 100644
--- a/nptl/vars.c
+++ b/nptl/vars.c
@@ -32,7 +32,9 @@ size_t __default_stacksize attribute_hidden
 int __is_smp attribute_hidden;
 
 #ifndef TLS_MULTIPLE_THREADS_IN_TCB
-/* Variable set to a nonzero value if more than one thread runs or ran.  */
+/* Variable set to a nonzero value either if more than one thread runs or ran,
+   or if a single-threaded process is trying to cancel itself.  See
+   nptl/descr.h for more context on the single-threaded process case.  */
 int __pthread_multiple_threads attribute_hidden;
 #endif