nptl: Check if thread is already terminated in sigcancel_handler (BZ 32782)

The SIGCANCEL signal handler should not issue __syscall_do_cancel,
which calls __do_cancel and __pthread_unwind, if the cancellation
is already in proces (and libgcc unwind is not reentrant).  Any
cancellation signal received after is ignored.

Checked on x86_64-linux-gnu and aarch64-linux-gnu.

Tested-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Florian Weimer <fweimer@redhat.com>

benchtests/tanh-inputs

@@ -1,6 +1,7 @@
 ## args: double
 ## ret: double
 ## includes: math.h
+## name: workload-random
 -0x1.79ea722d33e33p-9
 -0x1.94d4e0c3df9bcp3
 -0x1.b63e91ff711e0p0

nptl/pthread_cancel.c

@@ -41,15 +41,17 @@ sigcancel_handler (int sig, siginfo_t *si, void *ctx)
       || si->si_code != SI_TKILL)
     return;
 
-  /* Check if asynchronous cancellation mode is set or if interrupted
+  /* Check if asynchronous cancellation mode is set and cancellation is not
-     instruction pointer falls within the cancellable syscall bridge.  For
+     already in progress, or if interrupted instruction pointer falls within
-     interruptable syscalls with external side-effects (i.e. partial reads),
+     the cancellable syscall bridge.
-     the kernel  will set the IP to after __syscall_cancel_arch_end, thus
+     For interruptable syscalls with external side-effects (i.e. partial
-     disabling the cancellation and allowing the process to handle such
+     reads), the kernel will set the IP to after __syscall_cancel_arch_end,
+     thus disabling the cancellation and allowing the process to handle such
      conditions.  */
   struct pthread *self = THREAD_SELF;
   int oldval = atomic_load_relaxed (&self->cancelhandling);
-  if (cancel_async_enabled (oldval) || cancellation_pc_check (ctx))
+  if (cancel_enabled_and_canceled_and_async (oldval)
+      || cancellation_pc_check (ctx))
     __syscall_do_cancel ();
 }
 

sysdeps/pthread/Makefile

@@ -106,6 +106,7 @@ tests += \
   tst-cancel28 \
   tst-cancel29 \
   tst-cancel30 \
+  tst-cancel32 \
   tst-cleanup0 \
   tst-cleanup1 \
   tst-cleanup2 \

sysdeps/pthread/tst-cancel32.c

@@ -0,0 +1,73 @@
+/* Check if pthread_setcanceltype disables asynchronous cancellation
+   once cancellation happens (BZ 32782)
+
+   Copyright (C) 2025 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
+   <https://www.gnu.org/licenses/>.  */
+
+/* The pthread_setcanceltype is a cancellation entrypoint, and if
+   asynchronous is enabled and the cancellation starts (on the second
+   pthread_setcanceltype call), the asynchronous should not restart
+   the process.  */
+
+#include <support/xthread.h>
+
+#define NITER     1000
+#define NTHREADS     8
+
+static void
+tf_cleanup (void *arg)
+{
+}
+
+static void *
+tf (void *closure)
+{
+  pthread_cleanup_push (tf_cleanup, NULL);
+  for (;;)
+    {
+      /* The only possible failure for pthread_setcanceltype is an
+	 invalid state type.  */
+      pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
+      pthread_setcanceltype (PTHREAD_CANCEL_DEFERRED, NULL);
+    }
+  pthread_cleanup_pop (1);
+
+  return NULL;
+}
+
+static void
+poll_threads (int nthreads)
+{
+  pthread_t thr[nthreads];
+  for (int i = 0; i < nthreads; i++)
+    thr[i] = xpthread_create (NULL, tf, NULL);
+  for (int i = 0; i < nthreads; i++)
+    xpthread_cancel (thr[i]);
+  for (int i = 0; i < nthreads; i++)
+    xpthread_join (thr[i]);
+}
+
+static int
+do_test (void)
+{
+  for (int k = 0; k < NITER; k++)
+    poll_threads (NTHREADS);
+
+  return 0;
+}
+
+#include <support/test-driver.c>