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/* Copyright (C) 2002-2024 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/>. */
#include <errno.h>
#include <signal.h>
#include <stdlib.h>
#include "pthreadP.h"
#include <atomic.h>
#include <sysdep.h>
#include <unistd.h>
#include <unwind-link.h>
#include <cancellation-pc-check.h>
#include <stdio.h>
#include <gnu/lib-names.h>
#include <sys/single_threaded.h>
/* For asynchronous cancellation we use a signal. */
static void
sigcancel_handler (int sig, siginfo_t *si, void *ctx)
{
/* Safety check. It would be possible to call this function for
other signals and send a signal from another process. This is not
correct and might even be a security problem. Try to catch as
many incorrect invocations as possible. */
if (sig != SIGCANCEL
|| si->si_pid != __getpid()
|| si->si_code != SI_TKILL)
return;
/* Check if asynchronous cancellation mode is set or if interrupted
instruction pointer falls within the cancellable syscall bridge. For
interruptable syscalls with external side-effects (i.e. partial 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))
__syscall_do_cancel ();
}
int
__pthread_cancel (pthread_t th)
{
volatile struct pthread *pd = (volatile struct pthread *) th;
if (pd->tid == 0)
/* The thread has already exited on the kernel side. Its outcome
(regular exit, other cancelation) has already been
determined. */
return 0;
static int init_sigcancel = 0;
if (atomic_load_relaxed (&init_sigcancel) == 0)
{
struct sigaction sa;
sa.sa_sigaction = sigcancel_handler;
/* The signal handle should be non-interruptible to avoid the risk of
spurious EINTR caused by SIGCANCEL sent to process or if
pthread_cancel() is called while cancellation is disabled in the
target thread. */
sa.sa_flags = SA_SIGINFO | SA_RESTART;
__sigemptyset (&sa.sa_mask);
__libc_sigaction (SIGCANCEL, &sa, NULL);
atomic_store_relaxed (&init_sigcancel, 1);
}
#ifdef SHARED
/* Trigger an error if libgcc_s cannot be loaded. */
{
struct unwind_link *unwind_link = __libc_unwind_link_get ();
if (unwind_link == NULL)
__libc_fatal (LIBGCC_S_SO
" must be installed for pthread_cancel to work\n");
}
#endif
/* Some syscalls are never restarted after being interrupted by a signal
handler, regardless of the use of SA_RESTART (they always fail with
EINTR). So pthread_cancel cannot send SIGCANCEL unless the cancellation
is enabled.
In this case the target thread is set as 'cancelled' (CANCELED_BITMASK)
by atomically setting 'cancelhandling' and the cancelation will be acted
upon on next cancellation entrypoing in the target thread.
It also requires to atomically check if cancellation is enabled, so the
state are also tracked on 'cancelhandling'. */
int result = 0;
int oldval = atomic_load_relaxed (&pd->cancelhandling);
int newval;
do
{
again:
newval = oldval | CANCELED_BITMASK;
if (oldval == newval)
break;
/* Only send the SIGANCEL signal if cancellation is enabled, since some
syscalls are never restarted even with SA_RESTART. The signal
will act iff async cancellation is enabled. */
if (cancel_enabled (newval))
{
if (!atomic_compare_exchange_weak_acquire (&pd->cancelhandling,
&oldval, newval))
goto again;
if (pd == THREAD_SELF)
/* This is not merely an optimization: An application may
call pthread_cancel (pthread_self ()) without calling
pthread_create, so the signal handler may not have been
set up for a self-cancel. */
{
if (cancel_async_enabled (newval))
__do_cancel (PTHREAD_CANCELED);
}
else
/* The cancellation handler will take care of marking the
thread as canceled. */
result = __pthread_kill_internal (th, SIGCANCEL);
break;
}
}
while (!atomic_compare_exchange_weak_acquire (&pd->cancelhandling, &oldval,
newval));
/* 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
__libc_single_threaded_internal = 0;
#endif
return result;
}
versioned_symbol (libc, __pthread_cancel, pthread_cancel, GLIBC_2_34);
#if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_34)
compat_symbol (libpthread, __pthread_cancel, pthread_cancel, GLIBC_2_0);
#endif
/* Ensure that the unwinder is always linked in (the __pthread_unwind
reference from __do_cancel is weak). Use ___pthread_unwind_next
(three underscores) to produce a strong reference to the same
file. */
PTHREAD_STATIC_FN_REQUIRE (___pthread_unwind_next)
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