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glibc/SOURCES/glibc-upstream-2.34-14.patch

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commit a8ac8c4725ddb1119764126a8674a04c9dd5aea8
Author: Florian Weimer <fweimer@redhat.com>
Date: Mon Sep 13 11:06:08 2021 +0200
nptl: Fix race between pthread_kill and thread exit (bug 12889)
A new thread exit lock and flag are introduced. They are used to
detect that the thread is about to exit or has exited in
__pthread_kill_internal, and the signal is not sent in this case.
The test sysdeps/pthread/tst-pthread_cancel-select-loop.c is derived
from a downstream test originally written by Marek Polacek.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
(cherry picked from commit 526c3cf11ee9367344b6b15d669e4c3cb461a2be)
diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index cfe37a3443b69454..50065bc9bd8a28e5 100644
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -32,6 +32,7 @@
#include <futex-internal.h>
#include <kernel-features.h>
#include <nptl-stack.h>
+#include <libc-lock.h>
/* Default alignment of stack. */
#ifndef STACK_ALIGN
@@ -127,6 +128,8 @@ get_cached_stack (size_t *sizep, void **memp)
/* No pending event. */
result->nextevent = NULL;
+ result->exiting = false;
+ __libc_lock_init (result->exit_lock);
result->tls_state = (struct tls_internal_t) { 0 };
/* Clear the DTV. */
diff --git a/nptl/descr.h b/nptl/descr.h
index c85778d44941a42f..4de84138fb960fa4 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -396,6 +396,12 @@ struct pthread
PTHREAD_CANCEL_ASYNCHRONOUS). */
unsigned char canceltype;
+ /* Used in __pthread_kill_internal to detected a thread that has
+ exited or is about to exit. exit_lock must only be acquired
+ after blocking signals. */
+ bool exiting;
+ int exit_lock; /* A low-level lock (for use with __libc_lock_init etc). */
+
/* Used on strsignal. */
struct tls_internal_t tls_state;
diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
index d8ec299cb1661e82..33b426fc682300dc 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -37,6 +37,7 @@
#include <sys/single_threaded.h>
#include <version.h>
#include <clone_internal.h>
+#include <futex-internal.h>
#include <shlib-compat.h>
@@ -485,6 +486,19 @@ start_thread (void *arg)
/* This was the last thread. */
exit (0);
+ /* This prevents sending a signal from this thread to itself during
+ its final stages. This must come after the exit call above
+ because atexit handlers must not run with signals blocked. */
+ __libc_signal_block_all (NULL);
+
+ /* Tell __pthread_kill_internal that this thread is about to exit.
+ If there is a __pthread_kill_internal in progress, this delays
+ the thread exit until the signal has been queued by the kernel
+ (so that the TID used to send it remains valid). */
+ __libc_lock_lock (pd->exit_lock);
+ pd->exiting = true;
+ __libc_lock_unlock (pd->exit_lock);
+
#ifndef __ASSUME_SET_ROBUST_LIST
/* If this thread has any robust mutexes locked, handle them now. */
# if __PTHREAD_MUTEX_HAVE_PREV
diff --git a/nptl/pthread_kill.c b/nptl/pthread_kill.c
index 5d4c86f9205a6fb5..fb7862eff787a94f 100644
--- a/nptl/pthread_kill.c
+++ b/nptl/pthread_kill.c
@@ -16,6 +16,7 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
+#include <libc-lock.h>
#include <unistd.h>
#include <pthreadP.h>
#include <shlib-compat.h>
@@ -23,37 +24,51 @@
int
__pthread_kill_internal (pthread_t threadid, int signo)
{
- pid_t tid;
struct pthread *pd = (struct pthread *) threadid;
-
if (pd == THREAD_SELF)
- /* It is a special case to handle raise() implementation after a vfork
- call (which does not update the PD tid field). */
- tid = INLINE_SYSCALL_CALL (gettid);
- else
- /* Force load of pd->tid into local variable or register. Otherwise
- if a thread exits between ESRCH test and tgkill, we might return
- EINVAL, because pd->tid would be cleared by the kernel. */
- tid = atomic_forced_read (pd->tid);
-
- int val;
- if (__glibc_likely (tid > 0))
{
- pid_t pid = __getpid ();
-
- val = INTERNAL_SYSCALL_CALL (tgkill, pid, tid, signo);
- val = (INTERNAL_SYSCALL_ERROR_P (val)
- ? INTERNAL_SYSCALL_ERRNO (val) : 0);
+ /* Use the actual TID from the kernel, so that it refers to the
+ current thread even if called after vfork. There is no
+ signal blocking in this case, so that the signal is delivered
+ immediately, before __pthread_kill_internal returns: a signal
+ sent to the thread itself needs to be delivered
+ synchronously. (It is unclear if Linux guarantees the
+ delivery of all pending signals after unblocking in the code
+ below. POSIX only guarantees delivery of a single signal,
+ which may not be the right one.) */
+ pid_t tid = INTERNAL_SYSCALL_CALL (gettid);
+ int ret = INTERNAL_SYSCALL_CALL (kill, tid, signo);
+ return INTERNAL_SYSCALL_ERROR_P (ret) ? INTERNAL_SYSCALL_ERRNO (ret) : 0;
}
+
+ /* Block all signals, as required by pd->exit_lock. */
+ sigset_t old_mask;
+ __libc_signal_block_all (&old_mask);
+ __libc_lock_lock (pd->exit_lock);
+
+ int ret;
+ if (pd->exiting)
+ /* The thread is about to exit (or has exited). Sending the
+ signal is either not observable (the target thread has already
+ blocked signals at this point), or it will fail, or it might be
+ delivered to a new, unrelated thread that has reused the TID.
+ So do not actually send the signal. Do not report an error
+ because the threadid argument is still valid (the thread ID
+ lifetime has not ended), and ESRCH (for example) would be
+ misleading. */
+ ret = 0;
else
- /* The kernel reports that the thread has exited. POSIX specifies
- the ESRCH error only for the case when the lifetime of a thread
- ID has ended, but calling pthread_kill on such a thread ID is
- undefined in glibc. Therefore, do not treat kernel thread exit
- as an error. */
- val = 0;
+ {
+ /* Using tgkill is a safety measure. pd->exit_lock ensures that
+ the target thread cannot exit. */
+ ret = INTERNAL_SYSCALL_CALL (tgkill, __getpid (), pd->tid, signo);
+ ret = INTERNAL_SYSCALL_ERROR_P (ret) ? INTERNAL_SYSCALL_ERRNO (ret) : 0;
+ }
+
+ __libc_lock_unlock (pd->exit_lock);
+ __libc_signal_restore_set (&old_mask);
- return val;
+ return ret;
}
int
diff --git a/sysdeps/pthread/Makefile b/sysdeps/pthread/Makefile
index dedfa0d290da4949..48dba717a1cdc20a 100644
--- a/sysdeps/pthread/Makefile
+++ b/sysdeps/pthread/Makefile
@@ -119,7 +119,9 @@ tests += tst-cnd-basic tst-mtx-trylock tst-cnd-broadcast \
tst-unwind-thread \
tst-pt-vfork1 tst-pt-vfork2 tst-vfork1x tst-vfork2x \
tst-pthread_cancel-exited \
+ tst-pthread_cancel-select-loop \
tst-pthread_kill-exited \
+ tst-pthread_kill-exiting \
# tests
tests-time64 := \
diff --git a/sysdeps/pthread/tst-pthread_cancel-select-loop.c b/sysdeps/pthread/tst-pthread_cancel-select-loop.c
new file mode 100644
index 0000000000000000..a62087589cee24b5
--- /dev/null
+++ b/sysdeps/pthread/tst-pthread_cancel-select-loop.c
@@ -0,0 +1,87 @@
+/* Test that pthread_cancel succeeds during thread exit.
+ Copyright (C) 2021 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/>. */
+
+/* This test tries to trigger an internal race condition in
+ pthread_cancel, where the cancellation signal is sent after the
+ thread has begun the cancellation process. This can result in a
+ spurious ESRCH error. For the original bug 12889, the window is
+ quite small, so the bug was not reproduced in every run. */
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <support/check.h>
+#include <support/xthread.h>
+#include <support/xunistd.h>
+#include <sys/select.h>
+#include <unistd.h>
+
+/* Set to true by timeout_thread_function when the test should
+ terminate. */
+static bool timeout;
+
+static void *
+timeout_thread_function (void *unused)
+{
+ usleep (5 * 1000 * 1000);
+ __atomic_store_n (&timeout, true, __ATOMIC_RELAXED);
+ return NULL;
+}
+
+/* Used for blocking the select function below. */
+static int pipe_fds[2];
+
+static void *
+canceled_thread_function (void *unused)
+{
+ while (true)
+ {
+ fd_set rfs;
+ fd_set wfs;
+ fd_set efs;
+ FD_ZERO (&rfs);
+ FD_ZERO (&wfs);
+ FD_ZERO (&efs);
+ FD_SET (pipe_fds[0], &rfs);
+
+ /* If the cancellation request is recognized early, the thread
+ begins exiting while the cancellation signal arrives. */
+ select (FD_SETSIZE, &rfs, &wfs, &efs, NULL);
+ }
+ return NULL;
+}
+
+static int
+do_test (void)
+{
+ xpipe (pipe_fds);
+ pthread_t thr_timeout = xpthread_create (NULL, timeout_thread_function, NULL);
+
+ while (!__atomic_load_n (&timeout, __ATOMIC_RELAXED))
+ {
+ pthread_t thr = xpthread_create (NULL, canceled_thread_function, NULL);
+ xpthread_cancel (thr);
+ TEST_VERIFY (xpthread_join (thr) == PTHREAD_CANCELED);
+ }
+
+ xpthread_join (thr_timeout);
+ xclose (pipe_fds[0]);
+ xclose (pipe_fds[1]);
+ return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/pthread/tst-pthread_kill-exiting.c b/sysdeps/pthread/tst-pthread_kill-exiting.c
new file mode 100644
index 0000000000000000..f803e94f1195f204
--- /dev/null
+++ b/sysdeps/pthread/tst-pthread_kill-exiting.c
@@ -0,0 +1,123 @@
+/* Test that pthread_kill succeeds during thread exit.
+ Copyright (C) 2021 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/>. */
+
+/* This test verifies that pthread_kill for a thread that is exiting
+ succeeds (with or without actually delivering the signal). */
+
+#include <array_length.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <support/xsignal.h>
+#include <support/xthread.h>
+#include <unistd.h>
+
+/* Set to true by timeout_thread_function when the test should
+ terminate. */
+static bool timeout;
+
+static void *
+timeout_thread_function (void *unused)
+{
+ usleep (1000 * 1000);
+ __atomic_store_n (&timeout, true, __ATOMIC_RELAXED);
+ return NULL;
+}
+
+/* Used to synchronize the sending threads with the target thread and
+ main thread. */
+static pthread_barrier_t barrier_1;
+static pthread_barrier_t barrier_2;
+
+/* The target thread to which signals are to be sent. */
+static pthread_t target_thread;
+
+/* Set by the main thread to true after timeout has been set to
+ true. */
+static bool exiting;
+
+static void *
+sender_thread_function (void *unused)
+{
+ while (true)
+ {
+ /* Wait until target_thread has been initialized. The target
+ thread and main thread participate in this barrier. */
+ xpthread_barrier_wait (&barrier_1);
+
+ if (exiting)
+ break;
+
+ xpthread_kill (target_thread, SIGUSR1);
+
+ /* Communicate that the signal has been sent. The main thread
+ participates in this barrier. */
+ xpthread_barrier_wait (&barrier_2);
+ }
+ return NULL;
+}
+
+static void *
+target_thread_function (void *unused)
+{
+ target_thread = pthread_self ();
+ xpthread_barrier_wait (&barrier_1);
+ return NULL;
+}
+
+static int
+do_test (void)
+{
+ xsignal (SIGUSR1, SIG_IGN);
+
+ pthread_t thr_timeout = xpthread_create (NULL, timeout_thread_function, NULL);
+
+ pthread_t threads[4];
+ xpthread_barrier_init (&barrier_1, NULL, array_length (threads) + 2);
+ xpthread_barrier_init (&barrier_2, NULL, array_length (threads) + 1);
+
+ for (int i = 0; i < array_length (threads); ++i)
+ threads[i] = xpthread_create (NULL, sender_thread_function, NULL);
+
+ while (!__atomic_load_n (&timeout, __ATOMIC_RELAXED))
+ {
+ xpthread_create (NULL, target_thread_function, NULL);
+
+ /* Wait for the target thread to be set up and signal sending to
+ start. */
+ xpthread_barrier_wait (&barrier_1);
+
+ /* Wait for signal sending to complete. */
+ xpthread_barrier_wait (&barrier_2);
+
+ xpthread_join (target_thread);
+ }
+
+ exiting = true;
+
+ /* Signal the sending threads to exit. */
+ xpthread_create (NULL, target_thread_function, NULL);
+ xpthread_barrier_wait (&barrier_1);
+
+ for (int i = 0; i < array_length (threads); ++i)
+ xpthread_join (threads[i]);
+ xpthread_join (thr_timeout);
+
+ return 0;
+}
+
+#include <support/test-driver.c>