diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c index 0356993c26..fa8100719f 100644 --- a/nptl/allocatestack.c +++ b/nptl/allocatestack.c @@ -31,6 +31,7 @@ #include #include #include +#include /* Default alignment of stack. */ #ifndef STACK_ALIGN @@ -126,6 +127,8 @@ 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 e1c8831f09..41ee56feb2 100644 --- a/nptl/descr.h +++ b/nptl/descr.h @@ -395,6 +395,12 @@ 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 7607f36e26..a559f86cc2 100644 --- a/nptl/pthread_create.c +++ b/nptl/pthread_create.c @@ -36,6 +36,7 @@ #include #include #include +#include #include @@ -484,6 +485,19 @@ 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 5d4c86f920..fb7862eff7 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 . */ +#include #include #include #include @@ -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; } - 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; - return val; + /* 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 + { + /* 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 ret; } int diff --git a/sysdeps/pthread/Makefile b/sysdeps/pthread/Makefile index dedfa0d290..48dba717a1 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 0000000000..a62087589c --- /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 + . */ + +/* 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 +#include +#include +#include +#include +#include +#include + +/* 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 diff --git a/sysdeps/pthread/tst-pthread_kill-exiting.c b/sysdeps/pthread/tst-pthread_kill-exiting.c new file mode 100644 index 0000000000..f803e94f11 --- /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 + . */ + +/* This test verifies that pthread_kill for a thread that is exiting + succeeds (with or without actually delivering the signal). */ + +#include +#include +#include +#include +#include +#include + +/* 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