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make jl_thread_suspend_and_get_state safe #55500

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Aug 20, 2024
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make jl_thread_suspend_and_get_state safe #55500

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109 changes: 55 additions & 54 deletions src/signals-unix.c
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Original file line number Diff line number Diff line change
Expand Up @@ -314,6 +314,8 @@ int exc_reg_is_write_fault(uintptr_t esr) {
#if defined(HAVE_MACH)
#include "signals-mach.c"
#else
#include <poll.h>
#include <sys/eventfd.h>

int jl_lock_stackwalk(void)
{
Expand Down Expand Up @@ -439,17 +441,13 @@ JL_NO_ASAN static void segv_handler(int sig, siginfo_t *info, void *context)
}
}

#if !defined(JL_DISABLE_LIBUNWIND)
static bt_context_t *signal_context;
pthread_mutex_t in_signal_lock;
static pthread_cond_t exit_signal_cond;
static pthread_cond_t signal_caught_cond;
pthread_mutex_t in_signal_lock; // shared with jl_delete_thread
static bt_context_t *signal_context; // protected by in_signal_lock
static int exit_signal_cond = -1;
static int signal_caught_cond = -1;

int jl_thread_suspend_and_get_state(int tid, int timeout, bt_context_t *ctx)
{
struct timespec ts;
clock_gettime(CLOCK_REALTIME, &ts);
ts.tv_sec += timeout;
pthread_mutex_lock(&in_signal_lock);
jl_ptls_t ptls2 = jl_atomic_load_relaxed(&jl_all_tls_states)[tid];
jl_task_t *ct2 = ptls2 ? jl_atomic_load_relaxed(&ptls2->current_task) : NULL;
Expand All @@ -458,48 +456,51 @@ int jl_thread_suspend_and_get_state(int tid, int timeout, bt_context_t *ctx)
pthread_mutex_unlock(&in_signal_lock);
return 0;
}
jl_atomic_store_release(&ptls2->signal_request, 1);
pthread_kill(ptls2->system_id, SIGUSR2);
// wait for thread to acknowledge
int err = pthread_cond_timedwait(&signal_caught_cond, &in_signal_lock, &ts);
if (err == ETIMEDOUT) {
sig_atomic_t request = 1;
sig_atomic_t request = 0;
if (!jl_atomic_cmpswap(&ptls2->signal_request, &request, 1)) {
// something is wrong, or there is already a usr2 in flight elsewhere
pthread_mutex_unlock(&in_signal_lock);
return 0;
}
request = 1;
int err = pthread_kill(ptls2->system_id, SIGUSR2);
// wait for thread to acknowledge or timeout
struct pollfd event = {signal_caught_cond, POLLIN, 0};
if (err == 0) {
do {
err = poll(&event, 1, timeout * 1000);
} while (err == -1 && errno == EINTR);
}
if ((event.revents & POLLIN) == 0) {
// not ready after timeout: try to cancel this request
if (jl_atomic_cmpswap(&ptls2->signal_request, &request, 0)) {
pthread_mutex_unlock(&in_signal_lock);
return 0;
}
// Request is either now 0 (meaning the other thread is waiting for
// exit_signal_cond already),
// Or it is now -1 (meaning the other thread
// is waiting for in_signal_lock, and we need to release that lock
// here for a bit, until the other thread has a chance to get to the
// exit_signal_cond)
if (request == -1) {
err = pthread_cond_wait(&signal_caught_cond, &in_signal_lock);
assert(!err);
}
}
eventfd_t got;
do {
err = read(signal_caught_cond, &got, sizeof(eventfd_t));
} while (err == -1 && errno == EINTR);
if (err != sizeof(eventfd_t)) abort();
assert(got == 1); (void) got;
// Now the other thread is waiting on exit_signal_cond (verify that here by
// checking it is 0, and add an acquire barrier for good measure)
int request = jl_atomic_load_acquire(&ptls2->signal_request);
request = jl_atomic_load_acquire(&ptls2->signal_request);
assert(request == 0); (void) request;
jl_atomic_store_release(&ptls2->signal_request, 1); // prepare to resume normally
jl_atomic_store_release(&ptls2->signal_request, 4); // prepare to resume normally, but later code may change this
*ctx = *signal_context;
return 1;
}

void jl_thread_resume(int tid)
{
jl_ptls_t ptls2 = jl_atomic_load_relaxed(&jl_all_tls_states)[tid];
pthread_cond_broadcast(&exit_signal_cond);
pthread_cond_wait(&signal_caught_cond, &in_signal_lock); // wait for thread to acknowledge (so that signal_request doesn't get mixed up)
// The other thread is waiting to leave exit_signal_cond (verify that here by
// checking it is 0, and add an acquire barrier for good measure)
int request = jl_atomic_load_acquire(&ptls2->signal_request);
assert(request == 0); (void) request;
int err;
eventfd_t got = 1;
err = write(exit_signal_cond, &got, sizeof(eventfd_t));
if (err != sizeof(eventfd_t)) abort();
pthread_mutex_unlock(&in_signal_lock);
}
#endif

// Throw jl_interrupt_exception if the master thread is in a signal async region
// or if SIGINT happens too often.
Expand All @@ -508,9 +509,11 @@ static void jl_try_deliver_sigint(void)
jl_ptls_t ptls2 = jl_atomic_load_relaxed(&jl_all_tls_states)[0];
jl_safepoint_enable_sigint();
jl_wake_libuv();
pthread_mutex_lock(&in_signal_lock);
jl_atomic_store_release(&ptls2->signal_request, 2);
// This also makes sure `sleep` is aborted.
pthread_kill(ptls2->system_id, SIGUSR2);
pthread_mutex_unlock(&in_signal_lock);
}

// Write only by signal handling thread, read only by main thread
Expand Down Expand Up @@ -543,12 +546,12 @@ static void jl_exit_thread0(int signo, jl_bt_element_t *bt_data, size_t bt_size)
}

// request:
// -1: beginning processing [invalid outside here]
// 0: nothing [not from here]
// 1: get state
// 1: get state & wait for request
// 2: throw sigint if `!defer_signal && io_wait` or if force throw threshold
// is reached
// 3: raise `thread0_exit_signo` and try to exit
// 4: no-op
void usr2_handler(int sig, siginfo_t *info, void *ctx)
{
jl_task_t *ct = jl_get_current_task();
Expand All @@ -559,25 +562,21 @@ void usr2_handler(int sig, siginfo_t *info, void *ctx)
return;
int errno_save = errno;
// acknowledge that we saw the signal_request
sig_atomic_t request = jl_atomic_exchange(&ptls->signal_request, -1);
#if !defined(JL_DISABLE_LIBUNWIND)
sig_atomic_t request = jl_atomic_exchange(&ptls->signal_request, 0);
if (request == 1) {
pthread_mutex_lock(&in_signal_lock);
signal_context = jl_to_bt_context(ctx);
// acknowledge that we set the signal_caught_cond broadcast
int err;
eventfd_t got = 1;
err = write(signal_caught_cond, &got, sizeof(eventfd_t));
if (err != sizeof(eventfd_t)) abort();
do {
err = read(exit_signal_cond, &got, sizeof(eventfd_t));
} while (err == -1 && errno == EINTR);
if (err != sizeof(eventfd_t)) abort();
assert(got == 1);
request = jl_atomic_exchange(&ptls->signal_request, 0);
assert(request == -1); (void) request;
pthread_cond_broadcast(&signal_caught_cond);
pthread_cond_wait(&exit_signal_cond, &in_signal_lock);
request = jl_atomic_exchange(&ptls->signal_request, 0);
assert(request == 1 || request == 3);
// acknowledge that we got the resume signal
pthread_cond_broadcast(&signal_caught_cond);
pthread_mutex_unlock(&in_signal_lock);
assert(request == 2 || request == 3 || request == 4);
}
else
#endif
jl_atomic_exchange(&ptls->signal_request, 0); // returns -1
if (request == 2) {
int force = jl_check_force_sigint();
if (force || (!ptls->defer_signal && ptls->io_wait)) {
Expand Down Expand Up @@ -1038,10 +1037,12 @@ void restore_signals(void)
jl_sigsetset(&sset);
pthread_sigmask(SIG_SETMASK, &sset, 0);

#if !defined(HAVE_MACH) && !defined(JL_DISABLE_LIBUNWIND)
#if !defined(HAVE_MACH)
exit_signal_cond = eventfd(0, EFD_CLOEXEC);
signal_caught_cond = eventfd(0, EFD_CLOEXEC);
if (pthread_mutex_init(&in_signal_lock, NULL) != 0 ||
pthread_cond_init(&exit_signal_cond, NULL) != 0 ||
pthread_cond_init(&signal_caught_cond, NULL) != 0) {
exit_signal_cond == -1 ||
signal_caught_cond == -1) {
jl_error("SIGUSR pthread init failed");
}
#endif
Expand Down