/*
* SPDX-License-Identifier: LGPL-2.1-only
*
- * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
+ * Copyright (C) 2011 EfficiOS Inc.
* Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
*/
#include <lttng/ust-thread.h>
#include <lttng/ust-tracer.h>
#include <lttng/ust-common.h>
+#include <lttng/ust-cancelstate.h>
#include <urcu/tls-compat.h>
#include "lib/lttng-ust/futex.h"
#include "common/ustcomm.h"
*/
int lttng_ust_loaded __attribute__((weak));
+/*
+ * Notes on async-signal-safety of ust lock: a few libc functions are used
+ * which are not strictly async-signal-safe:
+ *
+ * - pthread_setcancelstate
+ * - pthread_mutex_lock
+ * - pthread_mutex_unlock
+ *
+ * As of glibc 2.35, the implementation of pthread_setcancelstate only
+ * touches TLS data, and it appears to be safe to use from signal
+ * handlers. If the libc implementation changes, this will need to be
+ * revisited, and we may ask glibc to provide an async-signal-safe
+ * pthread_setcancelstate.
+ *
+ * As of glibc 2.35, the implementation of pthread_mutex_lock/unlock
+ * for fast mutexes only relies on the pthread_mutex_t structure.
+ * Disabling signals around all uses of this mutex ensures
+ * signal-safety. If the libc implementation changes and eventually uses
+ * other global resources, this will need to be revisited and we may
+ * need to implement our own mutex.
+ */
+
/*
* Return 0 on success, -1 if should quit.
* The lock is taken in both cases.
int ust_lock(void)
{
sigset_t sig_all_blocked, orig_mask;
- int ret, oldstate;
+ int ret;
- ret = pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate);
- if (ret) {
- ERR("pthread_setcancelstate: %s", strerror(ret));
- }
- if (oldstate != PTHREAD_CANCEL_ENABLE) {
- ERR("pthread_setcancelstate: unexpected oldstate");
+ if (lttng_ust_cancelstate_disable_push()) {
+ ERR("lttng_ust_cancelstate_disable_push");
}
sigfillset(&sig_all_blocked);
ret = pthread_sigmask(SIG_SETMASK, &sig_all_blocked, &orig_mask);
if (ret) {
- ERR("pthread_sigmask: %s", strerror(ret));
+ ERR("pthread_sigmask: ret=%d", ret);
}
if (!URCU_TLS(ust_mutex_nest)++)
pthread_mutex_lock(&ust_mutex);
ret = pthread_sigmask(SIG_SETMASK, &orig_mask, NULL);
if (ret) {
- ERR("pthread_sigmask: %s", strerror(ret));
+ ERR("pthread_sigmask: ret=%d", ret);
}
if (lttng_ust_comm_should_quit) {
return -1;
void ust_lock_nocheck(void)
{
sigset_t sig_all_blocked, orig_mask;
- int ret, oldstate;
+ int ret;
- ret = pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate);
- if (ret) {
- ERR("pthread_setcancelstate: %s", strerror(ret));
- }
- if (oldstate != PTHREAD_CANCEL_ENABLE) {
- ERR("pthread_setcancelstate: unexpected oldstate");
+ if (lttng_ust_cancelstate_disable_push()) {
+ ERR("lttng_ust_cancelstate_disable_push");
}
sigfillset(&sig_all_blocked);
ret = pthread_sigmask(SIG_SETMASK, &sig_all_blocked, &orig_mask);
if (ret) {
- ERR("pthread_sigmask: %s", strerror(ret));
+ ERR("pthread_sigmask: ret=%d", ret);
}
if (!URCU_TLS(ust_mutex_nest)++)
pthread_mutex_lock(&ust_mutex);
ret = pthread_sigmask(SIG_SETMASK, &orig_mask, NULL);
if (ret) {
- ERR("pthread_sigmask: %s", strerror(ret));
+ ERR("pthread_sigmask: ret=%d", ret);
}
}
void ust_unlock(void)
{
sigset_t sig_all_blocked, orig_mask;
- int ret, oldstate;
+ int ret;
sigfillset(&sig_all_blocked);
ret = pthread_sigmask(SIG_SETMASK, &sig_all_blocked, &orig_mask);
if (ret) {
- ERR("pthread_sigmask: %s", strerror(ret));
+ ERR("pthread_sigmask: ret=%d", ret);
}
if (!--URCU_TLS(ust_mutex_nest))
pthread_mutex_unlock(&ust_mutex);
ret = pthread_sigmask(SIG_SETMASK, &orig_mask, NULL);
if (ret) {
- ERR("pthread_sigmask: %s", strerror(ret));
- }
- ret = pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, &oldstate);
- if (ret) {
- ERR("pthread_setcancelstate: %s", strerror(ret));
+ ERR("pthread_sigmask: ret=%d", ret);
}
- if (oldstate != PTHREAD_CANCEL_DISABLE) {
- ERR("pthread_setcancelstate: unexpected oldstate");
+ if (lttng_ust_cancelstate_disable_pop()) {
+ ERR("lttng_ust_cancelstate_disable_pop");
}
}
int statedump_pending;
int initial_statedump_done;
/* Keep procname for statedump */
- char procname[LTTNG_UST_ABI_PROCNAME_LEN];
+ char procname[LTTNG_UST_CONTEXT_PROCNAME_LEN];
};
/* Socket from app (connect) to session daemon (listen) for communication */
}
global_apps.allowed = 1;
- lttng_pthread_getname_np(global_apps.procname, LTTNG_UST_ABI_PROCNAME_LEN);
+ lttng_pthread_getname_np(global_apps.procname, LTTNG_UST_CONTEXT_PROCNAME_LEN);
error:
return ret;
}
goto end;
}
- lttng_pthread_getname_np(local_apps.procname, LTTNG_UST_ABI_PROCNAME_LEN);
+ lttng_pthread_getname_np(local_apps.procname, LTTNG_UST_CONTEXT_PROCNAME_LEN);
end:
return ret;
}
}
sock_info->root_handle = -1;
}
- sock_info->registration_done = 0;
- sock_info->initial_statedump_done = 0;
+
/*
* wait_shm_mmap, socket and notify socket are used by listener
if (exiting)
return;
+ sock_info->registration_done = 0;
+ sock_info->initial_statedump_done = 0;
+
if (sock_info->socket != -1) {
ret = ustcomm_close_unix_sock(sock_info->socket);
if (ret) {
DBG("Waiting for %s apps sessiond", sock_info->name);
/* Wait for futex wakeup */
- if (uatomic_read((int32_t *) sock_info->wait_shm_mmap))
- goto end_wait;
-
- while (lttng_ust_futex_async((int32_t *) sock_info->wait_shm_mmap,
- FUTEX_WAIT, 0, NULL, NULL, 0)) {
+ while (!uatomic_read((int32_t *) sock_info->wait_shm_mmap)) {
+ if (!lttng_ust_futex_async((int32_t *) sock_info->wait_shm_mmap, FUTEX_WAIT, 0, NULL, NULL, 0)) {
+ /*
+ * Prior queued wakeups queued by unrelated code
+ * using the same address can cause futex wait to
+ * return 0 even through the futex value is still
+ * 0 (spurious wakeups). Check the value again
+ * in user-space to validate whether it really
+ * differs from 0.
+ */
+ continue;
+ }
switch (errno) {
- case EWOULDBLOCK:
+ case EAGAIN:
/* Value already changed. */
goto end_wait;
case EINTR:
/* Retry if interrupted by signal. */
- break; /* Get out of switch. */
+ break; /* Get out of switch. Check again. */
case EFAULT:
wait_poll_fallback = 1;
DBG(
* Expose a canary symbol of the previous ABI to ensure we catch uses of a
* liblttng-ust.so.0 dlopen'd after .so.1 has been loaded. Use a different
* symbol than the detection code to ensure we don't detect ourself.
+ *
+ * This scheme will only work on systems where the global symbol table has
+ * priority when resolving the symbols of a dlopened shared object, which is
+ * the case on Linux but not on FreeBSD.
*/
void init_usterr(void);
void init_usterr(void)
* this library so it never becomes zero, thus never gets unloaded from the
* address space of the process. Since we are already running in the
* constructor of the LTTNG_UST_LIB_SONAME library, calling dlopen will
- * simply increment the refcount and no additionnal work is needed by the
+ * simply increment the refcount and no additional work is needed by the
* dynamic loader as the shared library is already loaded in the address
* space. As a safe guard, we use the RTLD_NODELETE flag to prevent
* unloading of the UST library if its refcount becomes zero (which should
return;
DBG("process %d", getpid());
lttng_ust_urcu_after_fork_parent();
- /* Release mutexes and reenable signals */
+ /* Release mutexes and re-enable signals */
ust_after_fork_common(restore_sigset);
}
/* Release urcu mutexes */
lttng_ust_urcu_after_fork_child();
lttng_ust_cleanup(0);
- /* Release mutexes and reenable signals */
+ /* Release mutexes and re-enable signals */
ust_after_fork_common(restore_sigset);
lttng_ust_ctor();
}
projects / lttng-ust.git / blobdiff