[lttng-dev] [PATCH lttng-ust v2] Fix: wait for initial statedump before proceeding to the main program
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Tue Jul 30 10:13:25 EDT 2019
Merged into master, 2.11, 2.10, 2.9, thanks!
Mathieu
----- On Jul 29, 2019, at 6:05 PM, Gabriel-Andrew Pollo-Guilbert gabriel.pollo-guilbert at efficios.com wrote:
> In the case of short lived applications, the application may exit before
> the initial statedump has completed.
>
> Higher-level trace analysis features such as translating addresses to
> symbols rely on statedump. That information is required for those
> analyses to work on such short-lived applications.
>
> Force the statedump to occur before handing the control to the
> application.
>
> Fixes #1190
>
> Signed-off-by: Gabriel-Andrew Pollo-Guilbert
> <gabriel.pollo-guilbert at efficios.com>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> ---
> v2:
> * renamed constructor_sem_posted -> registration_done
> * add sem_count_initial_value
> * add assert in decrement_sem_count()
> * edit documentation for handle_pending_statedump
> * reset registration_done and initial_statedump_done in cleanup_sock_info
>
> liblttng-ust/lttng-ust-comm.c | 88 ++++++++++++++++++++++++++---------
> 1 file changed, 67 insertions(+), 21 deletions(-)
>
> diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
> index a299ba84..0c6db9fe 100644
> --- a/liblttng-ust/lttng-ust-comm.c
> +++ b/liblttng-ust/lttng-ust-comm.c
> @@ -228,7 +228,11 @@ static sem_t constructor_wait;
> /*
> * Doing this for both the global and local sessiond.
> */
> -static int sem_count = { 2 };
> +enum {
> + sem_count_initial_value = 4,
> +};
> +
> +static int sem_count = sem_count_initial_value;
>
> /*
> * Counting nesting within lttng-ust. Used to ensure that calling fork()
> @@ -243,7 +247,7 @@ struct sock_info {
> const char *name;
> pthread_t ust_listener; /* listener thread */
> int root_handle;
> - int constructor_sem_posted;
> + int registration_done;
> int allowed;
> int global;
> int thread_active;
> @@ -256,6 +260,7 @@ struct sock_info {
> char *wait_shm_mmap;
> /* Keep track of lazy state dump not performed yet. */
> int statedump_pending;
> + int initial_statedump_done;
> };
>
> /* Socket from app (connect) to session daemon (listen) for communication */
> @@ -264,6 +269,7 @@ struct sock_info global_apps = {
> .global = 1,
>
> .root_handle = -1,
> + .registration_done = 0,
> .allowed = 0,
> .thread_active = 0,
>
> @@ -274,6 +280,7 @@ struct sock_info global_apps = {
> .wait_shm_path = "/" LTTNG_UST_WAIT_FILENAME,
>
> .statedump_pending = 0,
> + .initial_statedump_done = 0,
> };
>
> /* TODO: allow global_apps_sock_path override */
> @@ -282,6 +289,7 @@ struct sock_info local_apps = {
> .name = "local",
> .global = 0,
> .root_handle = -1,
> + .registration_done = 0,
> .allowed = 0, /* Check setuid bit first */
> .thread_active = 0,
>
> @@ -289,6 +297,7 @@ struct sock_info local_apps = {
> .notify_socket = -1,
>
> .statedump_pending = 0,
> + .initial_statedump_done = 0,
> };
>
> static int wait_poll_fallback;
> @@ -621,45 +630,81 @@ int send_reply(int sock, struct ustcomm_ust_reply *lur)
> }
>
> static
> -int handle_register_done(struct sock_info *sock_info)
> +void decrement_sem_count(unsigned int count)
> {
> int ret;
>
> - if (sock_info->constructor_sem_posted)
> - return 0;
> - sock_info->constructor_sem_posted = 1;
> + assert(uatomic_read(&sem_count) >= count);
> +
> if (uatomic_read(&sem_count) <= 0) {
> - return 0;
> + return;
> }
> - ret = uatomic_add_return(&sem_count, -1);
> +
> + ret = uatomic_add_return(&sem_count, -count);
> if (ret == 0) {
> ret = sem_post(&constructor_wait);
> assert(!ret);
> }
> +}
> +
> +static
> +int handle_register_done(struct sock_info *sock_info)
> +{
> + if (sock_info->registration_done)
> + return 0;
> + sock_info->registration_done = 1;
> +
> + decrement_sem_count(1);
> +
> + return 0;
> +}
> +
> +static
> +int handle_register_failed(struct sock_info *sock_info)
> +{
> + if (sock_info->registration_done)
> + return 0;
> + sock_info->registration_done = 1;
> + sock_info->initial_statedump_done = 1;
> +
> + decrement_sem_count(2);
> +
> return 0;
> }
>
> /*
> * Only execute pending statedump after the constructor semaphore has
> - * been posted by each listener thread. This means statedump will only
> - * be performed after the "registration done" command is received from
> - * each session daemon the application is connected to.
> + * been posted by the current listener thread. This means statedump will
> + * only be performed after the "registration done" command is received
> + * from this thread's session daemon.
> *
> * This ensures we don't run into deadlock issues with the dynamic
> * loader mutex, which is held while the constructor is called and
> * waiting on the constructor semaphore. All operations requiring this
> * dynamic loader lock need to be postponed using this mechanism.
> + *
> + * In a scenario with two session daemons connected to the application,
> + * it is possible that the first listener thread which receives the
> + * registration done command issues its statedump while the dynamic
> + * loader lock is still held by the application constructor waiting on
> + * the semaphore. It will however be allowed to proceed when the
> + * second session daemon sends the registration done command to the
> + * second listener thread. This situation therefore does not produce
> + * a deadlock.
> */
> static
> void handle_pending_statedump(struct sock_info *sock_info)
> {
> - int ctor_passed = sock_info->constructor_sem_posted;
> -
> - if (ctor_passed && sock_info->statedump_pending) {
> + if (sock_info->registration_done && sock_info->statedump_pending) {
> sock_info->statedump_pending = 0;
> pthread_mutex_lock(&ust_fork_mutex);
> lttng_handle_pending_statedump(sock_info);
> pthread_mutex_unlock(&ust_fork_mutex);
> +
> + if (!sock_info->initial_statedump_done) {
> + sock_info->initial_statedump_done = 1;
> + decrement_sem_count(1);
> + }
> }
> }
>
> @@ -1069,7 +1114,8 @@ void cleanup_sock_info(struct sock_info *sock_info, int
> exiting)
> }
> sock_info->root_handle = -1;
> }
> - sock_info->constructor_sem_posted = 0;
> + sock_info->registration_done = 0;
> + sock_info->initial_statedump_done = 0;
>
> /*
> * wait_shm_mmap, socket and notify socket are used by listener
> @@ -1477,7 +1523,7 @@ restart:
> * If we cannot find the sessiond daemon, don't delay
> * constructor execution.
> */
> - ret = handle_register_done(sock_info);
> + ret = handle_register_failed(sock_info);
> assert(!ret);
> ust_unlock();
> goto restart;
> @@ -1531,7 +1577,7 @@ restart:
> * If we cannot register to the sessiond daemon, don't
> * delay constructor execution.
> */
> - ret = handle_register_done(sock_info);
> + ret = handle_register_failed(sock_info);
> assert(!ret);
> ust_unlock();
> goto restart;
> @@ -1560,7 +1606,7 @@ restart:
> * If we cannot find the sessiond daemon, don't delay
> * constructor execution.
> */
> - ret = handle_register_done(sock_info);
> + ret = handle_register_failed(sock_info);
> assert(!ret);
> ust_unlock();
> goto restart;
> @@ -1624,7 +1670,7 @@ restart:
> * If we cannot register to the sessiond daemon, don't
> * delay constructor execution.
> */
> - ret = handle_register_done(sock_info);
> + ret = handle_register_failed(sock_info);
> assert(!ret);
> ust_unlock();
> goto restart;
> @@ -1654,7 +1700,7 @@ restart:
> * If we cannot register to the sessiond daemon, don't
> * delay constructor execution.
> */
> - ret = handle_register_done(sock_info);
> + ret = handle_register_failed(sock_info);
> assert(!ret);
> ust_unlock();
> goto end;
> @@ -1923,7 +1969,7 @@ void lttng_ust_cleanup(int exiting)
> exit_tracepoint();
> if (!exiting) {
> /* Reinitialize values for fork */
> - sem_count = 2;
> + sem_count = sem_count_initial_value;
> lttng_ust_comm_should_quit = 0;
> initialized = 0;
> }
> --
> 2.22.0
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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