From: Gabriel-Andrew Pollo-Guilbert Date: Mon, 29 Jul 2019 22:05:35 +0000 (-0400) Subject: Fix: wait for initial statedump before proceeding to the main program X-Git-Tag: v2.12.0-rc1~28 X-Git-Url: http://git.liburcu.org/?p=lttng-ust.git;a=commitdiff_plain;h=eb0e6022d5e2621e0e0e50076ebe014c4e639411 Fix: wait for initial statedump before proceeding to the main program 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 Signed-off-by: Mathieu Desnoyers --- 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; }