[lttng-dev] [PATCH lttng-ust v2] Fix: baddr_statedump deadlock with JUL tracing

[Mathieu Desnoyers]

----- Original Message -----
> From: "Paul Woegerer" <paul_woegerer at mentor.com>
> To: lttng-dev at lists.lttng.org, "mathieu desnoyers" <mathieu.desnoyers at efficios.com>, dgoulet at efficios.com
> Sent: Friday, November 29, 2013 2:32:54 PM
> Subject: [PATCH lttng-ust v2] Fix: baddr_statedump deadlock with JUL tracing

Almost there! I merged your patch, and then committed a fix that should handle
everything (missing ust lock around session iteration).

see commit

commit 37dddb65504eff070a64fb4a8f1c56ee81c3173c
Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
Date:   Sat Nov 30 15:42:50 2013 +0100

    Fix: take the ust lock around session iteration in statedump
    
    This is crafted _very_ carefully: we need to always take the ust lock
    _within_ the dynamic loader lock.
    
    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>

for details. Please let me know how this works for you.

Thanks!

Mathieu


> 
> Signed-off-by: Paul Woegerer <paul_woegerer at mentor.com>
> ---
>  include/lttng/ust-events.h       |  6 ++++++
>  liblttng-ust/lttng-events.c      | 19 ++++++++++++++++++-
>  liblttng-ust/lttng-tracer-core.h |  3 +--
>  liblttng-ust/lttng-ust-comm.c    | 30 +++++++++++++++++-------------
>  4 files changed, 42 insertions(+), 16 deletions(-)
> 
> diff --git a/include/lttng/ust-events.h b/include/lttng/ust-events.h
> index 5d43570..28f7391 100644
> --- a/include/lttng/ust-events.h
> +++ b/include/lttng/ust-events.h
> @@ -513,6 +513,9 @@ struct lttng_session {
>  	struct lttng_ust_event_ht events_ht;	/* ht of events */
>  	void *owner;				/* object owner */
>  	int tstate:1;				/* Transient enable state */
> +
> +	/* New UST 2.4 */
> +	int statedump_pending:1;
>  };
>  
>  struct lttng_transport {
> @@ -606,4 +609,7 @@ void lttng_filter_sync_state(struct
> lttng_bytecode_runtime *runtime);
>  struct cds_list_head *lttng_get_probe_list_head(void);
>  int lttng_session_active(void);
>  
> +typedef int (*t_statedump_func_ptr)(struct lttng_session *session);
> +int lttng_handle_pending_statedumps(t_statedump_func_ptr
> statedump_func_ptr);
> +
>  #endif /* _LTTNG_UST_EVENTS_H */
> diff --git a/liblttng-ust/lttng-events.c b/liblttng-ust/lttng-events.c
> index 7751584..9380e9c 100644
> --- a/liblttng-ust/lttng-events.c
> +++ b/liblttng-ust/lttng-events.c
> @@ -294,7 +294,8 @@ int lttng_session_enable(struct lttng_session *session)
>  	CMM_ACCESS_ONCE(session->active) = 1;
>  	CMM_ACCESS_ONCE(session->been_active) = 1;
>  
> -	lttng_ust_sockinfo_session_enabled(session->owner, session);
> +	session->statedump_pending = 1;
> +	lttng_ust_sockinfo_session_enabled(session->owner);
>  end:
>  	return ret;
>  }
> @@ -675,6 +676,22 @@ int lttng_fix_pending_events(void)
>  }
>  
>  /*
> + * Called after session enable: For each session, execute pending
> statedumps.
> + */
> +int lttng_handle_pending_statedumps(t_statedump_func_ptr statedump_func_ptr)
> +{
> +	struct lttng_session *session;
> +
> +	cds_list_for_each_entry(session, &sessions, node) {
> +		if (session->statedump_pending) {
> +			session->statedump_pending = 0;
> +			statedump_func_ptr(session);
> +		}
> +	}
> +	return 0;
> +}
> +
> +/*
>   * Only used internally at session destruction.
>   */
>  static
> diff --git a/liblttng-ust/lttng-tracer-core.h
> b/liblttng-ust/lttng-tracer-core.h
> index e7f549e..57df175 100644
> --- a/liblttng-ust/lttng-tracer-core.h
> +++ b/liblttng-ust/lttng-tracer-core.h
> @@ -45,7 +45,6 @@ const char *lttng_ust_obj_get_name(int id);
>  
>  int lttng_get_notify_socket(void *owner);
>  
> -void lttng_ust_sockinfo_session_enabled(void *owner,
> -		struct lttng_session *session_enabled);
> +void lttng_ust_sockinfo_session_enabled(void *owner);
>  
>  #endif /* _LTTNG_TRACER_CORE_H */
> diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
> index b99bf00..4724fab 100644
> --- a/liblttng-ust/lttng-ust-comm.c
> +++ b/liblttng-ust/lttng-ust-comm.c
> @@ -108,7 +108,7 @@ struct sock_info {
>  
>  	char wait_shm_path[PATH_MAX];
>  	char *wait_shm_mmap;
> -	struct lttng_session *session_enabled;
> +	int session_enabled;
>  };
>  
>  /* Socket from app (connect) to session daemon (listen) for communication */
> @@ -126,7 +126,7 @@ struct sock_info global_apps = {
>  
>  	.wait_shm_path = "/" LTTNG_UST_WAIT_FILENAME,
>  
> -	.session_enabled = NULL,
> +	.session_enabled = 0,
>  };
>  
>  /* TODO: allow global_apps_sock_path override */
> @@ -141,7 +141,7 @@ struct sock_info local_apps = {
>  	.socket = -1,
>  	.notify_socket = -1,
>  
> -	.session_enabled = NULL,
> +	.session_enabled = 0,
>  };
>  
>  static int wait_poll_fallback;
> @@ -709,6 +709,17 @@ error:
>  }
>  
>  static
> +void handle_pending_statedumps(struct sock_info *sock_info)
> +{
> +	int ctor_passed = sock_info->constructor_sem_posted;
> +
> +	if (ctor_passed && sock_info->session_enabled) {
> +		sock_info->session_enabled = 0;
> +		lttng_handle_pending_statedumps(&lttng_ust_baddr_statedump);
> +	}
> +}
> +
> +static
>  void cleanup_sock_info(struct sock_info *sock_info, int exiting)
>  {
>  	int ret;
> @@ -1214,13 +1225,7 @@ restart:
>  			if (ret) {
>  				ERR("Error handling message for %s socket", sock_info->name);
>  			} else {
> -				struct lttng_session *session;
> -
> -				session = sock_info->session_enabled;
> -				if (session) {
> -					sock_info->session_enabled = NULL;
> -					lttng_ust_baddr_statedump(session);
> -				}
> +				handle_pending_statedumps(sock_info);
>  			}
>  			continue;
>  		default:
> @@ -1535,9 +1540,8 @@ void ust_after_fork_child(sigset_t *restore_sigset)
>  	lttng_ust_init();
>  }
>  
> -void lttng_ust_sockinfo_session_enabled(void *owner,
> -		struct lttng_session *session_enabled)
> +void lttng_ust_sockinfo_session_enabled(void *owner)
>  {
>  	struct sock_info *sock_info = owner;
> -	sock_info->session_enabled = session_enabled;
> +	sock_info->session_enabled = 1;
>  }
> --
> 1.8.4
> 
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com