[lttng-dev] [PATCH lttng-ust] Perform the sem_wait on the constructor semaphore just before the main

[Mathieu Desnoyers]

Can you extend the changelog by any chance, for instance by
explaining why we need this ? Something along the lines of
fixing deadlocks involving the glibc internal dynamic loader
lock would be good.

Thanks,

Mathieu

----- Original Message -----
> From: "Jérémie Galarneau" <jeremie.galarneau at efficios.com>
> To: lttng-dev at lists.lttng.org
> Cc: "mathieu desnoyers" <mathieu.desnoyers at efficios.com>, "Jérémie Galarneau" <jeremie.galarneau at efficios.com>
> Sent: Saturday, November 15, 2014 8:12:38 PM
> Subject: [PATCH lttng-ust] Perform the sem_wait on the constructor semaphore just before the main
> 
> Signed-off-by: Jérémie Galarneau <jeremie.galarneau at efficios.com>
> ---
>  liblttng-ust/Makefile.am      |  7 ++++
>  liblttng-ust/lttng-ust-comm.c | 75
>  ++++++++++++++++++++++++++++---------------
>  2 files changed, 56 insertions(+), 26 deletions(-)
> 
> diff --git a/liblttng-ust/Makefile.am b/liblttng-ust/Makefile.am
> index e2e1baa..802d32d 100644
> --- a/liblttng-ust/Makefile.am
> +++ b/liblttng-ust/Makefile.am
> @@ -83,4 +83,11 @@ liblttng_ust_la_LIBADD = \
>  	liblttng-ust-tracepoint.la \
>  	liblttng-ust-runtime.la liblttng-ust-support.la
>  
> +if LTTNG_UST_BUILD_WITH_LIBDL
> +liblttng_ust_la_LIBADD += -ldl
> +endif
> +if LTTNG_UST_BUILD_WITH_LIBC_DL
> +liblttng_ust_la_LIBADD += -lc
> +endif
> +
>  liblttng_ust_la_CFLAGS = -DUST_COMPONENT="liblttng_ust" -fno-strict-aliasing
> diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
> index 3df2adc..8258e85 100644
> --- a/liblttng-ust/lttng-ust-comm.c
> +++ b/liblttng-ust/lttng-ust-comm.c
> @@ -20,6 +20,7 @@
>   */
>  
>  #define _LGPL_SOURCE
> +#define _GNU_SOURCE
>  #include <sys/types.h>
>  #include <sys/socket.h>
>  #include <sys/mman.h>
> @@ -52,6 +53,7 @@
>  #include "compat.h"
>  #include "../libringbuffer/tlsfixup.h"
>  #include "lttng-ust-baddr.h"
> +#include <lttng/ust-dlfcn.h>
>  
>  /*
>   * Has lttng ust comm constructor been called ?
> @@ -1405,10 +1407,8 @@ void lttng_ust_malloc_wrapper_init(void)
>   */
>  void __attribute__((constructor)) lttng_ust_init(void)
>  {
> -	struct timespec constructor_timeout;
>  	sigset_t sig_all_blocked, orig_parent_mask;
>  	pthread_attr_t thread_attr;
> -	int timeout_mode;
>  	int ret;
>  
>  	if (uatomic_xchg(&initialized, 1) == 1)
> @@ -1446,8 +1446,6 @@ void __attribute__((constructor)) lttng_ust_init(void)
>  	 */
>  	lttng_ust_malloc_wrapper_init();
>  
> -	timeout_mode = get_constructor_timeout(&constructor_timeout);
> -
>  	ret = sem_init(&constructor_wait, 0, 0);
>  	assert(!ret);
>  
> @@ -1507,28 +1505,6 @@ void __attribute__((constructor)) lttng_ust_init(void)
>  	if (ret) {
>  		ERR("pthread_sigmask: %s", strerror(ret));
>  	}
> -
> -	switch (timeout_mode) {
> -	case 1:	/* timeout wait */
> -		do {
> -			ret = sem_timedwait(&constructor_wait,
> -					&constructor_timeout);
> -		} while (ret < 0 && errno == EINTR);
> -		if (ret < 0 && errno == ETIMEDOUT) {
> -			ERR("Timed out waiting for lttng-sessiond");
> -		} else {
> -			assert(!ret);
> -		}
> -		break;
> -	case -1:/* wait forever */
> -		do {
> -			ret = sem_wait(&constructor_wait);
> -		} while (ret < 0 && errno == EINTR);
> -		assert(!ret);
> -		break;
> -	case 0:	/* no timeout */
> -		break;
> -	}
>  }
>  
>  static
> @@ -1703,3 +1679,50 @@ void lttng_ust_sockinfo_session_enabled(void *owner)
>  	struct sock_info *sock_info = owner;
>  	sock_info->statedump_pending = 1;
>  }
> +
> +int __libc_start_main(int (*main) (int, char **, char **), int argc,
> +	char **ubp_av, void (*init) (void), void (*fini) (void),
> +	void (*rtld_fini) (void), void (*stack_end))
> +{
> +	int ret;
> +	int timeout_mode;
> +	struct timespec constructor_timeout;
> +	int (*libc_main_func)(int (*main) (int, char **, char **),
> +		int argc, char **ubp_av, void (*init) (void),
> +		void (*fini) (void), void (*rtld_fini) (void),
> +		void (*stack_end));
> +
> +	/* Retrieve the original __libc_start_main function */
> +	libc_main_func = dlsym(RTLD_NEXT, "__libc_start_main");
> +	if (libc_main_func == NULL) {
> +		ERR("unable to find \"__libc_start_main\" symbol\n");
> +		errno = ENOSYS;
> +		return -1;
> +	}
> +
> +	timeout_mode = get_constructor_timeout(&constructor_timeout);
> +	switch (timeout_mode) {
> +	case 1:	/* timeout wait */
> +		do {
> +			ret = sem_timedwait(&constructor_wait,
> +					&constructor_timeout);
> +		} while (ret < 0 && errno == EINTR);
> +		if (ret < 0 && errno == ETIMEDOUT) {
> +			ERR("Timed out waiting for lttng-sessiond");
> +		} else {
> +			assert(!ret);
> +		}
> +		break;
> +	case -1:/* wait forever */
> +		do {
> +			ret = sem_wait(&constructor_wait);
> +		} while (ret < 0 && errno == EINTR);
> +		assert(!ret);
> +		break;
> +	case 0:	/* no timeout */
> +		break;
> +	}
> +
> +	/* Call the original function */
> +	return libc_main_func(main, argc, ubp_av, init, fini, rtld_fini,
> stack_end);
> +}
> --
> 2.1.3
> 
> 

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