[dm-devel] [PATCH v2] multipathd: fix compilation issue with liburcu < 0.8

[Benjamin Marzinski]

On Thu, May 13, 2021 at 09:53:58PM +0200, mwilck at suse.com wrote:
> From: Martin Wilck <mwilck at suse.com>
> 
> To avoid race conditions with pending RCU callbacks on exit, it's
> necessary to call rcu_barrier() in cleanup_rcu() (see
> https://lists.lttng.org/pipermail/lttng-dev/2021-May/029958.html and
> follow-ups).
> 
> rcu_barrier() is only available in User-space RCU v0.8 and newer.
> Fix it by reverting 5d0dae6 ("multipathd: Fix liburcu memory leak")
> if an older version of liburcu is detected.
> 
> Fixes: 5d0dae6 ("multipathd: Fix liburcu memory leak")
> Signed-off-by: Martin Wilck <mwilck at suse.com>
Reviewed-by: Benjamin Marzinski <bmarzins at redhat.com>
> 
> ---
> v2: Use $(PKGCONFIG) (Ben Marzinski); remove "\n" in awk.
> 
> ---
>  multipathd/Makefile |  2 ++
>  multipathd/main.c   | 17 +++++++++++++++--
>  2 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/multipathd/Makefile b/multipathd/Makefile
> index d053c1e..393b6cb 100644
> --- a/multipathd/Makefile
> +++ b/multipathd/Makefile
> @@ -16,6 +16,8 @@ LDFLAGS += $(BIN_LDFLAGS)
>  LIBDEPS += -L$(multipathdir) -lmultipath -L$(mpathpersistdir) -lmpathpersist \
>  	   -L$(mpathcmddir) -lmpathcmd -ludev -ldl -lurcu -lpthread \
>  	   -ldevmapper -lreadline
> +CFLAGS += $(shell $(PKGCONFIG) --modversion liburcu 2>/dev/null | \
> +	awk -F. '{ printf("-DURCU_VERSION=0x%06x", 256 * ( 256 * $$1 + $$2) + $$3); }')
>  
>  ifdef SYSTEMD
>  	CFLAGS += -DUSE_SYSTEMD=$(SYSTEMD)
> diff --git a/multipathd/main.c b/multipathd/main.c
> index 102946b..c34fd9c 100644
> --- a/multipathd/main.c
> +++ b/multipathd/main.c
> @@ -3031,6 +3031,10 @@ static void cleanup_threads(void)
>  	pthread_attr_destroy(&waiter_attr);
>  }
>  
> +#ifndef URCU_VERSION
> +#  define URCU_VERSION 0
> +#endif
> +#if (URCU_VERSION >= 0x000800)
>  /*
>   * Use a non-default call_rcu_data for child().
>   *
> @@ -3040,6 +3044,9 @@ static void cleanup_threads(void)
>   * can't be joined with pthread_join(), leaving a memory leak.
>   *
>   * Therefore we create our own, which can be destroyed and joined.
> + * The cleanup handler needs to call rcu_barrier(), which is only
> + * available in user-space RCU v0.8 and newer. See
> + * https://lists.lttng.org/pipermail/lttng-dev/2021-May/029958.html
>   */
>  static struct call_rcu_data *setup_rcu(void)
>  {
> @@ -3072,6 +3079,7 @@ static void cleanup_rcu(void)
>  	}
>  	rcu_unregister_thread();
>  }
> +#endif /* URCU_VERSION */
>  
>  static void cleanup_child(void)
>  {
> @@ -3116,9 +3124,14 @@ child (__attribute__((unused)) void *param)
>  	init_unwinder();
>  	mlockall(MCL_CURRENT | MCL_FUTURE);
>  	signal_init();
> +#if (URCU_VERSION >= 0x000800)
>  	mp_rcu_data = setup_rcu();
> -
> -	if (atexit(cleanup_rcu) || atexit(cleanup_child))
> +	if (atexit(cleanup_rcu))
> +		fprintf(stderr, "failed to register RCU cleanup handler\n");
> +#else
> +	rcu_init();
> +#endif
> +	if (atexit(cleanup_child))
>  		fprintf(stderr, "failed to register cleanup handlers\n");
>  
>  	setup_thread_attr(&misc_attr, 64 * 1024, 0);
> -- 
> 2.31.1