Re: [PATCH RFC V4 1/6] perf tools: lock to protect namespaces and comm list

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Fri, Sep 29, 2017 at 07:47:52AM -0700, kan.liang@intel.com escreveu:
> From: Kan Liang <kan.liang@intel.com>
> 
> Add two locks to protect namespaces_list and comm_list.
> 
> The lock is only needed for multithreaded code, so using mutex wrappers
> provided by perf tool.
> 
> Not all the comm_list/namespaces_list accessing are protected, e.g.
> thread__exec_comm. Because the multithread code for perf top event
> synthesizing does not touch them. They don't need a lock.

They don't need a lock _now_, ok I think we can proceed that way, this
cset should serve as a warning to people working in further
multithreading perf.

- Arnaldo
 
> Signed-off-by: Kan Liang <kan.liang@intel.com>
> ---
>  tools/perf/util/thread.c | 53 +++++++++++++++++++++++++++++++++++++++++++-----
>  tools/perf/util/thread.h |  3 +++
>  2 files changed, 51 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
> index c09bdb5..bf73117 100644
> --- a/tools/perf/util/thread.c
> +++ b/tools/perf/util/thread.c
> @@ -45,6 +45,8 @@ struct thread *thread__new(pid_t pid, pid_t tid)
>  		thread->cpu = -1;
>  		INIT_LIST_HEAD(&thread->namespaces_list);
>  		INIT_LIST_HEAD(&thread->comm_list);
> +		init_rwsem(&thread->namespaces_lock);
> +		init_rwsem(&thread->comm_lock);
>  
>  		comm_str = malloc(32);
>  		if (!comm_str)
> @@ -83,18 +85,26 @@ void thread__delete(struct thread *thread)
>  		map_groups__put(thread->mg);
>  		thread->mg = NULL;
>  	}
> +	down_write(&thread->namespaces_lock);
>  	list_for_each_entry_safe(namespaces, tmp_namespaces,
>  				 &thread->namespaces_list, list) {
>  		list_del(&namespaces->list);
>  		namespaces__free(namespaces);
>  	}
> +	up_write(&thread->namespaces_lock);
> +
> +	down_write(&thread->comm_lock);
>  	list_for_each_entry_safe(comm, tmp_comm, &thread->comm_list, list) {
>  		list_del(&comm->list);
>  		comm__free(comm);
>  	}
> +	up_write(&thread->comm_lock);
> +
>  	unwind__finish_access(thread);
>  	nsinfo__zput(thread->nsinfo);
>  
> +	exit_rwsem(&thread->namespaces_lock);
> +	exit_rwsem(&thread->comm_lock);
>  	free(thread);
>  }
>  
> @@ -125,8 +135,8 @@ struct namespaces *thread__namespaces(const struct thread *thread)
>  	return list_first_entry(&thread->namespaces_list, struct namespaces, list);
>  }
>  
> -int thread__set_namespaces(struct thread *thread, u64 timestamp,
> -			   struct namespaces_event *event)
> +static int __thread__set_namespaces(struct thread *thread, u64 timestamp,
> +				    struct namespaces_event *event)
>  {
>  	struct namespaces *new, *curr = thread__namespaces(thread);
>  
> @@ -149,6 +159,17 @@ int thread__set_namespaces(struct thread *thread, u64 timestamp,
>  	return 0;
>  }
>  
> +int thread__set_namespaces(struct thread *thread, u64 timestamp,
> +			   struct namespaces_event *event)
> +{
> +	int ret;
> +
> +	down_write(&thread->namespaces_lock);
> +	ret = __thread__set_namespaces(thread, timestamp, event);
> +	up_write(&thread->namespaces_lock);
> +	return ret;
> +}
> +
>  struct comm *thread__comm(const struct thread *thread)
>  {
>  	if (list_empty(&thread->comm_list))
> @@ -170,8 +191,8 @@ struct comm *thread__exec_comm(const struct thread *thread)
>  	return last;
>  }
>  
> -int __thread__set_comm(struct thread *thread, const char *str, u64 timestamp,
> -		       bool exec)
> +static int ____thread__set_comm(struct thread *thread, const char *str,
> +				u64 timestamp, bool exec)
>  {
>  	struct comm *new, *curr = thread__comm(thread);
>  
> @@ -195,6 +216,17 @@ int __thread__set_comm(struct thread *thread, const char *str, u64 timestamp,
>  	return 0;
>  }
>  
> +int __thread__set_comm(struct thread *thread, const char *str, u64 timestamp,
> +		       bool exec)
> +{
> +	int ret;
> +
> +	down_write(&thread->comm_lock);
> +	ret = ____thread__set_comm(thread, str, timestamp, exec);
> +	up_write(&thread->comm_lock);
> +	return ret;
> +}
> +
>  int thread__set_comm_from_proc(struct thread *thread)
>  {
>  	char path[64];
> @@ -212,7 +244,7 @@ int thread__set_comm_from_proc(struct thread *thread)
>  	return err;
>  }
>  
> -const char *thread__comm_str(const struct thread *thread)
> +static const char *__thread__comm_str(const struct thread *thread)
>  {
>  	const struct comm *comm = thread__comm(thread);
>  
> @@ -222,6 +254,17 @@ const char *thread__comm_str(const struct thread *thread)
>  	return comm__str(comm);
>  }
>  
> +const char *thread__comm_str(const struct thread *thread)
> +{
> +	const char *str;
> +
> +	down_read((struct rw_semaphore *)&thread->comm_lock);
> +	str = __thread__comm_str(thread);
> +	up_read((struct rw_semaphore *)&thread->comm_lock);
> +
> +	return str;
> +}
> +
>  /* CHECKME: it should probably better return the max comm len from its comm list */
>  int thread__comm_len(struct thread *thread)
>  {
> diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
> index cb1a5dd..10555d6 100644
> --- a/tools/perf/util/thread.h
> +++ b/tools/perf/util/thread.h
> @@ -9,6 +9,7 @@
>  #include "symbol.h"
>  #include <strlist.h>
>  #include <intlist.h>
> +#include "rwsem.h"
>  
>  struct thread_stack;
>  struct unwind_libunwind_ops;
> @@ -29,7 +30,9 @@ struct thread {
>  	int			comm_len;
>  	bool			dead; /* if set thread has exited */
>  	struct list_head	namespaces_list;
> +	struct rw_semaphore	namespaces_lock;
>  	struct list_head	comm_list;
> +	struct rw_semaphore	comm_lock;
>  	u64			db_id;
>  
>  	void			*priv;
> -- 
> 2.5.5