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Date:	Mon, 14 Jul 2014 17:18:29 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 02/41] perf tools: Fix map groups of threads with unknown
 pids

Em Mon, Jul 14, 2014 at 01:02:26PM +0300, Adrian Hunter escreveu:
> Events like sched_switch do not provide a pid (tgid)
> which can result in threads with an unknown pid.  If
> the pid is later discovered, join the map groups.
> Note the thread's map groups should be empty because
> they are populated by MMAP events which do provide the
> pid and tid.
> 
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---
>  tools/perf/util/machine.c | 22 ++++++++++++++++------
>  tools/perf/util/map.c     | 14 ++++++++++++++
>  tools/perf/util/map.h     |  1 +
>  tools/perf/util/thread.c  | 35 +++++++++++++++++++++++++++++++++++
>  tools/perf/util/thread.h  |  1 +
>  5 files changed, 67 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index 5b80877..0fa93c1 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -272,6 +272,17 @@ void machines__set_id_hdr_size(struct machines *machines, u16 id_hdr_size)
>  	return;
>  }
>  
> +static void machine__update_thread_pid(struct machine *machine,
> +				       struct thread *th, pid_t pid)
> +{
> +	if (pid != th->pid_ && pid != -1 && th->pid_ == -1) {
> +		th->pid_ = pid;
> +		if (thread__join_map_groups(th, machine))
> +			pr_err("Failed to join map groups for %d:%d\n",
> +			       th->pid_, th->tid);
> +	}
> +}
> +

I think you should combine the above function with
thread__join_map_groups, and I think that the method belongs to the
'machine' class, see below for further comments on this...

>  static struct thread *__machine__findnew_thread(struct machine *machine,
>  						pid_t pid, pid_t tid,
>  						bool create)
> @@ -285,10 +296,10 @@ static struct thread *__machine__findnew_thread(struct machine *machine,
>  	 * so most of the time we dont have to look up
>  	 * the full rbtree:
>  	 */
> -	if (machine->last_match && machine->last_match->tid == tid) {
> -		if (pid != -1 && pid != machine->last_match->pid_)
> -			machine->last_match->pid_ = pid;
> -		return machine->last_match;
> +	th = machine->last_match;
> +	if (th && th->tid == tid) {
> +		machine__update_thread_pid(machine, th, pid);
> +		return th;
>  	}
>  
>  	while (*p != NULL) {
> @@ -297,8 +308,7 @@ static struct thread *__machine__findnew_thread(struct machine *machine,
>  
>  		if (th->tid == tid) {
>  			machine->last_match = th;
> -			if (pid != -1 && pid != th->pid_)
> -				th->pid_ = pid;
> +			machine__update_thread_pid(machine, th, pid);
>  			return th;
>  		}
>  
> diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
> index 25c571f..7af1480 100644
> --- a/tools/perf/util/map.c
> +++ b/tools/perf/util/map.c
> @@ -454,6 +454,20 @@ void map_groups__exit(struct map_groups *mg)
>  	}
>  }
>  
> +bool map_groups__empty(struct map_groups *mg)
> +{
> +	int i;
> +
> +	for (i = 0; i < MAP__NR_TYPES; ++i) {
> +		if (maps__first(&mg->maps[i]))
> +			return false;
> +		if (!list_empty(&mg->removed_maps[i]))
> +			return false;
> +	}
> +
> +	return true;
> +}
> +
>  struct map_groups *map_groups__new(void)
>  {
>  	struct map_groups *mg = malloc(sizeof(*mg));
> diff --git a/tools/perf/util/map.h b/tools/perf/util/map.h
> index 7758c72..5806a90 100644
> --- a/tools/perf/util/map.h
> +++ b/tools/perf/util/map.h
> @@ -66,6 +66,7 @@ struct map_groups {
>  
>  struct map_groups *map_groups__new(void);
>  void map_groups__delete(struct map_groups *mg);
> +bool map_groups__empty(struct map_groups *mg);
>  
>  static inline struct map_groups *map_groups__get(struct map_groups *mg)
>  {
> diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
> index 7a32f44..ca94295 100644
> --- a/tools/perf/util/thread.c
> +++ b/tools/perf/util/thread.c
> @@ -24,6 +24,41 @@ int thread__init_map_groups(struct thread *thread, struct machine *machine)
>  	return thread->mg ? 0 : -1;
>  }
>  
> +int thread__join_map_groups(struct thread *thread, struct machine *machine)
> +{
> +	struct thread *leader;
> +	pid_t pid = thread->pid_;
> +
> +	if (pid == thread->tid)
> +		return 0;
> +
> +	leader = machine__findnew_thread(machine, pid, pid);
> +	if (!leader)
> +		return -ENOMEM;
> +
> +	if (!leader->mg)
> +		leader->mg = map_groups__new();
> +
> +	if (!leader->mg)
> +		return -ENOMEM;
> +
> +	if (thread->mg) {
> +		/*
> +		 * Maps are created from MMAP events which provide the pid and
> +		 * tid.  Consequently there never should be any maps on a thread
> +		 * with an unknown pid.  Just print an error if there are.
> +		 */
> +		if (!map_groups__empty(thread->mg))
> +			pr_err("Discarding thread maps for %d:%d\n",
> +			       thread->pid_, thread->tid);

Because there is nothing in this function (thread__join_map_groups),
checking if it is operating on a thread that has an unknown pid.

So, please consider merging this and its sole caller,
machine__update_thread_pid, so that the test is in the same function as
the assumption that it is operating on a thread with an unknown pid.

Continuing to look at the other patches...

> +		map_groups__delete(thread->mg);
> +	}
> +
> +	thread->mg = map_groups__get(leader->mg);
> +
> +	return 0;
> +}
> +
>  struct thread *thread__new(pid_t pid, pid_t tid)
>  {
>  	char *comm_str;
> diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
> index 3c0c272..9de0629 100644
> --- a/tools/perf/util/thread.h
> +++ b/tools/perf/util/thread.h
> @@ -31,6 +31,7 @@ struct comm;
>  
>  struct thread *thread__new(pid_t pid, pid_t tid);
>  int thread__init_map_groups(struct thread *thread, struct machine *machine);
> +int thread__join_map_groups(struct thread *thread, struct machine *machine);
>  void thread__delete(struct thread *thread);
>  static inline void thread__exited(struct thread *thread)
>  {
> -- 
> 1.8.3.2
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