linux-kernel - [PATCH 3/3] perf: fix synthesizing mmaps for threads

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Message-Id: <1393386227-149412-4-git-send-email-dzickus@redhat.com>
Date:	Tue, 25 Feb 2014 22:43:47 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	acme@...stprotocols.net, jolsa@...hat.com, eranian@...gle.com,
	Don Zickus <dzickus@...hat.com>
Subject: [PATCH 3/3] perf: fix synthesizing mmaps for threads

Currently if a process creates a bunch of threads using pthread_create
and then perf is run in system_wide mode, the mmaps for those threads
are not captured with a synthesized mmap event.

The reason is those threads are not visible when walking the /proc/
directory looking for /proc/<pid>/maps files.  Instead they are discovered
using the /proc/<pid>/tasks file (which the synthesized comm event uses).

This causes problems when a program is trying to map a data address to a
tid.  Because the tid has no maps, the event is dropped.  Changing the program
to look up using the pid instead of the tid, finds the correct maps but creates
ugly hacks in the program to carry the correct tid around.

Fix this by synthesizing mmap events for each tid found in the /proc/<pid>/tasks
file.

This may not be entirely clean but it seems to work.

Signed-off-by: Don Zickus <dzickus@...hat.com>
---
 tools/perf/util/event.c   | 15 +++++++++++----
 tools/perf/util/machine.c |  4 ++--
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 086c7c8..09c53bb 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -93,10 +93,13 @@ static pid_t perf_event__get_comm_tgid(pid_t pid, char *comm, size_t len)
 }
 
 static pid_t perf_event__synthesize_comm(struct perf_tool *tool,
-					 union perf_event *event, pid_t pid,
+					 union perf_event *event,
+					 union perf_event *mmap_event,
+					 pid_t pid,
 					 int full,
 					 perf_event__handler_t process,
-					 struct machine *machine)
+					 struct machine *machine,
+					 bool mmap_data)
 {
 	char filename[PATH_MAX];
 	size_t size;
@@ -168,6 +171,10 @@ static pid_t perf_event__synthesize_comm(struct perf_tool *tool,
 			tgid = -1;
 			break;
 		}
+
+		/* process the thread's maps too */
+		perf_event__synthesize_mmap_events(tool, mmap_event, pid, tgid,
+						  process, machine, mmap_data);
 	}
 
 	closedir(tasks);
@@ -331,8 +338,8 @@ static int __event__synthesize_thread(union perf_event *comm_event,
 				      struct perf_tool *tool,
 				      struct machine *machine, bool mmap_data)
 {
-	pid_t tgid = perf_event__synthesize_comm(tool, comm_event, pid, full,
-						 process, machine);
+	pid_t tgid = perf_event__synthesize_comm(tool, comm_event, mmap_event, pid,
+						 full, process, machine, mmap_data);
 	if (tgid == -1)
 		return -1;
 	return perf_event__synthesize_mmap_events(tool, mmap_event, pid, tgid,
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 813e94e..eb26544 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1026,7 +1026,7 @@ int machine__process_mmap2_event(struct machine *machine,
 	}
 
 	thread = machine__findnew_thread(machine, event->mmap2.pid,
-					event->mmap2.pid);
+					event->mmap2.tid);
 	if (thread == NULL)
 		goto out_problem;
 
@@ -1074,7 +1074,7 @@ int machine__process_mmap_event(struct machine *machine, union perf_event *event
 	}
 
 	thread = machine__findnew_thread(machine, event->mmap.pid,
-					 event->mmap.pid);
+					 event->mmap.tid);
 	if (thread == NULL)
 		goto out_problem;
 
-- 
1.7.11.7

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