[PATCH 1/1] perf tools: Flush maps on COMM events

[Arnaldo Carvalho de Melo]

From: David S. Miller <davem@xxxxxxxxxxxxx>

Even though we don't register the counters until the child is right about to
exec(), we're still going to get at least a few events while the fork()'d child
is still executing 'perf' and in particular we're going to get the MMAP events.

We can't distinguish the ones in the newly executed process because the PID
will be the same.

One way to solve this would be to have a PERF_RECORD_EXEC event, and when this
is seen 'perf' can flush it's map cache.  We can't use PERF_RECORD_COMM since
that's generated by other things, not just exec().

Actually, thinking about it some more, using PERF_RECORD_COMM might be a good
enough approximation.

Cc: FrÃdÃric Weisbecker <fweisbec@xxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/thread.c |   34 ++++++++++++++++++++++++++++++----
 1 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
index c090654..21b9216 100644
--- a/tools/perf/util/thread.c
+++ b/tools/perf/util/thread.c
@@ -31,15 +31,41 @@ static struct thread *thread__new(pid_t pid)
 	return self;
 }
 
+static void map_groups__flush(struct map_groups *self)
+{
+	int type;
+
+	for (type = 0; type < MAP__NR_TYPES; type++) {
+		struct rb_root *root = &self->maps[type];
+		struct rb_node *next = rb_first(root);
+
+		while (next) {
+			struct map *pos = rb_entry(next, struct map, rb_node);
+			next = rb_next(&pos->rb_node);
+			rb_erase(&pos->rb_node, root);
+			/*
+			 * We may have references to this map, for
+			 * instance in some hist_entry instances, so
+			 * just move them to a separate list.
+			 */
+			list_add_tail(&pos->node, &self->removed_maps[pos->type]);
+		}
+	}
+}
+
 int thread__set_comm(struct thread *self, const char *comm)
 {
+	int err;
+
 	if (self->comm)
 		free(self->comm);
 	self->comm = strdup(comm);
-	if (self->comm == NULL)
-		return -ENOMEM;
-	self->comm_set = true;
-	return 0;
+	err = self->comm == NULL ? -ENOMEM : 0;
+	if (!err) {
+		self->comm_set = true;
+		map_groups__flush(&self->mg);
+	}
+	return err;
 }
 
 int thread__comm_len(struct thread *self)
-- 
1.5.5.1

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