perf session: Remove threads from tree on PERF_RECORD_EXIT

Move them to a session->dead_threads list just like we do with maps that
are replaced, because we may have hist_entries pointing to them.

This fixes a bug when inserting maps for a new thread that reused the
TID, mixing maps for two different threads, causing an endless loop.

The code for insering maps should be made more robust but for .35 this
is the minimalistic patch.
Reported-by: Ingo Molnar <mingo@elte.hu>
Cc: David S. Miller <davem@davemloft.net>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/event.c

@@ -538,8 +538,10 @@ int event__process_task(event_t *self, struct perf_session *session)
 	dump_printf("(%d:%d):(%d:%d)\n", self->fork.pid, self->fork.tid,
 		    self->fork.ppid, self->fork.ptid);
 
-	if (self->header.type == PERF_RECORD_EXIT)
+	if (self->header.type == PERF_RECORD_EXIT) {
+		perf_session__remove_thread(session, thread);
 		return 0;
+	}
 
 	if (thread == NULL || parent == NULL ||
 	    thread__fork(thread, parent) < 0) {

tools/perf/util/session.c

@@ -90,6 +90,7 @@ struct perf_session *perf_session__new(const char *filename, int mode, bool forc
 
 	memcpy(self->filename, filename, len);
 	self->threads = RB_ROOT;
+	INIT_LIST_HEAD(&self->dead_threads);
 	self->hists_tree = RB_ROOT;
 	self->last_match = NULL;
 	self->mmap_window = 32;
@@ -131,6 +132,16 @@ void perf_session__delete(struct perf_session *self)
 	free(self);
 }
 
+void perf_session__remove_thread(struct perf_session *self, struct thread *th)
+{
+	rb_erase(&th->rb_node, &self->threads);
+	/*
+	 * We may have references to this thread, for instance in some hist_entry
+	 * instances, so just move them to a separate list.
+	 */
+	list_add_tail(&th->node, &self->dead_threads);
+}
+
 static bool symbol__match_parent_regex(struct symbol *sym)
 {
 	if (sym->name && !regexec(&parent_regex, sym->name, 0, NULL, 0))

tools/perf/util/session.h

@@ -26,6 +26,7 @@ struct perf_session {
 	unsigned long		size;
 	unsigned long		mmap_window;
 	struct rb_root		threads;
+	struct list_head	dead_threads;
 	struct thread		*last_match;
 	struct machine		host_machine;
 	struct rb_root		machines;
@@ -99,6 +100,7 @@ int perf_session__create_kernel_maps(struct perf_session *self);
 
 int do_read(int fd, void *buf, size_t size);
 void perf_session__update_sample_type(struct perf_session *self);
+void perf_session__remove_thread(struct perf_session *self, struct thread *th);
 
 static inline
 struct machine *perf_session__find_host_machine(struct perf_session *self)

tools/perf/util/thread.h

@@ -6,7 +6,10 @@
 #include "symbol.h"
 
 struct thread {
+	union {
 		struct rb_node	 rb_node;
+		struct list_head node;
+	};
 	struct map_groups	mg;
 	pid_t			pid;
 	char			shortname[3];