[PATCH 2/2] perf tools: Fix another seg fault using Intel PT

From: Adrian Hunter
Date: Tue Jan 26 2016 - 07:08:56 EST

Fix segmentation fault using:

perf record -e intel_pt//u uname
perf script

Back trace:

0 __list_del (next=0x1880710, prev=0x0) at /home/ahunter/git/linux/tools/include/linux/list.h:89
1 __list_del_entry (entry=0x1880710) at /home/ahunter/git/linux/tools/include/linux/list.h:101
2 list_del_init (entry=0x1880710) at /home/ahunter/git/linux/tools/include/linux/list.h:144
3 thread__put (thread=0x1880710) at util/thread.c:104
4 0x00000000004fd699 in intel_pt_free (session=0x186fb90) at util/intel-pt.c:1747
5 0x00000000004c23cc in auxtrace__free (session=0x186fb90) at util/auxtrace.h:511
6 perf_session__delete (session=session@entry=0x186fb90) at util/session.c:181
7 0x0000000000443398 in cmd_script (argc=<optimized out>, argv=<optimized out>, prefix=<optimized out>) at builtin-script.c:2232
8 0x000000000047cbd3 in run_builtin (p=p@entry=0x7cf3a8 <commands+360>, argc=argc@entry=1, argv=argv@entry=0x7fffffffe210) at perf.c:390
9 0x00000000004216a7 in handle_internal_command (argv=0x7fffffffe210, argc=1) at perf.c:451
10 run_argv (argv=0x7fffffffdf90, argcp=0x7fffffffdf9c) at perf.c:495
11 main (argc=1, argv=0x7fffffffe210) at perf.c:618

The seg fault happens when Intel PT "puts" a "struct thread"
that has been created as a placeholder for unknown threads.
thread__put() assumes that a thread's list node can be deleted,
which is not true in the case above because of:

commit fdce6a4edaad ("perf tools: Remove redundant initialization of thread linkage members")

which removed the list node initialization.

Expecting the list node to be re-initialized whenever removing a
thread from an rb-tree seems fragile, so fix by taking the list
node out of union, so that list_del_init() can be used on it with

Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
tools/perf/util/thread.c | 2 ++
tools/perf/util/thread.h | 6 ++----
2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
index dfd00c6dad6e..e8af90c1e66d 100644
--- a/tools/perf/util/thread.c
+++ b/tools/perf/util/thread.c
@@ -56,6 +56,7 @@ struct thread *thread__new(pid_t pid, pid_t tid)

list_add(&comm->list, &thread->comm_list);
atomic_set(&thread->refcnt, 1);
+ INIT_LIST_HEAD(&thread->node);

@@ -71,6 +72,7 @@ void thread__delete(struct thread *thread)
struct comm *comm, *tmp;

+ BUG_ON(!list_empty(&thread->node));


diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
index a0ac0317affb..6430b168a62f 100644
--- a/tools/perf/util/thread.h
+++ b/tools/perf/util/thread.h
@@ -13,10 +13,8 @@
struct thread_stack;

struct thread {
- union {
- struct rb_node rb_node;
- struct list_head node;
- };
+ struct rb_node rb_node;
+ struct list_head node;
struct map_groups *mg;
pid_t pid_; /* Not all tools update this */
pid_t tid;