See http://www.infradead.org/rpr.html
From: Adrian Hunter <[email protected]> intel_pt_process_auxtrace_info() creates a pt->unknown_thread thread that eventually needs to be freed by the last thread__put() on it, when its refcount hits zero, which may happen in intel_pt_process_auxtrace_info() error handling path and triggers the following segfault, which would happen as well at intel_pt_free, when tools using this intel_pt codebase frees up resources: # perf record -I -e intel_pt/tsc=1,noretcomp=1/u /bin/ls 0 a anaconda-ks.cfg bin perf.data perf.data.old perf-f23-bringup.todo [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.217 MB perf.data ] # # perf script -F event,comm,pid,tid,time,addr,ip,sym,dso,iregs Samples for 'instructions:u' event do not have IREGS attribute set. Cannot print 'iregs' field. intel_pt_synth_events: failed to synthesize 'instructions' event type Segmentation fault (core dumped) # The problem is: there's a union in 'struct thread' combines a list_head and a rb_node. The standard life cycle of a thread is: init rb_node in the constructor, insert it into machine->threads rbtree using rb_node, move it to machine->dead_threads using list_head, clean in the last thread__put: list_del_init(&thread->node). In the above command, it clean a thread before adding it into list, causes the above segfault. Since pt->unknown_thread will never live in an rbtree, initialize its list node so that when list_del_init() is done on it we don't segfault. After this patch: # perf script -F event,comm,pid,tid,time,addr,ip,sym,dso,iregs Samples for 'instructions:u' event do not have IREGS attribute set. Cannot print 'iregs' field. intel_pt_synth_events: failed to synthesize 'instructions' event type 0x248 [0x88]: failed to process type: 70 # Reported-by: Tong Zhang <[email protected]> Reported-by: Wang Nan <[email protected]> Signed-off-by: Adrian Hunter <[email protected]> Tested-by: Arnaldo Carvalho de Melo <[email protected]> Cc: Josh Poimboeuf <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Arnaldo Carvalho de Melo <[email protected]> --- tools/perf/util/intel-pt.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c index 81a2eb77ba7f..05d815851be1 100644 --- a/tools/perf/util/intel-pt.c +++ b/tools/perf/util/intel-pt.c @@ -2068,6 +2068,15 @@ int intel_pt_process_auxtrace_info(union perf_event *event, err = -ENOMEM; goto err_free_queues; } + + /* + * Since this thread will not be kept in any rbtree not in a + * list, initialize its list node so that at thread__put() the + * current thread lifetime assuption is kept and we don't segfault + * at list_del_init(). + */ + INIT_LIST_HEAD(&pt->unknown_thread->node); + err = thread__set_comm(pt->unknown_thread, "unknown", 0); if (err) goto err_delete_thread; -- 2.5.0
