On 01/02/16 05:21, Wang Nan wrote: > In error processing path of intel_pt_process_auxtrace_info() it calls > thread__zput() to clean and free pt->unknown_thread which is created by > thread__new(). However, when error raise, a segfault happen: > > # 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 during > creating, inserted into machine->threads rbtree uses rb_node, move to > machine->dead_threads using list_head, clean by thread__put: > list_del_init(&thread->node).
I sent a different patch for this: http://marc.info/?l=linux-kernel&m=145381014011697 > > In the above command, it clean a thread before adding it into list, > causes the above segfault. > > This patch gives a fake list_head and link the thread into it before > calling thread__zput(), get rid of the 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 <zt...@vt.edu> > Signed-off-by: Wang Nan <wangn...@huawei.com> > Cc: Adrian Hunter <adrian.hun...@intel.com> > Cc: Arnaldo Carvalho de Melo <a...@redhat.com> > Cc: Josh Poimboeuf <jpoim...@redhat.com> > --- > tools/perf/util/intel-pt.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c > index 81a2eb7..e2add63 100644 > --- a/tools/perf/util/intel-pt.c > +++ b/tools/perf/util/intel-pt.c > @@ -2013,6 +2013,7 @@ int intel_pt_process_auxtrace_info(union perf_event > *event, > struct auxtrace_info_event *auxtrace_info = &event->auxtrace_info; > size_t min_sz = sizeof(u64) * INTEL_PT_PER_CPU_MMAPS; > struct intel_pt *pt; > + struct list_head dead_thread; > int err; > > if (auxtrace_info->header.size < sizeof(struct auxtrace_info_event) + > @@ -2153,6 +2154,9 @@ int intel_pt_process_auxtrace_info(union perf_event > *event, > return 0; > > err_delete_thread: > + RB_CLEAR_NODE(&pt->unknown_thread->rb_node); > + INIT_LIST_HEAD(&dead_thread); > + list_add(&pt->unknown_thread->node, &dead_thread); > thread__zput(pt->unknown_thread); > err_free_queues: > intel_pt_log_disable(); >