perf tools: Fix thread lifetime related segfaut in intel_pt
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 <ztong@vt.edu> Reported-by: Wang Nan <wangnan0@huawei.com> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Link: http://lkml.kernel.org/r/1454296865-19749-1-git-send-email-wangnan0@huawei.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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@ -2068,6 +2068,15 @@ int intel_pt_process_auxtrace_info(union perf_event *event,
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err = -ENOMEM;
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goto err_free_queues;
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}
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/*
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* Since this thread will not be kept in any rbtree not in a
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* list, initialize its list node so that at thread__put() the
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* current thread lifetime assuption is kept and we don't segfault
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* at list_del_init().
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*/
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INIT_LIST_HEAD(&pt->unknown_thread->node);
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err = thread__set_comm(pt->unknown_thread, "unknown", 0);
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if (err)
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goto err_delete_thread;
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