Re: [PATCH 2/2] perf tools: Fix fault in error patch of intel_pt_process_auxtrace_info()

[Adrian Hunter]

On 2/02/2016 5:52 p.m., Arnaldo Carvalho de Melo wrote:
> Em Tue, Feb 02, 2016 at 12:24:19PM +0200, Adrian Hunter escreveu:
> > This patch does not fix the problem because the thread__zput() will still
> > segfault later if the error path is not taken.
> >
> > Sorry, I didn't look closely at this patch because I was not expecting it
> > to be taken because of the fix I had already sent:
> >
> > 	http://marc.info/?l=linux-kernel&m=145431692623940
> >
> > However if you want to keep the struct thread rbtree / list union, the
> > simple fix would be to reinstate the list initialization in this particular
> > case i.e.:
>
> So, can I go with the following patch+description+authorship?

Fine by me.  Thank you!

>  From 3a4acda1ecbd290973de08250d7dcdfaf5b2fe0f Mon Sep 17 00:00:00 2001
> From: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Date: Mon, 1 Feb 2016 03:21:04 +0000
> Subject: [PATCH 1/1] 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@xxxxxx>
> Reported-by: Wang Nan <wangnan0@xxxxxxxxxx>
> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Tested-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Link: http://lkml.kernel.org/r/1454296865-19749-1-git-send-email-wangnan0@xxxxxxxxxx
> Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> ---
>   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;