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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Tue, Feb 02, 2016 at 12:52:25PM -0300, Arnaldo Carvalho de Melo escreveu:
> 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?

BTW, I just noticed it while testing some unrelated patch (Jiri's hpp
hists stuff) that with a perf.data file with intel pt data, I get this
at the end of a TUI session, i.e. the segfault at tool exit:


Available samples
0 intel_pt/tsc=1,noretcomp=1/u                                                                                                                                              ◆
29 sched:sched_switch                                                                                                                                                       ▒
0 dummy:u                                                                                                                                                                   ▒
6 instructions:u                                                                                                                                                            ▒
0 transactions                                                                                                                                                              ▒
                                                                                                                                                                            Program received signal SIGSEGV, Segmentation fault.                                                                                                                         ▒
                                                   0x00000000004ec5c5 in __write_once_size (size=8, res=0x7fffffffc2e0, p=0x0) at /home/acme/git/linux/tools/include/linux/compiler.h:82                                                                                                                                                                 ▒
82              case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break;                                                                                      ▒
Missing separate debuginfos, use: dnf debuginfo-install audit-libs-2.4.5-1.fc23.x86_64 bzip2-libs-1.0.6-19.fc23.x86_64 elfutils-libelf-0.165-2.fc23.x86_64 elfutils-libs-0.165-2.fc23.x86_64 libunwind-1.1-10.fc23.x86_64 nss-softokn-freebl-3.21.0-1.1.fc23.x86_64 numactl-libs-2.0.10-3.fc23.x86_64 perl-libs-5.22.1-350.fc23.x86_64 python-libs-2.7.10-8.fc23.x86_64 slang-2.3.0-4.fc23.x86_64 xz-libs-5.2.1-3.fc23.x86_64 zlib-1.2.8-9.fc23.x86_64                                                                                ▒
(gdb) bt                                                                                                                                                                    ▒
#0  0x00000000004ec5c5 in __write_once_size (size=8, res=0x7fffffffc2e0, p=0x0) at /home/acme/git/linux/tools/include/linux/compiler.h:82                                   ▒
#1  __list_del (prev=0x0, next=0x1a2e970) at /home/acme/git/linux/tools/include/linux/list.h:89                                                                             ▒
#2  0x00000000004ec631 in __list_del_entry (entry=0x1a2e970) at /home/acme/git/linux/tools/include/linux/list.h:101                                                         ▒
#3  0x00000000004ec6d2 in list_del_init (entry=0x1a2e970) at /home/acme/git/linux/tools/include/linux/list.h:144                                                            ▒
#4  0x00000000004ecd2a in thread__put (thread=0x1a2e970) at util/thread.c:104                                                                                               ▒
#5  0x000000000052de51 in intel_pt_free (session=0x19a3b90) at util/intel-pt.c:1747                                                                                         ▒
#6  0x00000000004e4e3d in auxtrace__free (session=0x19a3b90) at util/auxtrace.h:513                                                                                         ▒
#7  0x00000000004e5603 in perf_session__delete (session=0x19a3b90) at util/session.c:181                                                                                    ▒
#8  0x00000000004363f3 in cmd_report (argc=0, argv=0x7fffffffdeb0, prefix=0x0) at builtin-report.c:984                                                                      ▒
#9  0x000000000049bea3 in run_builtin (p=0x8fa2c0 <commands+192>, argc=1, argv=0x7fffffffdeb0) at perf.c:390                                                                ▒
#10 0x000000000049c10b in handle_internal_command (argc=1, argv=0x7fffffffdeb0) at perf.c:451                                                                               ▒
#11 0x000000000049c259 in run_argv (argcp=0x7fffffffdd0c, argv=0x7fffffffdd00) at perf.c:495                                                                                ▒
#12 0x000000000049c5eb in main (argc=1, argv=0x7fffffffdeb0) at perf.c:618                                                                                                  ▒
(gdb) 
 
> From 3a4acda1ecbd290973de08250d7dcdfaf5b2fe0f Mon Sep 17 00:00:00 2001
> From: Adrian Hunter <adrian.hunter@intel.com>
> 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@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>
> ---
>  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
>