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

Message ID 1454346792-24419-3-git-send-email-acme@kernel.org
State New
Headers show

Commit Message

Arnaldo Carvalho de Melo Feb. 1, 2016, 5:13 p.m.
From: Wang Nan <wangnan0@huawei.com>


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 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 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).

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 <ztong@vt.edu>
Signed-off-by: Wang Nan <wangnan0@huawei.com>

Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Cc: Adrian Hunter <adrian.hunter@intel.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 | 4 ++++
 1 file changed, 4 insertions(+)

-- 
2.5.0

Comments

Wang Nan Feb. 3, 2016, 2:06 a.m. | #1
On 2016/2/2 23:52, 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?


I didn't really understand the lifecycle of unknown_thread, and though
it would go to an rbtree in normal path. I think the patch you posted
is good.

Thank you.

>  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;

Patch

diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c
index 81a2eb77ba7f..e2add6376fec 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();