linux-kernel - Re: [PATCH 2/2] perf tools: Fix fault in error patch of intel_pt_process_auxtrace

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Date:	Tue, 2 Feb 2016 11:08:06 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Wang Nan <wangnan0@...wei.co>, Ingo Molnar <mingo@...nel.org>,
	linux-kernel@...r.kernel.org, Wang Nan <wangnan0@...wei.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 2/2] perf tools: Fix fault in error patch of
 intel_pt_process_auxtrace_info()

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.:

Right, so it keeps the existing thread lifetime assumptions both in the
error path, as Wang did, and in the normal pt->unknown_thread end of
life at intel_pt_free(), I'm replacing the patch...

- Arnaldo
 
> 
> diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c
> index 81a2eb7..18245b8 100644
> --- a/tools/perf/util/intel-pt.c
> +++ b/tools/perf/util/intel-pt.c
> @@ -2068,6 +2068,7 @@ int intel_pt_process_auxtrace_info(union perf_event
>                 err = -ENOMEM;
>                 goto err_free_queues;
>         }
> +       INIT_LIST_HEAD(&pt->unknown_thread->node);
>         err = thread__set_comm(pt->unknown_thread, "unknown", 0);
>         if (err)
>                 goto err_delete_thread;
> 
> 
> 
> On 01/02/16 19:13, Arnaldo Carvalho de Melo wrote:
> > From: Wang Nan <wangnan0@...wei.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@...edu>
> > Signed-off-by: Wang Nan <wangnan0@...wei.com>
> > Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> > Cc: Adrian Hunter <adrian.hunter@...el.com>
> > Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> > Link: http://lkml.kernel.org/r/1454296865-19749-1-git-send-email-wangnan0@huawei.com
> > Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.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 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();
> >