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Subject: Re: [PATCH] trace: circular dependency for trace_types_lock and
 event_mutex
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     mingo@redhat.com, linux-kernel@vger.kernel.org,
        kaushalk@codeaurora.org
References: <0101016ecc80a1fa-27cc3e87-c16d-4cd6-b3c6-9c893010fdef-000000@us-west-2.amazonses.com>
 <20191203112730.77b334f6@gandalf.local.home>
From:   Prateek Sood <prsood@codeaurora.org>
Message-ID: <0101016ecf398cfb-7361e722-7792-423a-85cf-7dd2fe048e9d-000000@us-west-2.amazonses.com>
Date:   Wed, 4 Dec 2019 04:44:45 +0000
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On 12/3/19 9:57 PM, Steven Rostedt wrote:
> 
> Hi Prateek,
> 
> Thanks for the patch. Note, I think a better subject is:
> 
>  tracing: Fix lock inversion caused by trace_event_enable_tgid_record()
Ok, I will update and send with updated subject.

> 
> 
> On Tue, 3 Dec 2019 16:03:32 +0000
> Prateek Sood <prsood@codeaurora.org> wrote:
> 
>>        Task T2                             Task T3
>> trace_options_core_write()            subsystem_open()
>>
>>  mutex_lock(trace_types_lock)           mutex_lock(event_mutex)
>>
>>  set_tracer_flag()
>>
>>    trace_event_enable_tgid_record()       mutex_lock(trace_types_lock)
>>
>>     mutex_lock(event_mutex)
>>
>> This gives a circular dependency deadlock between trace_types_lock and
>> event_mutex. To fix this invert the usage of trace_types_lock and event_mutex
>> in trace_options_core_write(). This keeps the sequence of lock usage consistent.
>>
>> Change-Id: I3752a77c59555852c2241f7775ec4a1960c15c15
> 
> What's this Change-Id? Something internal?

Apologies, this is something internal which I missed to remove

> 
> I'll be adding:
> 
>  Link: http://lkml.kernel.org/r/0101016ecc80a1fa-27cc3e87-c16d-4cd6-b3c6-9c893010fdef-000000@us-west-2.amazonses.com
> 
> I'll test this out, and probably even add a stable tag.

Ok

Thanks for reviewing it!!

> 
> -- Steve
> 
> 
> 
>> Signed-off-by: Prateek Sood <prsood@codeaurora.org>
>> ---
>>  kernel/trace/trace.c              | 6 ++++++
>>  kernel/trace/trace_events.c       | 8 ++++----
>>  kernel/trace/trace_irqsoff.c      | 4 ++++
>>  kernel/trace/trace_sched_wakeup.c | 4 ++++
>>  4 files changed, 18 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index 6a0ee91..2c09aa1 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -4590,6 +4590,8 @@ int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set)
>>  
>>  int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled)
>>  {
>> +	lockdep_assert_held(&event_mutex);
>> +
>>  	/* do nothing if flag is already set */
>>  	if (!!(tr->trace_flags & mask) == !!enabled)
>>  		return 0;
>> @@ -4657,6 +4659,7 @@ static int trace_set_options(struct trace_array *tr, char *option)
>>  
>>  	cmp += len;
>>  
>> +	mutex_lock(&event_mutex);
>>  	mutex_lock(&trace_types_lock);
>>  
>>  	ret = match_string(trace_options, -1, cmp);
>> @@ -4667,6 +4670,7 @@ static int trace_set_options(struct trace_array *tr, char *option)
>>  		ret = set_tracer_flag(tr, 1 << ret, !neg);
>>  
>>  	mutex_unlock(&trace_types_lock);
>> +	mutex_unlock(&event_mutex);
>>  
>>  	/*
>>  	 * If the first trailing whitespace is replaced with '\0' by strstrip,
>> @@ -7972,9 +7976,11 @@ static void get_tr_index(void *data, struct trace_array **ptr,
>>  	if (val != 0 && val != 1)
>>  		return -EINVAL;
>>  
>> +	mutex_lock(&event_mutex);
>>  	mutex_lock(&trace_types_lock);
>>  	ret = set_tracer_flag(tr, 1 << index, val);
>>  	mutex_unlock(&trace_types_lock);
>> +	mutex_unlock(&event_mutex);
>>  
>>  	if (ret < 0)
>>  		return ret;
>> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
>> index fba87d1..995061b 100644
>> --- a/kernel/trace/trace_events.c
>> +++ b/kernel/trace/trace_events.c
>> @@ -320,7 +320,8 @@ void trace_event_enable_cmd_record(bool enable)
>>  	struct trace_event_file *file;
>>  	struct trace_array *tr;
>>  
>> -	mutex_lock(&event_mutex);
>> +	lockdep_assert_held(&event_mutex);
>> +
>>  	do_for_each_event_file(tr, file) {
>>  
>>  		if (!(file->flags & EVENT_FILE_FL_ENABLED))
>> @@ -334,7 +335,6 @@ void trace_event_enable_cmd_record(bool enable)
>>  			clear_bit(EVENT_FILE_FL_RECORDED_CMD_BIT, &file->flags);
>>  		}
>>  	} while_for_each_event_file();
>> -	mutex_unlock(&event_mutex);
>>  }
>>  
>>  void trace_event_enable_tgid_record(bool enable)
>> @@ -342,7 +342,8 @@ void trace_event_enable_tgid_record(bool enable)
>>  	struct trace_event_file *file;
>>  	struct trace_array *tr;
>>  
>> -	mutex_lock(&event_mutex);
>> +	lockdep_assert_held(&event_mutex);
>> +
>>  	do_for_each_event_file(tr, file) {
>>  		if (!(file->flags & EVENT_FILE_FL_ENABLED))
>>  			continue;
>> @@ -356,7 +357,6 @@ void trace_event_enable_tgid_record(bool enable)
>>  				  &file->flags);
>>  		}
>>  	} while_for_each_event_file();
>> -	mutex_unlock(&event_mutex);
>>  }
>>  
>>  static int __ftrace_event_enable_disable(struct trace_event_file *file,
>> diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
>> index a745b0c..887cdb5 100644
>> --- a/kernel/trace/trace_irqsoff.c
>> +++ b/kernel/trace/trace_irqsoff.c
>> @@ -560,8 +560,10 @@ static int __irqsoff_tracer_init(struct trace_array *tr)
>>  	save_flags = tr->trace_flags;
>>  
>>  	/* non overwrite screws up the latency tracers */
>> +	mutex_lock(&event_mutex);
>>  	set_tracer_flag(tr, TRACE_ITER_OVERWRITE, 1);
>>  	set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, 1);
>> +	mutex_unlock(&event_mutex);
>>  
>>  	tr->max_latency = 0;
>>  	irqsoff_trace = tr;
>> @@ -586,8 +588,10 @@ static void __irqsoff_tracer_reset(struct trace_array *tr)
>>  
>>  	stop_irqsoff_tracer(tr, is_graph(tr));
>>  
>> +	mutex_lock(&event_mutex);
>>  	set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, lat_flag);
>>  	set_tracer_flag(tr, TRACE_ITER_OVERWRITE, overwrite_flag);
>> +	mutex_unlock(&event_mutex);
>>  	ftrace_reset_array_ops(tr);
>>  
>>  	irqsoff_busy = false;
>> diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
>> index 5e43b96..0bc67d1 100644
>> --- a/kernel/trace/trace_sched_wakeup.c
>> +++ b/kernel/trace/trace_sched_wakeup.c
>> @@ -671,8 +671,10 @@ static int __wakeup_tracer_init(struct trace_array *tr)
>>  	save_flags = tr->trace_flags;
>>  
>>  	/* non overwrite screws up the latency tracers */
>> +	mutex_lock(&event_mutex);
>>  	set_tracer_flag(tr, TRACE_ITER_OVERWRITE, 1);
>>  	set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, 1);
>> +	mutex_unlock(&event_mutex);
>>  
>>  	tr->max_latency = 0;
>>  	wakeup_trace = tr;
>> @@ -722,8 +724,10 @@ static void wakeup_tracer_reset(struct trace_array *tr)
>>  	/* make sure we put back any tasks we are tracing */
>>  	wakeup_reset(tr);
>>  
>> +	mutex_lock(&event_mutex);
>>  	set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, lat_flag);
>>  	set_tracer_flag(tr, TRACE_ITER_OVERWRITE, overwrite_flag);
>> +	mutex_unlock(&event_mutex);
>>  	ftrace_reset_array_ops(tr);
>>  	wakeup_busy = false;
>>  }
> 


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