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SubjectRe: [PATCH 3/3] tracing: Add 2 new funcs. for kernel access to Ftrace instances.
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Hi Steven,

Thanks for taking the time to review. Please find my comments inline.

On 6/8/19 2:51 PM, Steven Rostedt wrote:
> On Tue, 4 Jun 2019 17:42:05 -0700
> Divya Indi <divya.indi@oracle.com> wrote:
>
>> Adding 2 new functions -
>> 1) trace_array_lookup : Look up and return a trace array, given its
>> name.
>> 2) trace_array_set_clr_event : Enable/disable event recording to the
>> given trace array.
>>
>> Signed-off-by: Divya Indi <divya.indi@oracle.com>
>> ---
>> include/linux/trace_events.h | 3 +++
>> kernel/trace/trace.c | 11 +++++++++++
>> kernel/trace/trace_events.c | 22 ++++++++++++++++++++++
>> 3 files changed, 36 insertions(+)
>>
>> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
>> index d7b7d85..0cc99a8 100644
>> --- a/include/linux/trace_events.h
>> +++ b/include/linux/trace_events.h
>> @@ -545,7 +545,10 @@ int trace_array_printk(struct trace_array *tr, unsigned long ip,
>> struct trace_array *trace_array_create(const char *name);
>> int trace_array_destroy(struct trace_array *tr);
>> int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set);
>> +struct trace_array *trace_array_lookup(const char *name);
>> int trace_set_clr_event(const char *system, const char *event, int set);
>> +int trace_array_set_clr_event(struct trace_array *tr, const char *system,
>> + const char *event, int set);
>>
>> /*
>> * The double __builtin_constant_p is because gcc will give us an error
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index a60dc13..1d171fd 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -8465,6 +8465,17 @@ static int instance_rmdir(const char *name)
>> return ret;
>> }
>>
>> +struct trace_array *trace_array_lookup(const char *name)
>> +{
>> + struct trace_array *tr;
>> + list_for_each_entry(tr, &ftrace_trace_arrays, list) {
> Accessing the ftrace_trace_arrays requires taking the trace_types_lock.
> It should also probably increment the ref counter too, and then
> trace_array_put() needs to be called.
>
> This prevents the trace array from being freed while something has
> access to it.
>
> -- Steve

Agree - Noted!

Also, adding a similar change for trace_array_create which also returns
a ptr to a newly created trace_array so will face the same issue.

Since trace_array_lookup and trace_array_create will be accompanied by a
trace_array_destroy once the use of the trace_array is done,
decrementing the reference ctr here.

Sending a v2 to address this.


Thanks,

Divya

>
>> + if (tr->name && strcmp(tr->name, name) == 0)
>> + return tr;
>> + }
>> + return NULL;
>> +}
>> +EXPORT_SYMBOL_GPL(trace_array_lookup);
>> +
>> static __init void create_trace_instances(struct dentry *d_tracer)
>> {
>> trace_instance_dir = tracefs_create_instance_dir("instances", d_tracer,
>> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
>> index 445b059..c126d2c 100644
>> --- a/kernel/trace/trace_events.c
>> +++ b/kernel/trace/trace_events.c
>> @@ -859,6 +859,28 @@ int trace_set_clr_event(const char *system, const char *event, int set)
>> }
>> EXPORT_SYMBOL_GPL(trace_set_clr_event);
>>
>> +/**
>> + * trace_array_set_clr_event - enable or disable an event for a trace array
>> + * @system: system name to match (NULL for any system)
>> + * @event: event name to match (NULL for all events, within system)
>> + * @set: 1 to enable, 0 to disable
>> + *
>> + * This is a way for other parts of the kernel to enable or disable
>> + * event recording to instances.
>> + *
>> + * Returns 0 on success, -EINVAL if the parameters do not match any
>> + * registered events.
>> + */
>> +int trace_array_set_clr_event(struct trace_array *tr, const char *system,
>> + const char *event, int set)
>> +{
>> + if (!tr)
>> + return -ENODEV;
>> +
>> + return __ftrace_set_clr_event(tr, NULL, system, event, set);
>> +}
>> +EXPORT_SYMBOL_GPL(trace_array_set_clr_event);
>> +
>> /* 128 should be much more than enough */
>> #define EVENT_BUF_SIZE 127
>>

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