Sorry for taking so long to getting to these patches. On Wed, 14 Aug 2019 10:55:26 -0700 Divya Indi <divya.i...@oracle.com> wrote:
> For functions returning a trace array Eg: trace_array_create(), we need to > increment the reference counter associated with the trace array to ensure it > does not get freed when in use. > > Once we are done using the trace array, we need to call > trace_array_put() to make sure we are not holding a reference to it > anymore and the instance/trace array can be removed when required. I think it would be more in line with other parts of the kernel if we don't need to do the trace_array_put() before calling trace_array_destroy(). That is, if we make the following change: diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 5ff206ce259e..ae12aac21c6c 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8527,9 +8527,11 @@ static int __remove_instance(struct trace_array *tr) { int i; - if (tr->ref || (tr->current_trace && tr->current_trace->ref)) + if (tr->ref > 1 || (tr->current_trace && tr->current_trace->ref)) return -EBUSY; + WARN_ON_ONCE(tr->ref != 1); + list_del(&tr->list); /* Disable all the flags that were enabled coming in */ > > Hence, additionally exporting trace_array_put(). > > Example use: > > tr = trace_array_create("foo-bar"); > // Use this trace array > // Log to this trace array or enable/disable events to this trace array. > .... > .... > // tr no longer required > trace_array_put(); > > Signed-off-by: Divya Indi <divya.i...@oracle.com> > --- > include/linux/trace.h | 1 + > kernel/trace/trace.c | 41 ++++++++++++++++++++++++++++++++++++++++- > 2 files changed, 41 insertions(+), 1 deletion(-) > > diff --git a/include/linux/trace.h b/include/linux/trace.h > index 24fcf07..2c782d5 100644 > --- a/include/linux/trace.h > +++ b/include/linux/trace.h > @@ -31,6 +31,7 @@ int trace_array_printk(struct trace_array *tr, unsigned > long ip, > const char *fmt, ...); > struct trace_array *trace_array_create(const char *name); > int trace_array_destroy(struct trace_array *tr); > +void trace_array_put(struct trace_array *tr); > #endif /* CONFIG_TRACING */ > > #endif /* _LINUX_TRACE_H */ > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 22bf166..7b6a37a 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -297,12 +297,22 @@ static void __trace_array_put(struct trace_array > *this_tr) > this_tr->ref--; > } > > +/** > + * trace_array_put - Decrement reference counter for the given trace array. > + * @tr: Trace array for which reference counter needs to decrement. > + * > + * NOTE: Functions like trace_array_create increment the reference counter > for > + * the trace array to ensure they do not get freed while in use. Make sure to > + * call trace_array_put() when the use is done. This will ensure that the > + * instance can be later removed. > + */ > void trace_array_put(struct trace_array *this_tr) > { > mutex_lock(&trace_types_lock); > __trace_array_put(this_tr); > mutex_unlock(&trace_types_lock); > } > +EXPORT_SYMBOL_GPL(trace_array_put); > > int call_filter_check_discard(struct trace_event_call *call, void *rec, > struct ring_buffer *buffer, > @@ -8302,6 +8312,16 @@ static void update_tracer_options(struct trace_array > *tr) > mutex_unlock(&trace_types_lock); > } > > +/** > + * trace_array_create - Create a new trace array with the given name. > + * @name: The name of the trace array to be created. > + * > + * Create and return a trace array with given name if it does not exist. > + * > + * NOTE: The reference counter associated with the returned trace array is > + * incremented to ensure it is not freed when in use. Make sure to call > + * "trace_array_put" for this trace array when its use is done. > + */ > struct trace_array *trace_array_create(const char *name) > { > struct trace_array *tr; > @@ -8364,6 +8384,8 @@ struct trace_array *trace_array_create(const char *name) > > list_add(&tr->list, &ftrace_trace_arrays); > > + tr->ref++; > + > mutex_unlock(&trace_types_lock); > mutex_unlock(&event_mutex); > > @@ -8385,7 +8407,19 @@ struct trace_array *trace_array_create(const char > *name) > > static int instance_mkdir(const char *name) > { > - return PTR_ERR_OR_ZERO(trace_array_create(name)); > + struct trace_array *tr; > + > + tr = trace_array_create(name); > + if (IS_ERR(tr)) > + return PTR_ERR(tr); > + > + /* This function does not return a reference to the created trace array, > + * so the reference counter is to be 0 when it returns. > + * trace_array_create increments the ref counter, decrement it here > + * by calling trace_array_put() */ > + trace_array_put(tr); > + If we make it that the destroy needs tr->ref == 1, we can remove the above. > + return 0; > } > > static int __remove_instance(struct trace_array *tr) > @@ -8424,6 +8458,11 @@ static int __remove_instance(struct trace_array *tr) > return 0; > } > > +/* > + * NOTE: An instance cannot be removed if there is still a reference to it. > + * Make sure to call "trace_array_put" for a trace array returned by > functions > + * like trace_array_create(), otherwise trace_array_destroy will not succeed. > + */ And remove the above comment too. -- Steve > int trace_array_destroy(struct trace_array *this_tr) > { > struct trace_array *tr;