tracing: Add hook to function tracing for other subsystems to use
Currently Function traces can be only exported to the ring buffer. This adds a trace_export concept which can process traces and export them to a registered destination as an addition to the current one that outputs to Ftrace - i.e. ring buffer. In this way, if we want function traces to be sent to other destinations rather than only to the ring buffer, we just need to register a new trace_export and implement its own .write() function for writing traces to storage. With this patch, only function tracing (trace type is TRACE_FN) is supported. Link: http://lkml.kernel.org/r/1479715043-6534-2-git-send-email-zhang.chunyan@linaro.org Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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include/linux/trace.h
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28
include/linux/trace.h
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#ifndef _LINUX_TRACE_H
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#define _LINUX_TRACE_H
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#ifdef CONFIG_TRACING
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/*
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* The trace export - an export of Ftrace output. The trace_export
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* can process traces and export them to a registered destination as
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* an addition to the current only output of Ftrace - i.e. ring buffer.
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*
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* If you want traces to be sent to some other place rather than ring
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* buffer only, just need to register a new trace_export and implement
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* its own .write() function for writing traces to the storage.
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*
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* next - pointer to the next trace_export
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* write - copy traces which have been delt with ->commit() to
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* the destination
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*/
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struct trace_export {
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struct trace_export __rcu *next;
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void (*write)(const void *, unsigned int);
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};
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int register_ftrace_export(struct trace_export *export);
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int unregister_ftrace_export(struct trace_export *export);
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#endif /* CONFIG_TRACING */
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#endif /* _LINUX_TRACE_H */
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@ -40,6 +40,7 @@
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#include <linux/poll.h>
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#include <linux/nmi.h>
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#include <linux/fs.h>
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#include <linux/trace.h>
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#include <linux/sched/rt.h>
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#include "trace.h"
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@ -2128,6 +2129,129 @@ void trace_buffer_unlock_commit_regs(struct trace_array *tr,
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ftrace_trace_userstack(buffer, flags, pc);
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}
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static void
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trace_process_export(struct trace_export *export,
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struct ring_buffer_event *event)
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{
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struct trace_entry *entry;
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unsigned int size = 0;
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entry = ring_buffer_event_data(event);
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size = ring_buffer_event_length(event);
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export->write(entry, size);
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}
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static DEFINE_MUTEX(ftrace_export_lock);
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static struct trace_export __rcu *ftrace_exports_list __read_mostly;
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static DEFINE_STATIC_KEY_FALSE(ftrace_exports_enabled);
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static inline void ftrace_exports_enable(void)
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{
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static_branch_enable(&ftrace_exports_enabled);
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}
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static inline void ftrace_exports_disable(void)
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{
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static_branch_disable(&ftrace_exports_enabled);
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}
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void ftrace_exports(struct ring_buffer_event *event)
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{
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struct trace_export *export;
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preempt_disable_notrace();
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export = rcu_dereference_raw_notrace(ftrace_exports_list);
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while (export) {
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trace_process_export(export, event);
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export = rcu_dereference_raw_notrace(export->next);
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}
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preempt_enable_notrace();
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}
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static inline void
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add_trace_export(struct trace_export **list, struct trace_export *export)
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{
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rcu_assign_pointer(export->next, *list);
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/*
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* We are entering export into the list but another
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* CPU might be walking that list. We need to make sure
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* the export->next pointer is valid before another CPU sees
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* the export pointer included into the list.
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*/
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rcu_assign_pointer(*list, export);
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}
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static inline int
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rm_trace_export(struct trace_export **list, struct trace_export *export)
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{
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struct trace_export **p;
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for (p = list; *p != NULL; p = &(*p)->next)
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if (*p == export)
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break;
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if (*p != export)
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return -1;
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rcu_assign_pointer(*p, (*p)->next);
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return 0;
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}
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static inline void
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add_ftrace_export(struct trace_export **list, struct trace_export *export)
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{
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if (*list == NULL)
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ftrace_exports_enable();
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add_trace_export(list, export);
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}
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static inline int
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rm_ftrace_export(struct trace_export **list, struct trace_export *export)
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{
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int ret;
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ret = rm_trace_export(list, export);
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if (*list == NULL)
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ftrace_exports_disable();
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return ret;
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}
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int register_ftrace_export(struct trace_export *export)
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{
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if (WARN_ON_ONCE(!export->write))
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return -1;
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mutex_lock(&ftrace_export_lock);
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add_ftrace_export(&ftrace_exports_list, export);
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mutex_unlock(&ftrace_export_lock);
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return 0;
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}
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EXPORT_SYMBOL_GPL(register_ftrace_export);
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int unregister_ftrace_export(struct trace_export *export)
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{
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int ret;
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mutex_lock(&ftrace_export_lock);
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ret = rm_ftrace_export(&ftrace_exports_list, export);
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mutex_unlock(&ftrace_export_lock);
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return ret;
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}
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EXPORT_SYMBOL_GPL(unregister_ftrace_export);
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void
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trace_function(struct trace_array *tr,
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unsigned long ip, unsigned long parent_ip, unsigned long flags,
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entry->ip = ip;
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entry->parent_ip = parent_ip;
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if (!call_filter_check_discard(call, entry, buffer, event))
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if (!call_filter_check_discard(call, entry, buffer, event)) {
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if (static_branch_unlikely(&ftrace_exports_enabled))
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ftrace_exports(event);
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__buffer_unlock_commit(buffer, event);
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}
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}
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#ifdef CONFIG_STACKTRACE
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