From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966297AbcKKDit (ORCPT ); Thu, 10 Nov 2016 22:38:49 -0500 Received: from mail-wm0-f45.google.com ([74.125.82.45]:35811 "EHLO mail-wm0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965233AbcKKDir (ORCPT ); Thu, 10 Nov 2016 22:38:47 -0500 MIME-Version: 1.0 From: Chunyan Zhang Date: Fri, 11 Nov 2016 11:38:45 +0800 Message-ID: Subject: To: Steven Rostedt Cc: Mathieu Poirier , Alexander Shishkin , mingo@redhat.com, Mike Leach , Tor Jeremiassen , philippe.langlais@st.com, Nicolas GUION , Felipe Balbi , Lyra Zhang , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steven, On 21 October 2016 at 20:13, Chunyan Zhang wrote: > On 18 October 2016 at 23:44, Steven Rostedt wrote: >> On Tue, 18 Oct 2016 16:08:58 +0800 >> Chunyan Zhang wrote: >> >>> Currently Function traces can be only exported to ring buffer, this >>> patch added trace_export concept which can process traces and export >>> them to a registered destination as an addition to the current only >>> one output of Ftrace - i.e. ring buffer. >>> >>> In this way, if we want Function traces to be sent to other destination >>> rather than ring buffer only, 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 trace (trace type is TRACE_FN) >>> is supported. >> >> This is getting better, but I still have some nits. >> > > Thanks. > >>> >>> Signed-off-by: Chunyan Zhang >>> --- >>> include/linux/trace.h | 28 +++++++++++ >>> kernel/trace/trace.c | 132 +++++++++++++++++++++++++++++++++++++++++++++++++- >>> 2 files changed, 159 insertions(+), 1 deletion(-) >>> create mode 100644 include/linux/trace.h >>> >>> diff --git a/include/linux/trace.h b/include/linux/trace.h >>> new file mode 100644 >>> index 0000000..eb1c5b8 >>> --- /dev/null >>> +++ b/include/linux/trace.h >>> @@ -0,0 +1,28 @@ >>> +#ifndef _LINUX_TRACE_H >>> +#define _LINUX_TRACE_H >>> + >>> +#ifdef CONFIG_TRACING >>> +/* >>> + * The trace export - an export of Ftrace output. The trace_export >>> + * can process traces and export them to a registered destination as >>> + * an addition to the current only output of Ftrace - i.e. ring buffer. >>> + * >>> + * If you want traces to be sent to some other place rather than ring >>> + * buffer only, just need to register a new trace_export and implement >>> + * its own .write() function for writing traces to the storage. >>> + * >>> + * next - pointer to the next trace_export >>> + * write - copy traces which have been delt with ->commit() to >>> + * the destination >>> + */ >>> +struct trace_export { >>> + struct trace_export __rcu *next; >>> + void (*write)(const char *, unsigned int); >> >> Why const char*? Why not const void *? This will never be a string. >> > > Will revise this. > >> >>> +}; >>> + >>> +int register_ftrace_export(struct trace_export *export); >>> +int unregister_ftrace_export(struct trace_export *export); >>> + >>> +#endif /* CONFIG_TRACING */ >>> + >>> +#endif /* _LINUX_TRACE_H */ >>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c >>> index 8696ce6..db94ec1 100644 >>> --- a/kernel/trace/trace.c >>> +++ b/kernel/trace/trace.c >>> @@ -40,6 +40,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> #include >>> >>> #include "trace.h" >>> @@ -2128,6 +2129,132 @@ void trace_buffer_unlock_commit_regs(struct trace_array *tr, >>> ftrace_trace_userstack(buffer, flags, pc); >>> } >>> >>> +static void >>> +trace_process_export(struct trace_export *export, >>> + struct ring_buffer_event *event) >>> +{ >>> + struct trace_entry *entry; >>> + unsigned int size = 0; >>> + >>> + entry = ring_buffer_event_data(event); >>> + >>> + size = ring_buffer_event_length(event); >>> + >>> + if (export->write) >>> + export->write((char *)entry, size); >> >> Is there ever going to be a time where export->write wont be set? > > There hasn't been since only one trace_export (i.e. stm_ftrace) was > added in this patch-set , I just wanted to make sure the write() has > been set before registering trace_export like what I added in 2/3 of > this series. > >> >> And if there is, this can be racy. As in >> >> >> CPU 0: CPU 1: >> ------ ------ >> if (export->write) >> >> export->write = NULL; > > Is there going to be this kind of use case? Why some one needs to > change export->write() rather than register a new trace_export? > > I probably haven't understood your point thoroughly, please correct me > if my guess was wrong. > Any further comments? :) Thanks, Chunyan > > Thanks for the review, > Chunyan > >> >> export->write(entry, size); >> >> BOOM! >> >> >> -- Steve >> >>> +} >>> + >>> +static DEFINE_MUTEX(ftrace_export_lock); >>> + >>> +static struct trace_export __rcu *ftrace_exports_list __read_mostly; >>> + >>> +static DEFINE_STATIC_KEY_FALSE(ftrace_exports_enabled); >>> + >>> +static inline void ftrace_exports_enable(void) >>> +{ >>> + static_branch_enable(&ftrace_exports_enabled); >>> +} >>> + >>> +static inline void ftrace_exports_disable(void) >>> +{ >>> + static_branch_disable(&ftrace_exports_enabled); >>> +} >>> + >>> +void ftrace_exports(struct ring_buffer_event *event) >>> +{ >>> + struct trace_export *export; >>> + >>> + preempt_disable_notrace(); >>> + >>> + export = rcu_dereference_raw_notrace(ftrace_exports_list); >>> + while (export) { >>> + trace_process_export(export, event); >>> + export = rcu_dereference_raw_notrace(export->next); >>> + } >>> + >>> + preempt_enable_notrace(); >>> +} >>> + >>> +static inline void >>> +add_trace_export(struct trace_export **list, struct trace_export *export) >>> +{ >>> + rcu_assign_pointer(export->next, *list); >>> + /* >>> + * We are entering export into the list but another >>> + * CPU might be walking that list. We need to make sure >>> + * the export->next pointer is valid before another CPU sees >>> + * the export pointer included into the list. >>> + */ >>> + rcu_assign_pointer(*list, export); >>> +} >>> + >>> +static inline int >>> +rm_trace_export(struct trace_export **list, struct trace_export *export) >>> +{ >>> + struct trace_export **p; >>> + >>> + for (p = list; *p != NULL; p = &(*p)->next) >>> + if (*p == export) >>> + break; >>> + >>> + if (*p != export) >>> + return -1; >>> + >>> + rcu_assign_pointer(*p, (*p)->next); >>> + >>> + return 0; >>> +} >>> + >>> +static inline void >>> +add_ftrace_export(struct trace_export **list, struct trace_export *export) >>> +{ >>> + if (*list == NULL) >>> + ftrace_exports_enable(); >>> + >>> + add_trace_export(list, export); >>> +} >>> + >>> +static inline int >>> +rm_ftrace_export(struct trace_export **list, struct trace_export *export) >>> +{ >>> + int ret; >>> + >>> + ret = rm_trace_export(list, export); >>> + if (*list == NULL) >>> + ftrace_exports_disable(); >>> + >>> + return ret; >>> +} >>> + >>> +int register_ftrace_export(struct trace_export *export) >>> +{ >>> + if (WARN_ON_ONCE(!export->write)) >>> + return -1; >>> + >>> + mutex_lock(&ftrace_export_lock); >>> + >>> + add_ftrace_export(&ftrace_exports_list, export); >>> + >>> + mutex_unlock(&ftrace_export_lock); >>> + >>> + return 0; >>> +} >>> +EXPORT_SYMBOL_GPL(register_ftrace_export); >>> + >>> +int unregister_ftrace_export(struct trace_export *export) >>> +{ >>> + int ret; >>> + >>> + mutex_lock(&ftrace_export_lock); >>> + >>> + ret = rm_ftrace_export(&ftrace_exports_list, export); >>> + >>> + mutex_unlock(&ftrace_export_lock); >>> + >>> + return ret; >>> +} >>> +EXPORT_SYMBOL_GPL(unregister_ftrace_export); >>> + >>> void >>> trace_function(struct trace_array *tr, >>> unsigned long ip, unsigned long parent_ip, unsigned long flags, >>> @@ -2146,8 +2273,11 @@ trace_function(struct trace_array *tr, >>> entry->ip = ip; >>> entry->parent_ip = parent_ip; >>> >>> - if (!call_filter_check_discard(call, entry, buffer, event)) >>> + if (!call_filter_check_discard(call, entry, buffer, event)) { >>> + if (static_branch_unlikely(&ftrace_exports_enabled)) >>> + ftrace_exports(event); >>> __buffer_unlock_commit(buffer, event); >>> + } >>> } >>> >>> #ifdef CONFIG_STACKTRACE >>