Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756376AbcKWC1W (ORCPT ); Tue, 22 Nov 2016 21:27:22 -0500 Received: from mail-qk0-f180.google.com ([209.85.220.180]:36442 "EHLO mail-qk0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755349AbcKWC1U (ORCPT ); Tue, 22 Nov 2016 21:27:20 -0500 MIME-Version: 1.0 In-Reply-To: <20161122173950.56585f50@gandalf.local.home> References: <1479715043-6534-1-git-send-email-zhang.chunyan@linaro.org> <1479715043-6534-2-git-send-email-zhang.chunyan@linaro.org> <20161122173950.56585f50@gandalf.local.home> From: Chunyan Zhang Date: Wed, 23 Nov 2016 10:27:18 +0800 Message-ID: Subject: Re: [PATCH V9 1/6] tracing: add a possibility of exporting function trace to other places instead of ring buffer only 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 Content-Length: 7153 Lines: 229 On 23 November 2016 at 06:39, Steven Rostedt wrote: > On Mon, 21 Nov 2016 15:57:18 +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. >> >> Signed-off-by: Chunyan Zhang >> --- >> include/linux/trace.h | 28 +++++++++++ >> kernel/trace/trace.c | 129 +++++++++++++++++++++++++++++++++++++++++++++++++- >> 2 files changed, 156 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..9330a58 >> --- /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 void *, unsigned int); >> +}; >> + >> +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..038291d 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 +2129,129 @@ 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); >> + export->write(entry, size); >> +} >> + >> +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) > > I'm currently testing the patches, but is there a reason that > ftrace_exports() is not static? At present ftrace_exports() is only used by function trace though, but I hope it can be used by other traces when it needed. So I didn't mark it with static, but if you think it should better be static for the time being, I can revise that. Thanks, Chunyan > > -- Steve > >> +{ >> + 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 +2270,11 @@ 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 >