linux-kernel - [PATCH 09/18] tracing: Modify soft-mode only if theres no other referrer

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Date:	Fri, 10 May 2013 20:12:15 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	David Sharp <dhsharp@...gle.com>,
	Hiraku Toyooka <hiraku.toyooka.gu@...achi.com>,
	Tom Zanussi <tom.zanussi@...el.com>
Subject: [PATCH 09/18] tracing: Modify soft-mode only if theres no other referrer

From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Modify soft-mode flag only if no other soft-mode referrer
(currently only the ftrace triggers) by using a reference
counter in each ftrace_event_file.

Without this fix, adding and removing several different
enable/disable_event triggers on the same event clear
soft-mode bit from the ftrace_event_file. This also
happens with a typo of glob on setting triggers.

e.g.

 # echo vfs_symlink:enable_event:net:netif_rx > set_ftrace_filter
 # cat events/net/netif_rx/enable
 0*
 # echo typo_func:enable_event:net:netif_rx > set_ftrace_filter
 # cat events/net/netif_rx/enable
 0
 # cat set_ftrace_filter
 #### all functions enabled ####
 vfs_symlink:enable_event:net:netif_rx:unlimited

As above, we still have a trigger, but soft-mode is gone.

Link: http://lkml.kernel.org/r/20130509054429.30398.7464.stgit@mhiramat-M0-7522

Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: David Sharp <dhsharp@...gle.com>
Cc: Hiraku Toyooka <hiraku.toyooka.gu@...achi.com>
Cc: Tom Zanussi <tom.zanussi@...el.com>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 include/linux/ftrace_event.h |    1 +
 kernel/trace/trace_events.c  |   12 ++++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 34e00fb..4372658 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -293,6 +293,7 @@ struct ftrace_event_file {
 	 * caching and such. Which is mostly OK ;-)
 	 */
 	unsigned long		flags;
+	atomic_t		sm_ref;	/* soft-mode reference counter */
 };
 
 #define __TRACE_EVENT_FLAGS(name, value)				\
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 915c136..8be1224 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -251,7 +251,8 @@ static int __ftrace_event_enable_disable(struct ftrace_event_file *file,
 	switch (enable) {
 	case 0:
 		/*
-		 * When soft_disable is set and enable is cleared, we want
+		 * When soft_disable is set and enable is cleared, the sm_ref
+		 * reference counter is decremented. If it reaches 0, we want
 		 * to clear the SOFT_DISABLED flag but leave the event in the
 		 * state that it was. That is, if the event was enabled and
 		 * SOFT_DISABLED isn't set, then do nothing. But if SOFT_DISABLED
@@ -263,6 +264,8 @@ static int __ftrace_event_enable_disable(struct ftrace_event_file *file,
 		 * "soft enable"s (clearing the SOFT_DISABLED bit) wont work.
 		 */
 		if (soft_disable) {
+			if (atomic_dec_return(&file->sm_ref) > 0)
+				break;
 			disable = file->flags & FTRACE_EVENT_FL_SOFT_DISABLED;
 			clear_bit(FTRACE_EVENT_FL_SOFT_MODE_BIT, &file->flags);
 		} else
@@ -291,8 +294,11 @@ static int __ftrace_event_enable_disable(struct ftrace_event_file *file,
 		 */
 		if (!soft_disable)
 			clear_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &file->flags);
-		else
+		else {
+			if (atomic_inc_return(&file->sm_ref) > 1)
+				break;
 			set_bit(FTRACE_EVENT_FL_SOFT_MODE_BIT, &file->flags);
+		}
 
 		if (!(file->flags & FTRACE_EVENT_FL_ENABLED)) {
 
@@ -1540,6 +1546,7 @@ __trace_add_new_event(struct ftrace_event_call *call,
 
 	file->event_call = call;
 	file->tr = tr;
+	atomic_set(&file->sm_ref, 0);
 	list_add(&file->list, &tr->events);
 
 	return event_create_dir(tr->event_dir, file, id, enable, filter, format);
@@ -1562,6 +1569,7 @@ __trace_early_add_new_event(struct ftrace_event_call *call,
 
 	file->event_call = call;
 	file->tr = tr;
+	atomic_set(&file->sm_ref, 0);
 	list_add(&file->list, &tr->events);
 
 	return 0;
-- 
1.7.10.4



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