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

Steven Rostedt
2013-05-11T00:13:36Z

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From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.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@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: David Sharp <dhsharp@google.com>
Cc: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Cc: Tom Zanussi <tom.zanussi@intel.com>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.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;