tracing: Modify soft-mode only if there's no other referrer

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>

1 files changed, 10 insertions, 2 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 915c136d7bd1..8be1224046f8 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;