tracing: Modify soft-mode only if there's no other referrer
Masami Hiramatsu [Thu, 9 May 2013 05:44:29 +0000 (14:44 +0900)]
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
kernel/trace/trace_events.c

index 34e00fb..4372658 100644 (file)
@@ -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)                               \
index 915c136..8be1224 100644 (file)
@@ -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;