tracing/filter: Swap entire filter of events

When creating a new filter, instead of allocating the filter to the
event call first and then processing the filter, it is easier to
process a temporary filter and then just swap it with the call filter.
By doing this, it simplifies the code.

A filter is allocated and processed, when it is done, it is
swapped with the call filter, synchronize_sched() is called to make
sure all callers are done with the old filter (filters are called
with premption disabled), and then the old filter is freed.

Cc: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 2403ce5..f5d335d 100644 (file)
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -425,10 +425,15 @@ int filter_match_preds(struct event_filter *filter, void *rec)
        struct filter_pred *preds;
        struct filter_pred *pred;
        struct filter_pred *root;
-       int n_preds = ACCESS_ONCE(filter->n_preds);
+       int n_preds;
        int done = 0;
 
        /* no filter is considered a match */
+       if (!filter)
+               return 1;
+
+       n_preds = filter->n_preds;
+
        if (!n_preds)
                return 1;
 
@@ -509,6 +514,9 @@ static void parse_error(struct filter_parse_state *ps, int err, int pos)
 
 static void remove_filter_string(struct event_filter *filter)
 {
+       if (!filter)
+               return;
+
        kfree(filter->filter_string);
        filter->filter_string = NULL;
 }
@@ -568,9 +576,10 @@ static void append_filter_err(struct filter_parse_state *ps,
 
 void print_event_filter(struct ftrace_event_call *call, struct trace_seq *s)
 {
-       struct event_filter *filter = call->filter;
+       struct event_filter *filter;
 
        mutex_lock(&event_mutex);
+       filter = call->filter;
        if (filter && filter->filter_string)
                trace_seq_printf(s, "%s\n", filter->filter_string);
        else
@@ -581,9 +590,10 @@ void print_event_filter(struct ftrace_event_call *call, struct trace_seq *s)
 void print_subsystem_event_filter(struct event_subsystem *system,
                                  struct trace_seq *s)
 {
-       struct event_filter *filter = system->filter;
+       struct event_filter *filter;
 
        mutex_lock(&event_mutex);
+       filter = system->filter;
        if (filter && filter->filter_string)
                trace_seq_printf(s, "%s\n", filter->filter_string);
        else
@@ -745,26 +755,9 @@ static void __free_preds(struct event_filter *filter)
        filter->n_preds = 0;
 }
 
-static void reset_preds(struct event_filter *filter)
-{
-       int n_preds = filter->n_preds;
-       int i;
-
-       filter->n_preds = 0;
-       filter->root = NULL;
-       if (!filter->preds)
-               return;
-
-       for (i = 0; i < n_preds; i++)
-               filter->preds[i].fn = filter_pred_none;
-}
-
-static void filter_disable_preds(struct ftrace_event_call *call)
+static void filter_disable(struct ftrace_event_call *call)
 {
-       struct event_filter *filter = call->filter;
-
        call->flags &= ~TRACE_EVENT_FL_FILTERED;
-       reset_preds(filter);
 }
 
 static void __free_filter(struct event_filter *filter)
@@ -777,11 +770,16 @@ static void __free_filter(struct event_filter *filter)
        kfree(filter);
 }
 
+/*
+ * Called when destroying the ftrace_event_call.
+ * The call is being freed, so we do not need to worry about
+ * the call being currently used. This is for module code removing
+ * the tracepoints from within it.
+ */
 void destroy_preds(struct ftrace_event_call *call)
 {
        __free_filter(call->filter);
        call->filter = NULL;
-       call->flags &= ~TRACE_EVENT_FL_FILTERED;
 }
 
 static struct event_filter *__alloc_filter(void)
@@ -789,11 +787,6 @@ static struct event_filter *__alloc_filter(void)
        struct event_filter *filter;
 
        filter = kzalloc(sizeof(*filter), GFP_KERNEL);
-       if (!filter)
-               return ERR_PTR(-ENOMEM);
-
-       filter->n_preds = 0;
-
        return filter;
 }
 
@@ -838,46 +831,28 @@ static int __alloc_preds(struct event_filter *filter, int n_preds)
        return 0;
 }
 
-static int init_filter(struct ftrace_event_call *call)
-{
-       if (call->filter)
-               return 0;
-
-       call->flags &= ~TRACE_EVENT_FL_FILTERED;
-       call->filter = __alloc_filter();
-       if (IS_ERR(call->filter))
-               return PTR_ERR(call->filter);
-
-       return 0;
-}
-
-static int init_subsystem_preds(struct event_subsystem *system)
+static void filter_free_subsystem_preds(struct event_subsystem *system)
 {
        struct ftrace_event_call *call;
-       int err;
 
        list_for_each_entry(call, &ftrace_events, list) {
                if (strcmp(call->class->system, system->name) != 0)
                        continue;
 
-               err = init_filter(call);
-               if (err)
-                       return err;
+               filter_disable(call);
+               remove_filter_string(call->filter);
        }
-
-       return 0;
 }
 
-static void filter_free_subsystem_preds(struct event_subsystem *system)
+static void filter_free_subsystem_filters(struct event_subsystem *system)
 {
        struct ftrace_event_call *call;
 
        list_for_each_entry(call, &ftrace_events, list) {
                if (strcmp(call->class->system, system->name) != 0)
                        continue;
-
-               filter_disable_preds(call);
-               remove_filter_string(call->filter);
+               __free_filter(call->filter);
+               call->filter = NULL;
        }
 }
 
@@ -1743,88 +1718,129 @@ fail:
        return err;
 }
 
+struct filter_list {
+       struct list_head        list;
+       struct event_filter     *filter;
+};
+
 static int replace_system_preds(struct event_subsystem *system,
                                struct filter_parse_state *ps,
                                char *filter_string)
 {
        struct ftrace_event_call *call;
+       struct filter_list *filter_item;
+       struct filter_list *tmp;
+       LIST_HEAD(filter_list);
        bool fail = true;
        int err;
 
        list_for_each_entry(call, &ftrace_events, list) {
-               struct event_filter *filter = call->filter;
 
                if (strcmp(call->class->system, system->name) != 0)
                        continue;
 
-               /* try to see if the filter can be applied */
-               err = replace_preds(call, filter, ps, filter_string, true);
+               /*
+                * Try to see if the filter can be applied
+                *  (filter arg is ignored on dry_run)
+                */
+               err = replace_preds(call, NULL, ps, filter_string, true);
                if (err)
                        goto fail;
        }
 
-       /* set all filter pred counts to zero */
        list_for_each_entry(call, &ftrace_events, list) {
-               struct event_filter *filter = call->filter;
+               struct event_filter *filter;
 
                if (strcmp(call->class->system, system->name) != 0)
                        continue;
 
-               reset_preds(filter);
-       }
+               filter_item = kzalloc(sizeof(*filter_item), GFP_KERNEL);
+               if (!filter_item)
+                       goto fail_mem;
 
-       /*
-        * Since some of the preds may be used under preemption
-        * we need to wait for them to finish before we may
-        * reallocate them.
-        */
-       synchronize_sched();
+               list_add_tail(&filter_item->list, &filter_list);
 
-       list_for_each_entry(call, &ftrace_events, list) {
-               struct event_filter *filter = call->filter;
+               filter_item->filter = __alloc_filter();
+               if (!filter_item->filter)
+                       goto fail_mem;
+               filter = filter_item->filter;
 
-               if (strcmp(call->class->system, system->name) != 0)
-                       continue;
+               /* Can only fail on no memory */
+               err = replace_filter_string(filter, filter_string);
+               if (err)
+                       goto fail_mem;
 
-               /* really apply the filter */
-               filter_disable_preds(call);
                err = replace_preds(call, filter, ps, filter_string, false);
-               if (err)
-                       filter_disable_preds(call);
-               else {
+               if (err) {
+                       filter_disable(call);
+                       parse_error(ps, FILT_ERR_BAD_SUBSYS_FILTER, 0);
+                       append_filter_err(ps, filter);
+               } else
                        call->flags |= TRACE_EVENT_FL_FILTERED;
-                       replace_filter_string(filter, filter_string);
-               }
+               /*
+                * Regardless of if this returned an error, we still
+                * replace the filter for the call.
+                */
+               filter = call->filter;
+               call->filter = filter_item->filter;
+               filter_item->filter = filter;
+
                fail = false;
        }
 
        if (fail)
                goto fail;
 
+       /*
+        * The calls can still be using the old filters.
+        * Do a synchronize_sched() to ensure all calls are
+        * done with them before we free them.
+        */
+       synchronize_sched();
+       list_for_each_entry_safe(filter_item, tmp, &filter_list, list) {
+               __free_filter(filter_item->filter);
+               list_del(&filter_item->list);
+               kfree(filter_item);
+       }
        return 0;
  fail:
+       /* No call succeeded */
+       list_for_each_entry_safe(filter_item, tmp, &filter_list, list) {
+               list_del(&filter_item->list);
+               kfree(filter_item);
+       }
        parse_error(ps, FILT_ERR_BAD_SUBSYS_FILTER, 0);
        return -EINVAL;
+ fail_mem:
+       /* If any call succeeded, we still need to sync */
+       if (!fail)
+               synchronize_sched();
+       list_for_each_entry_safe(filter_item, tmp, &filter_list, list) {
+               __free_filter(filter_item->filter);
+               list_del(&filter_item->list);
+               kfree(filter_item);
+       }
+       return -ENOMEM;
 }
 
 int apply_event_filter(struct ftrace_event_call *call, char *filter_string)
 {
-       int err;
        struct filter_parse_state *ps;
+       struct event_filter *filter;
+       struct event_filter *tmp;
+       int err = 0;
 
        mutex_lock(&event_mutex);
 
-       err = init_filter(call);
-       if (err)
-               goto out_unlock;
-
        if (!strcmp(strstrip(filter_string), "0")) {
-               filter_disable_preds(call);
-               reset_preds(call->filter);
+               filter_disable(call);
+               filter = call->filter;
+               if (!filter)
+                       goto out_unlock;
+               call->filter = NULL;
                /* Make sure the filter is not being used */
                synchronize_sched();
-               __free_preds(call->filter);
-               remove_filter_string(call->filter);
+               __free_filter(filter);
                goto out_unlock;
        }
 
@@ -1833,29 +1849,41 @@ int apply_event_filter(struct ftrace_event_call *call, char *filter_string)
        if (!ps)
                goto out_unlock;
 
-       filter_disable_preds(call);
-       replace_filter_string(call->filter, filter_string);
+       filter = __alloc_filter();
+       if (!filter) {
+               kfree(ps);
+               goto out_unlock;
+       }
+
+       replace_filter_string(filter, filter_string);
 
        parse_init(ps, filter_ops, filter_string);
        err = filter_parse(ps);
        if (err) {
-               append_filter_err(ps, call->filter);
+               append_filter_err(ps, filter);
                goto out;
        }
 
-       /*
-        * Make sure all the pred counts are zero so that
-        * no task is using it when we reallocate the preds array.
-        */
-       reset_preds(call->filter);
-       synchronize_sched();
-
-       err = replace_preds(call, call->filter, ps, filter_string, false);
-       if (err)
-               append_filter_err(ps, call->filter);
-       else
+       err = replace_preds(call, filter, ps, filter_string, false);
+       if (err) {
+               filter_disable(call);
+               append_filter_err(ps, filter);
+       } else
                call->flags |= TRACE_EVENT_FL_FILTERED;
 out:
+       /*
+        * Always swap the call filter with the new filter
+        * even if there was an error. If there was an error
+        * in the filter, we disable the filter and show the error
+        * string
+        */
+       tmp = call->filter;
+       call->filter = filter;
+       if (tmp) {
+               /* Make sure the call is done with the filter */
+               synchronize_sched();
+               __free_filter(tmp);
+       }
        filter_opstack_clear(ps);
        postfix_clear(ps);
        kfree(ps);
@@ -1868,18 +1896,21 @@ out_unlock:
 int apply_subsystem_event_filter(struct event_subsystem *system,
                                 char *filter_string)
 {
-       int err;
        struct filter_parse_state *ps;
+       struct event_filter *filter;
+       int err = 0;
 
        mutex_lock(&event_mutex);
 
-       err = init_subsystem_preds(system);
-       if (err)
-               goto out_unlock;
-
        if (!strcmp(strstrip(filter_string), "0")) {
                filter_free_subsystem_preds(system);
                remove_filter_string(system->filter);
+               filter = system->filter;
+               system->filter = NULL;
+               /* Ensure all filters are no longer used */
+               synchronize_sched();
+               filter_free_subsystem_filters(system);
+               __free_filter(filter);
                goto out_unlock;
        }
 
@@ -1888,7 +1919,17 @@ int apply_subsystem_event_filter(struct event_subsystem *system,
        if (!ps)
                goto out_unlock;
 
-       replace_filter_string(system->filter, filter_string);
+       filter = __alloc_filter();
+       if (!filter)
+               goto out;
+
+       replace_filter_string(filter, filter_string);
+       /*
+        * No event actually uses the system filter
+        * we can free it without synchronize_sched().
+        */
+       __free_filter(system->filter);
+       system->filter = filter;
 
        parse_init(ps, filter_ops, filter_string);
        err = filter_parse(ps);
@@ -1945,7 +1986,7 @@ int ftrace_profile_set_filter(struct perf_event *event, int event_id,
                goto out_unlock;
 
        filter = __alloc_filter();
-       if (IS_ERR(filter)) {
+       if (!filter) {
                err = PTR_ERR(filter);
                goto out_unlock;
        }