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>

1 files changed, 146 insertions, 105 deletions

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 2403ce5b6507..f5d335d28d0b 100644
--- 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;
         }