tracing/filter: Use a tree instead of stack for filter_match_preds()
Currently the filter_match_preds() requires a stack to push
and pop the preds to determine if the filter matches the record or not.
This has two drawbacks:
1) It requires a stack to store state information. As this is done
in fast paths we can't allocate the storage for this stack, and
we can't use a global as it must be re-entrant. The stack is stored
on the kernel stack and this greatly limits how many preds we
may allow.
2) All conditions are calculated even when a short circuit exists.
a || b will always calculate a and b even though a was determined
to be true.
Using a tree we can walk a constant structure that will save
the state as we go. The algorithm is simply:
pred = root;
do {
switch (move) {
case MOVE_DOWN:
if (OR or AND) {
pred = left;
continue;
}
if (pred == root)
break;
match = pred->fn();
pred = pred->parent;
move = left child ? MOVE_UP_FROM_LEFT : MOVE_UP_FROM_RIGHT;
continue;
case MOVE_UP_FROM_LEFT:
/* Only OR or AND can be a parent */
if (match && OR || !match && AND) {
/* short circuit */
if (pred == root)
break;
pred = pred->parent;
move = left child ?
MOVE_UP_FROM_LEFT :
MOVE_UP_FROM_RIGHT;
continue;
}
pred = pred->right;
move = MOVE_DOWN;
continue;
case MOVE_UP_FROM_RIGHT:
if (pred == root)
break;
pred = pred->parent;
move = left child ? MOVE_UP_FROM_LEFT : MOVE_UP_FROM_RIGHT;
continue;
}
done = 1;
} while (!done);
This way there's no strict limit to how many preds we allow
and it also will short circuit the logical operations when possible.
Cc: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt
Steven Rostedt
parent
f76690afd0
commit
61e9dea20e
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@ -664,6 +664,7 @@ struct event_filter {
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int n_preds; /* Number assigned */
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int a_preds; /* allocated */
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struct filter_pred *preds;
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struct filter_pred *root;
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char *filter_string;
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};
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@ -675,6 +676,9 @@ struct event_subsystem {
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int nr_events;
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};
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#define FILTER_PRED_INVALID ((unsigned short)-1)
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#define FILTER_PRED_IS_RIGHT (1 << 15)
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struct filter_pred;
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struct regex;
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@ -704,7 +708,10 @@ struct filter_pred {
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int offset;
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int not;
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int op;
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int pop_n;
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unsigned short index;
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unsigned short parent;
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unsigned short left;
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unsigned short right;
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};
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extern struct list_head ftrace_common_fields;
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@ -123,6 +123,11 @@ struct filter_parse_state {
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} operand;
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};
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struct pred_stack {
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struct filter_pred **preds;
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int index;
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};
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#define DEFINE_COMPARISON_PRED(type) \
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static int filter_pred_##type(struct filter_pred *pred, void *event) \
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{ \
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@ -357,52 +362,95 @@ static void filter_build_regex(struct filter_pred *pred)
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pred->not ^= not;
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}
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enum move_type {
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MOVE_DOWN,
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MOVE_UP_FROM_LEFT,
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MOVE_UP_FROM_RIGHT
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};
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static struct filter_pred *
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get_pred_parent(struct filter_pred *pred, struct filter_pred *preds,
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int index, enum move_type *move)
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{
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if (pred->parent & FILTER_PRED_IS_RIGHT)
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*move = MOVE_UP_FROM_RIGHT;
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else
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*move = MOVE_UP_FROM_LEFT;
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pred = &preds[pred->parent & ~FILTER_PRED_IS_RIGHT];
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return pred;
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}
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/* return 1 if event matches, 0 otherwise (discard) */
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int filter_match_preds(struct event_filter *filter, void *rec)
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{
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int match = -1, top = 0, val1 = 0, val2 = 0;
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int stack[MAX_FILTER_PRED];
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int match = -1;
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enum move_type move = MOVE_DOWN;
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struct filter_pred *preds;
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struct filter_pred *pred;
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struct filter_pred *root;
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int n_preds = ACCESS_ONCE(filter->n_preds);
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int i;
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int done = 0;
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/* no filter is considered a match */
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if (!n_preds)
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return 1;
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/*
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* n_preds and filter->preds is protect with preemption disabled.
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* n_preds, root and filter->preds are protect with preemption disabled.
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*/
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preds = rcu_dereference_sched(filter->preds);
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root = rcu_dereference_sched(filter->root);
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if (!root)
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return 1;
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for (i = 0; i < n_preds; i++) {
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pred = &preds[i];
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if (!pred->pop_n) {
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pred = root;
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/* match is currently meaningless */
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match = -1;
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do {
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switch (move) {
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case MOVE_DOWN:
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/* only AND and OR have children */
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if (pred->left != FILTER_PRED_INVALID) {
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/* keep going to leaf node */
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pred = &preds[pred->left];
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continue;
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}
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match = pred->fn(pred, rec);
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stack[top++] = match;
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/* If this pred is the only pred */
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if (pred == root)
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break;
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pred = get_pred_parent(pred, preds,
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pred->parent, &move);
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continue;
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case MOVE_UP_FROM_LEFT:
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/* Check for short circuits */
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if ((match && pred->op == OP_OR) ||
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(!match && pred->op == OP_AND)) {
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if (pred == root)
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break;
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pred = get_pred_parent(pred, preds,
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pred->parent, &move);
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continue;
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}
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/* now go down the right side of the tree. */
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pred = &preds[pred->right];
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move = MOVE_DOWN;
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continue;
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case MOVE_UP_FROM_RIGHT:
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/* We finished this equation. */
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if (pred == root)
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break;
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pred = get_pred_parent(pred, preds,
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pred->parent, &move);
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continue;
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}
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if (pred->pop_n > top) {
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WARN_ON_ONCE(1);
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return 0;
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}
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val1 = stack[--top];
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val2 = stack[--top];
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switch (pred->op) {
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case OP_AND:
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match = val1 && val2;
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break;
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case OP_OR:
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match = val1 || val2;
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break;
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default:
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WARN_ONCE(1, "filter op is not AND or OR");
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}
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stack[top++] = match;
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}
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done = 1;
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} while (!done);
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return stack[--top];
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return match;
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}
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EXPORT_SYMBOL_GPL(filter_match_preds);
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@ -539,10 +587,58 @@ static void filter_clear_pred(struct filter_pred *pred)
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pred->regex.len = 0;
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}
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static int filter_set_pred(struct filter_pred *dest,
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static int __alloc_pred_stack(struct pred_stack *stack, int n_preds)
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{
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stack->preds = kzalloc(sizeof(*stack->preds)*(n_preds + 1), GFP_KERNEL);
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if (!stack->preds)
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return -ENOMEM;
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stack->index = n_preds;
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return 0;
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}
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static void __free_pred_stack(struct pred_stack *stack)
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{
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kfree(stack->preds);
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stack->index = 0;
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}
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static int __push_pred_stack(struct pred_stack *stack,
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struct filter_pred *pred)
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{
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int index = stack->index;
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if (WARN_ON(index == 0))
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return -ENOSPC;
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stack->preds[--index] = pred;
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stack->index = index;
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return 0;
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}
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static struct filter_pred *
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__pop_pred_stack(struct pred_stack *stack)
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{
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struct filter_pred *pred;
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int index = stack->index;
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pred = stack->preds[index++];
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if (!pred)
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return NULL;
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stack->index = index;
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return pred;
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}
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static int filter_set_pred(struct event_filter *filter,
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int idx,
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struct pred_stack *stack,
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struct filter_pred *src,
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filter_pred_fn_t fn)
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{
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struct filter_pred *dest = &filter->preds[idx];
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struct filter_pred *left;
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struct filter_pred *right;
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*dest = *src;
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if (src->field_name) {
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dest->field_name = kstrdup(src->field_name, GFP_KERNEL);
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@ -550,8 +646,25 @@ static int filter_set_pred(struct filter_pred *dest,
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return -ENOMEM;
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}
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dest->fn = fn;
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dest->index = idx;
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return 0;
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if (dest->op == OP_OR || dest->op == OP_AND) {
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right = __pop_pred_stack(stack);
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left = __pop_pred_stack(stack);
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if (!left || !right)
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return -EINVAL;
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dest->left = left->index;
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dest->right = right->index;
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left->parent = dest->index;
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right->parent = dest->index | FILTER_PRED_IS_RIGHT;
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} else
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/*
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* Make dest->left invalid to be used as a quick
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* way to know this is a leaf node.
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*/
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dest->left = FILTER_PRED_INVALID;
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return __push_pred_stack(stack, dest);
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}
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static void __free_preds(struct event_filter *filter)
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@ -574,6 +687,7 @@ static void reset_preds(struct event_filter *filter)
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int i;
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filter->n_preds = 0;
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filter->root = NULL;
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if (!filter->preds)
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return;
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@ -707,6 +821,7 @@ static int filter_add_pred_fn(struct filter_parse_state *ps,
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struct ftrace_event_call *call,
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struct event_filter *filter,
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struct filter_pred *pred,
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struct pred_stack *stack,
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filter_pred_fn_t fn)
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{
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int idx, err;
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@ -718,7 +833,7 @@ static int filter_add_pred_fn(struct filter_parse_state *ps,
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idx = filter->n_preds;
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filter_clear_pred(&filter->preds[idx]);
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err = filter_set_pred(&filter->preds[idx], pred, fn);
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err = filter_set_pred(filter, idx, stack, pred, fn);
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if (err)
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return err;
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@ -803,6 +918,7 @@ static int filter_add_pred(struct filter_parse_state *ps,
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struct ftrace_event_call *call,
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struct event_filter *filter,
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struct filter_pred *pred,
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struct pred_stack *stack,
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bool dry_run)
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{
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struct ftrace_event_field *field;
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@ -812,13 +928,10 @@ static int filter_add_pred(struct filter_parse_state *ps,
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fn = pred->fn = filter_pred_none;
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if (pred->op == OP_AND) {
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pred->pop_n = 2;
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if (pred->op == OP_AND)
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goto add_pred_fn;
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} else if (pred->op == OP_OR) {
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pred->pop_n = 2;
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else if (pred->op == OP_OR)
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goto add_pred_fn;
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}
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field = find_event_field(call, pred->field_name);
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if (!field) {
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@ -867,7 +980,7 @@ static int filter_add_pred(struct filter_parse_state *ps,
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add_pred_fn:
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if (!dry_run)
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return filter_add_pred_fn(ps, call, filter, pred, fn);
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return filter_add_pred_fn(ps, call, filter, pred, stack, fn);
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return 0;
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}
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@ -1248,6 +1361,7 @@ static int replace_preds(struct ftrace_event_call *call,
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char *operand1 = NULL, *operand2 = NULL;
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struct filter_pred *pred;
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struct postfix_elt *elt;
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struct pred_stack stack = { }; /* init to NULL */
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int err;
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int n_preds = 0;
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@ -1262,9 +1376,12 @@ static int replace_preds(struct ftrace_event_call *call,
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return err;
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if (!dry_run) {
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err = __alloc_preds(filter, n_preds);
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err = __alloc_pred_stack(&stack, n_preds);
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if (err)
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return err;
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err = __alloc_preds(filter, n_preds);
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if (err)
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goto fail;
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}
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n_preds = 0;
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@ -1276,14 +1393,16 @@ static int replace_preds(struct ftrace_event_call *call,
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operand2 = elt->operand;
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else {
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parse_error(ps, FILT_ERR_TOO_MANY_OPERANDS, 0);
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return -EINVAL;
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err = -EINVAL;
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goto fail;
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}
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continue;
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}
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if (WARN_ON(n_preds++ == MAX_FILTER_PRED)) {
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parse_error(ps, FILT_ERR_TOO_MANY_PREDS, 0);
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return -ENOSPC;
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err = -ENOSPC;
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goto fail;
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}
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if (elt->op == OP_AND || elt->op == OP_OR) {
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@ -1293,22 +1412,44 @@ static int replace_preds(struct ftrace_event_call *call,
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if (!operand1 || !operand2) {
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parse_error(ps, FILT_ERR_MISSING_FIELD, 0);
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return -EINVAL;
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err = -EINVAL;
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goto fail;
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}
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pred = create_pred(elt->op, operand1, operand2);
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add_pred:
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if (!pred)
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return -ENOMEM;
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err = filter_add_pred(ps, call, filter, pred, dry_run);
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if (!pred) {
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err = -ENOMEM;
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goto fail;
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}
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err = filter_add_pred(ps, call, filter, pred, &stack, dry_run);
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filter_free_pred(pred);
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if (err)
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return err;
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goto fail;
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operand1 = operand2 = NULL;
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}
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return 0;
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if (!dry_run) {
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/* We should have one item left on the stack */
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pred = __pop_pred_stack(&stack);
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if (!pred)
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return -EINVAL;
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/* This item is where we start from in matching */
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filter->root = pred;
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/* Make sure the stack is empty */
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pred = __pop_pred_stack(&stack);
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if (WARN_ON(pred)) {
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err = -EINVAL;
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filter->root = NULL;
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goto fail;
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}
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}
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err = 0;
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fail:
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__free_pred_stack(&stack);
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return err;
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}
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static int replace_system_preds(struct event_subsystem *system,
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