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 2011-01-27 22:54:33 -05:00 committed by Steven Rostedt
parent f76690afd0
commit 61e9dea20e
2 changed files with 194 additions and 46 deletions

View File

@ -664,6 +664,7 @@ struct event_filter {
int n_preds; /* Number assigned */
int a_preds; /* allocated */
struct filter_pred *preds;
struct filter_pred *root;
char *filter_string;
};
@ -675,6 +676,9 @@ struct event_subsystem {
int nr_events;
};
#define FILTER_PRED_INVALID ((unsigned short)-1)
#define FILTER_PRED_IS_RIGHT (1 << 15)
struct filter_pred;
struct regex;
@ -704,7 +708,10 @@ struct filter_pred {
int offset;
int not;
int op;
int pop_n;
unsigned short index;
unsigned short parent;
unsigned short left;
unsigned short right;
};
extern struct list_head ftrace_common_fields;

View File

@ -123,6 +123,11 @@ struct filter_parse_state {
} operand;
};
struct pred_stack {
struct filter_pred **preds;
int index;
};
#define DEFINE_COMPARISON_PRED(type) \
static int filter_pred_##type(struct filter_pred *pred, void *event) \
{ \
@ -357,52 +362,95 @@ static void filter_build_regex(struct filter_pred *pred)
pred->not ^= not;
}
enum move_type {
MOVE_DOWN,
MOVE_UP_FROM_LEFT,
MOVE_UP_FROM_RIGHT
};
static struct filter_pred *
get_pred_parent(struct filter_pred *pred, struct filter_pred *preds,
int index, enum move_type *move)
{
if (pred->parent & FILTER_PRED_IS_RIGHT)
*move = MOVE_UP_FROM_RIGHT;
else
*move = MOVE_UP_FROM_LEFT;
pred = &preds[pred->parent & ~FILTER_PRED_IS_RIGHT];
return pred;
}
/* return 1 if event matches, 0 otherwise (discard) */
int filter_match_preds(struct event_filter *filter, void *rec)
{
int match = -1, top = 0, val1 = 0, val2 = 0;
int stack[MAX_FILTER_PRED];
int match = -1;
enum move_type move = MOVE_DOWN;
struct filter_pred *preds;
struct filter_pred *pred;
struct filter_pred *root;
int n_preds = ACCESS_ONCE(filter->n_preds);
int i;
int done = 0;
/* no filter is considered a match */
if (!n_preds)
return 1;
/*
* n_preds and filter->preds is protect with preemption disabled.
* n_preds, root and filter->preds are protect with preemption disabled.
*/
preds = rcu_dereference_sched(filter->preds);
root = rcu_dereference_sched(filter->root);
if (!root)
return 1;
for (i = 0; i < n_preds; i++) {
pred = &preds[i];
if (!pred->pop_n) {
pred = root;
/* match is currently meaningless */
match = -1;
do {
switch (move) {
case MOVE_DOWN:
/* only AND and OR have children */
if (pred->left != FILTER_PRED_INVALID) {
/* keep going to leaf node */
pred = &preds[pred->left];
continue;
}
match = pred->fn(pred, rec);
stack[top++] = match;
/* If this pred is the only pred */
if (pred == root)
break;
pred = get_pred_parent(pred, preds,
pred->parent, &move);
continue;
case MOVE_UP_FROM_LEFT:
/* Check for short circuits */
if ((match && pred->op == OP_OR) ||
(!match && pred->op == OP_AND)) {
if (pred == root)
break;
pred = get_pred_parent(pred, preds,
pred->parent, &move);
continue;
}
/* now go down the right side of the tree. */
pred = &preds[pred->right];
move = MOVE_DOWN;
continue;
case MOVE_UP_FROM_RIGHT:
/* We finished this equation. */
if (pred == root)
break;
pred = get_pred_parent(pred, preds,
pred->parent, &move);
continue;
}
if (pred->pop_n > top) {
WARN_ON_ONCE(1);
return 0;
}
val1 = stack[--top];
val2 = stack[--top];
switch (pred->op) {
case OP_AND:
match = val1 && val2;
break;
case OP_OR:
match = val1 || val2;
break;
default:
WARN_ONCE(1, "filter op is not AND or OR");
}
stack[top++] = match;
}
done = 1;
} while (!done);
return stack[--top];
return match;
}
EXPORT_SYMBOL_GPL(filter_match_preds);
@ -539,10 +587,58 @@ static void filter_clear_pred(struct filter_pred *pred)
pred->regex.len = 0;
}
static int filter_set_pred(struct filter_pred *dest,
static int __alloc_pred_stack(struct pred_stack *stack, int n_preds)
{
stack->preds = kzalloc(sizeof(*stack->preds)*(n_preds + 1), GFP_KERNEL);
if (!stack->preds)
return -ENOMEM;
stack->index = n_preds;
return 0;
}
static void __free_pred_stack(struct pred_stack *stack)
{
kfree(stack->preds);
stack->index = 0;
}
static int __push_pred_stack(struct pred_stack *stack,
struct filter_pred *pred)
{
int index = stack->index;
if (WARN_ON(index == 0))
return -ENOSPC;
stack->preds[--index] = pred;
stack->index = index;
return 0;
}
static struct filter_pred *
__pop_pred_stack(struct pred_stack *stack)
{
struct filter_pred *pred;
int index = stack->index;
pred = stack->preds[index++];
if (!pred)
return NULL;
stack->index = index;
return pred;
}
static int filter_set_pred(struct event_filter *filter,
int idx,
struct pred_stack *stack,
struct filter_pred *src,
filter_pred_fn_t fn)
{
struct filter_pred *dest = &filter->preds[idx];
struct filter_pred *left;
struct filter_pred *right;
*dest = *src;
if (src->field_name) {
dest->field_name = kstrdup(src->field_name, GFP_KERNEL);
@ -550,8 +646,25 @@ static int filter_set_pred(struct filter_pred *dest,
return -ENOMEM;
}
dest->fn = fn;
dest->index = idx;
return 0;
if (dest->op == OP_OR || dest->op == OP_AND) {
right = __pop_pred_stack(stack);
left = __pop_pred_stack(stack);
if (!left || !right)
return -EINVAL;
dest->left = left->index;
dest->right = right->index;
left->parent = dest->index;
right->parent = dest->index | FILTER_PRED_IS_RIGHT;
} else
/*
* Make dest->left invalid to be used as a quick
* way to know this is a leaf node.
*/
dest->left = FILTER_PRED_INVALID;
return __push_pred_stack(stack, dest);
}
static void __free_preds(struct event_filter *filter)
@ -574,6 +687,7 @@ static void reset_preds(struct event_filter *filter)
int i;
filter->n_preds = 0;
filter->root = NULL;
if (!filter->preds)
return;
@ -707,6 +821,7 @@ static int filter_add_pred_fn(struct filter_parse_state *ps,
struct ftrace_event_call *call,
struct event_filter *filter,
struct filter_pred *pred,
struct pred_stack *stack,
filter_pred_fn_t fn)
{
int idx, err;
@ -718,7 +833,7 @@ static int filter_add_pred_fn(struct filter_parse_state *ps,
idx = filter->n_preds;
filter_clear_pred(&filter->preds[idx]);
err = filter_set_pred(&filter->preds[idx], pred, fn);
err = filter_set_pred(filter, idx, stack, pred, fn);
if (err)
return err;
@ -803,6 +918,7 @@ static int filter_add_pred(struct filter_parse_state *ps,
struct ftrace_event_call *call,
struct event_filter *filter,
struct filter_pred *pred,
struct pred_stack *stack,
bool dry_run)
{
struct ftrace_event_field *field;
@ -812,13 +928,10 @@ static int filter_add_pred(struct filter_parse_state *ps,
fn = pred->fn = filter_pred_none;
if (pred->op == OP_AND) {
pred->pop_n = 2;
if (pred->op == OP_AND)
goto add_pred_fn;
} else if (pred->op == OP_OR) {
pred->pop_n = 2;
else if (pred->op == OP_OR)
goto add_pred_fn;
}
field = find_event_field(call, pred->field_name);
if (!field) {
@ -867,7 +980,7 @@ static int filter_add_pred(struct filter_parse_state *ps,
add_pred_fn:
if (!dry_run)
return filter_add_pred_fn(ps, call, filter, pred, fn);
return filter_add_pred_fn(ps, call, filter, pred, stack, fn);
return 0;
}
@ -1248,6 +1361,7 @@ static int replace_preds(struct ftrace_event_call *call,
char *operand1 = NULL, *operand2 = NULL;
struct filter_pred *pred;
struct postfix_elt *elt;
struct pred_stack stack = { }; /* init to NULL */
int err;
int n_preds = 0;
@ -1262,9 +1376,12 @@ static int replace_preds(struct ftrace_event_call *call,
return err;
if (!dry_run) {
err = __alloc_preds(filter, n_preds);
err = __alloc_pred_stack(&stack, n_preds);
if (err)
return err;
err = __alloc_preds(filter, n_preds);
if (err)
goto fail;
}
n_preds = 0;
@ -1276,14 +1393,16 @@ static int replace_preds(struct ftrace_event_call *call,
operand2 = elt->operand;
else {
parse_error(ps, FILT_ERR_TOO_MANY_OPERANDS, 0);
return -EINVAL;
err = -EINVAL;
goto fail;
}
continue;
}
if (WARN_ON(n_preds++ == MAX_FILTER_PRED)) {
parse_error(ps, FILT_ERR_TOO_MANY_PREDS, 0);
return -ENOSPC;
err = -ENOSPC;
goto fail;
}
if (elt->op == OP_AND || elt->op == OP_OR) {
@ -1293,22 +1412,44 @@ static int replace_preds(struct ftrace_event_call *call,
if (!operand1 || !operand2) {
parse_error(ps, FILT_ERR_MISSING_FIELD, 0);
return -EINVAL;
err = -EINVAL;
goto fail;
}
pred = create_pred(elt->op, operand1, operand2);
add_pred:
if (!pred)
return -ENOMEM;
err = filter_add_pred(ps, call, filter, pred, dry_run);
if (!pred) {
err = -ENOMEM;
goto fail;
}
err = filter_add_pred(ps, call, filter, pred, &stack, dry_run);
filter_free_pred(pred);
if (err)
return err;
goto fail;
operand1 = operand2 = NULL;
}
return 0;
if (!dry_run) {
/* We should have one item left on the stack */
pred = __pop_pred_stack(&stack);
if (!pred)
return -EINVAL;
/* This item is where we start from in matching */
filter->root = pred;
/* Make sure the stack is empty */
pred = __pop_pred_stack(&stack);
if (WARN_ON(pred)) {
err = -EINVAL;
filter->root = NULL;
goto fail;
}
}
err = 0;
fail:
__free_pred_stack(&stack);
return err;
}
static int replace_system_preds(struct event_subsystem *system,