[RFC PATCH v2 02/20] tracing/filters: Enable filtering a cpumask field by another cpumask

Valentin Schneider
2023-07-20T16:33:26Z

The recently introduced ipi_send_cpumask trace event contains a cpumask
field, but it currently cannot be used in filter expressions.

Make event filtering aware of cpumask fields, and allow these to be
filtered by a user-provided cpumask.

The user-provided cpumask is to be given in cpulist format and wrapped as:
"CPUS{$cpulist}". The use of curly braces instead of parentheses is to
prevent predicate_parse() from parsing the contents of CPUS{...} as a
full-fledged predicate subexpression.

This enables e.g.:

$ trace-cmd record -e 'ipi_send_cpumask' -f 'cpumask & CPUS{2,4,6,8-32}'

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
---
include/linux/trace_events.h | 1 +
kernel/trace/trace_events_filter.c | 97 +++++++++++++++++++++++++++++-
2 files changed, 96 insertions(+), 2 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 3930e676436c9..302be73918336 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -807,6 +807,7 @@ enum {
FILTER_RDYN_STRING,
FILTER_PTR_STRING,
FILTER_TRACE_FN,
+ FILTER_CPUMASK,
FILTER_COMM,
FILTER_CPU,
FILTER_STACKTRACE,
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 91fc9990107f1..cb1863dfa280b 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -64,6 +64,7 @@ enum filter_pred_fn {
FILTER_PRED_FN_PCHAR_USER,
FILTER_PRED_FN_PCHAR,
FILTER_PRED_FN_CPU,
+ FILTER_PRED_FN_CPUMASK,
FILTER_PRED_FN_FUNCTION,
FILTER_PRED_FN_,
FILTER_PRED_TEST_VISITED,
@@ -71,6 +72,7 @@ enum filter_pred_fn {

struct filter_pred {
struct regex *regex;
+ struct cpumask *mask;
unsigned short *ops;
struct ftrace_event_field *field;
u64 val;
@@ -94,6 +96,8 @@ struct filter_pred {
C(TOO_MANY_OPEN, "Too many '('"), \
C(TOO_MANY_CLOSE, "Too few '('"), \
C(MISSING_QUOTE, "Missing matching quote"), \
+ C(MISSING_BRACE_OPEN, "Missing '{'"), \
+ C(MISSING_BRACE_CLOSE, "Missing '}'"), \
C(OPERAND_TOO_LONG, "Operand too long"), \
C(EXPECT_STRING, "Expecting string field"), \
C(EXPECT_DIGIT, "Expecting numeric field"), \
@@ -103,6 +107,7 @@ struct filter_pred {
C(BAD_SUBSYS_FILTER, "Couldn't find or set field in one of a subsystem's events"), \
C(TOO_MANY_PREDS, "Too many terms in predicate expression"), \
C(INVALID_FILTER, "Meaningless filter expression"), \
+ C(INVALID_CPULIST, "Invalid cpulist"), \
C(IP_FIELD_ONLY, "Only 'ip' field is supported for function trace"), \
C(INVALID_VALUE, "Invalid value (did you forget quotes)?"), \
C(NO_FUNCTION, "Function not found"), \
@@ -190,6 +195,7 @@ static void free_predicate(struct filter_pred *pred)
{
if (pred) {
kfree(pred->regex);
+ kfree(pred->mask);
kfree(pred);
}
}
@@ -877,6 +883,26 @@ static int filter_pred_cpu(struct filter_pred *pred, void *event)
}
}

+/* Filter predicate for cpumask field vs user-provided cpumask */
+static int filter_pred_cpumask(struct filter_pred *pred, void *event)
+{
+ u32 item = *(u32 *)(event + pred->offset);
+ int loc = item & 0xffff;
+ const struct cpumask *mask = (event + loc);
+ const struct cpumask *cmp = pred->mask;
+
+ switch (pred->op) {
+ case OP_EQ:
+ return cpumask_equal(mask, cmp);
+ case OP_NE:
+ return !cpumask_equal(mask, cmp);
+ case OP_BAND:
+ return cpumask_intersects(mask, cmp);
+ default:
+ return 0;
+ }
+}
+
/* Filter predicate for COMM. */
static int filter_pred_comm(struct filter_pred *pred, void *event)
{
@@ -1244,8 +1270,12 @@ static void filter_free_subsystem_filters(struct trace_subsystem_dir *dir,

int filter_assign_type(const char *type)
{
- if (strstr(type, "__data_loc") && strstr(type, "char"))
- return FILTER_DYN_STRING;
+ if (strstr(type, "__data_loc")) {
+ if (strstr(type, "char"))
+ return FILTER_DYN_STRING;
+ if (strstr(type, "cpumask_t"))
+ return FILTER_CPUMASK;
+ }

if (strstr(type, "__rel_loc") && strstr(type, "char"))
return FILTER_RDYN_STRING;
@@ -1357,6 +1387,8 @@ static int filter_pred_fn_call(struct filter_pred *pred, void *event)
return filter_pred_pchar(pred, event);
case FILTER_PRED_FN_CPU:
return filter_pred_cpu(pred, event);
+ case FILTER_PRED_FN_CPUMASK:
+ return filter_pred_cpumask(pred, event);
case FILTER_PRED_FN_FUNCTION:
return filter_pred_function(pred, event);
case FILTER_PRED_TEST_VISITED:
@@ -1568,6 +1600,67 @@ static int parse_pred(const char *str, void *data,
strncpy(pred->regex->pattern, str + s, len);
pred->regex->pattern[len] = 0;

+ } else if (!strncmp(str + i, "CPUS", 4)) {
+ unsigned int maskstart;
+ char *tmp;
+
+ switch (field->filter_type) {
+ case FILTER_CPUMASK:
+ break;
+ default:
+ parse_error(pe, FILT_ERR_ILLEGAL_FIELD_OP, pos + i);
+ goto err_free;
+ }
+
+ switch (op) {
+ case OP_EQ:
+ case OP_NE:
+ case OP_BAND:
+ break;
+ default:
+ parse_error(pe, FILT_ERR_ILLEGAL_FIELD_OP, pos + i);
+ goto err_free;
+ }
+
+ /* Skip CPUS */
+ i += 4;
+ if (str[i++] != '{') {
+ parse_error(pe, FILT_ERR_MISSING_BRACE_OPEN, pos + i);
+ goto err_free;
+ }
+ maskstart = i;
+
+ /* Walk the cpulist until closing } */
+ for (; str[i] && str[i] != '}'; i++);
+ if (str[i] != '}') {
+ parse_error(pe, FILT_ERR_MISSING_BRACE_CLOSE, pos + i);
+ goto err_free;
+ }
+
+ if (maskstart == i) {
+ parse_error(pe, FILT_ERR_INVALID_CPULIST, pos + i);
+ goto err_free;
+ }
+
+ /* Copy the cpulist between { and } */
+ tmp = kmalloc((i - maskstart) + 1, GFP_KERNEL);
+ strscpy(tmp, str + maskstart, (i - maskstart) + 1);
+
+ pred->mask = kzalloc(cpumask_size(), GFP_KERNEL);
+ if (!pred->mask)
+ goto err_mem;
+
+ /* Now parse it */
+ if (cpulist_parse(tmp, pred->mask)) {
+ parse_error(pe, FILT_ERR_INVALID_CPULIST, pos + i);
+ goto err_free;
+ }
+
+ /* Move along */
+ i++;
+ if (field->filter_type == FILTER_CPUMASK)
+ pred->fn_num = FILTER_PRED_FN_CPUMASK;
+
/* This is either a string, or an integer */
} else if (str[i] == '\'' || str[i] == '"') {
char q = str[i];
--
2.31.1