perf lock contention: Factor out lock_contention_get_name()

The lock_contention_get_name() returns a name for the lock stat entry
based on the current aggregation mode.  As it's called sequentially in a
single thread, it can return the address of a static buffer for symbol
and offset of the caller.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Hao Luo <haoluo@google.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <song@kernel.org>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20230203021324.143540-2-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: namhyung

tools/perf/util/bpf_lock_contention.c

@@ -163,9 +163,70 @@ int lock_contention_stop(void)
 	return 0;
 }
 
+static const char *lock_contention_get_name(struct lock_contention *con,
+					    struct contention_key *key,
+					    u64 *stack_trace)
+{
+	int idx = 0;
+	u64 addr;
+	const char *name = "";
+	static char name_buf[KSYM_NAME_LEN];
+	struct symbol *sym;
+	struct map *kmap;
+	struct machine *machine = con->machine;
+
+	if (con->aggr_mode == LOCK_AGGR_TASK) {
+		struct contention_task_data task;
+		int pid = key->aggr_key;
+		int task_fd = bpf_map__fd(skel->maps.task_data);
+
+		/* do not update idle comm which contains CPU number */
+		if (pid) {
+			struct thread *t = __machine__findnew_thread(machine, /*pid=*/-1, pid);
+
+			if (t == NULL)
+				return name;
+			if (!bpf_map_lookup_elem(task_fd, &pid, &task) &&
+			    thread__set_comm(t, task.comm, /*timestamp=*/0))
+				name = task.comm;
+		}
+		return name;
+	}
+
+	if (con->aggr_mode == LOCK_AGGR_ADDR) {
+		sym = machine__find_kernel_symbol(machine, key->aggr_key, &kmap);
+		if (sym)
+			name = sym->name;
+		return name;
+	}
+
+	/* LOCK_AGGR_CALLER: skip lock internal functions */
+	while (machine__is_lock_function(machine, stack_trace[idx]) &&
+	       idx < con->max_stack - 1)
+		idx++;
+
+	addr = stack_trace[idx];
+	sym = machine__find_kernel_symbol(machine, addr, &kmap);
+
+	if (sym) {
+		unsigned long offset;
+
+		offset = kmap->map_ip(kmap, addr) - sym->start;
+
+		if (offset == 0)
+			return sym->name;
+
+		snprintf(name_buf, sizeof(name_buf), "%s+%#lx", sym->name, offset);
+	} else {
+		snprintf(name_buf, sizeof(name_buf), "%#lx", (unsigned long)addr);
+	}
+
+	return name_buf;
+}
+
 int lock_contention_read(struct lock_contention *con)
 {
-	int fd, stack, task_fd, err = 0;
+	int fd, stack, err = 0;
 	struct contention_key *prev_key, key;
 	struct contention_data data = {};
 	struct lock_stat *st = NULL;
@@ -175,7 +236,6 @@ int lock_contention_read(struct lock_contention *con)
 
 	fd = bpf_map__fd(skel->maps.lock_stat);
 	stack = bpf_map__fd(skel->maps.stacks);
-	task_fd = bpf_map__fd(skel->maps.task_data);
 
 	con->lost = skel->bss->lost;
 
@@ -195,9 +255,6 @@ int lock_contention_read(struct lock_contention *con)
 
 	prev_key = NULL;
 	while (!bpf_map_get_next_key(fd, prev_key, &key)) {
-		struct map *kmap;
-		struct symbol *sym;
-		int idx = 0;
 		s32 stack_id;
 
 		/* to handle errors in the loop body */
@@ -219,61 +276,19 @@ int lock_contention_read(struct lock_contention *con)
 		st->flags = data.flags;
 		st->addr = key.aggr_key;
 
-		if (con->aggr_mode == LOCK_AGGR_TASK) {
-			struct contention_task_data task;
-			struct thread *t;
-			int pid = key.aggr_key;
-
-			/* do not update idle comm which contains CPU number */
-			if (st->addr) {
-				bpf_map_lookup_elem(task_fd, &pid, &task);
-				t = __machine__findnew_thread(machine, /*pid=*/-1, pid);
-				thread__set_comm(t, task.comm, /*timestamp=*/0);
-			}
-			goto next;
-		}
-
-		if (con->aggr_mode == LOCK_AGGR_ADDR) {
-			sym = machine__find_kernel_symbol(machine, st->addr, &kmap);
-			if (sym)
-				st->name = strdup(sym->name);
-			goto next;
-		}
-
 		stack_id = key.aggr_key;
 		bpf_map_lookup_elem(stack, &stack_id, stack_trace);
 
-		/* skip lock internal functions */
-		while (machine__is_lock_function(machine, stack_trace[idx]) &&
-		       idx < con->max_stack - 1)
-			idx++;
-
-		st->addr = stack_trace[idx];
-		sym = machine__find_kernel_symbol(machine, st->addr, &kmap);
-
-		if (sym) {
-			unsigned long offset;
-			int ret = 0;
-
-			offset = kmap->map_ip(kmap, st->addr) - sym->start;
-
-			if (offset)
-				ret = asprintf(&st->name, "%s+%#lx", sym->name, offset);
-			else
-				st->name = strdup(sym->name);
-
-			if (ret < 0 || st->name == NULL)
-				break;
-		} else if (asprintf(&st->name, "%#lx", (unsigned long)st->addr) < 0) {
+		st->name = strdup(lock_contention_get_name(con, &key, stack_trace));
+		if (st->name == NULL)
 			break;
-		}
 
 		if (con->save_callstack) {
 			st->callstack = memdup(stack_trace, stack_size);
 			if (st->callstack == NULL)
 				break;
 		}
-next:
+
 		hlist_add_head(&st->hash_entry, con->result);
 		prev_key = &key;