trace: judicious error checking of trace_seq results

Impact: bugfix and cleanup

Some callsites were returning either TRACE_ITER_PARTIAL_LINE if the
trace_seq routines (trace_seq_printf, etc) returned 0 meaning its buffer
was full, or zero otherwise.

But...

/* Return values for print_line callback */
enum print_line_t {
        TRACE_TYPE_PARTIAL_LINE = 0,    /* Retry after flushing the seq */
        TRACE_TYPE_HANDLED      = 1,
        TRACE_TYPE_UNHANDLED    = 2     /* Relay to other output functions */
};

In other cases the return value was not being relayed at all.

Most of the time it didn't hurt because the page wasn't get filled, but
for correctness sake, handle the return values everywhere.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

block/blktrace.c

@@ -1165,7 +1165,7 @@ static int blk_trace_event_print(struct trace_iterator *iter, int flags)
 	const u16 what = t->action & ((1 << BLK_TC_SHIFT) - 1);
 	int ret;
 
-	if (trace_print_context(iter))
+	if (!trace_print_context(iter))
 		return TRACE_TYPE_PARTIAL_LINE;
 
 	if (unlikely(what == 0 || what > ARRAY_SIZE(what2act)))

kernel/trace/trace.c

@@ -1402,27 +1402,25 @@ static enum print_line_t print_lat_fmt(struct trace_iterator *iter)
 	unsigned long sym_flags = (trace_flags & TRACE_ITER_SYM_MASK);
 	struct trace_event *event;
 	struct trace_entry *entry = iter->ent;
-	int ret;
 
 	test_cpu_buff_start(iter);
 
 	event = ftrace_find_event(entry->type);
 
 	if (trace_flags & TRACE_ITER_CONTEXT_INFO) {
-		ret = trace_print_lat_context(iter);
-		if (ret)
-			return ret;
+		if (!trace_print_lat_context(iter))
+			goto partial;
 	}
 
-	if (event && event->latency_trace) {
-		ret = event->latency_trace(iter, sym_flags);
-		if (ret)
-			return ret;
-		return TRACE_TYPE_HANDLED;
-	}
+	if (event && event->latency_trace)
+		return event->latency_trace(iter, sym_flags);
+
+	if (!trace_seq_printf(s, "Unknown type %d\n", entry->type))
+		goto partial;
 
-	trace_seq_printf(s, "Unknown type %d\n", entry->type);
 	return TRACE_TYPE_HANDLED;
+partial:
+	return TRACE_TYPE_PARTIAL_LINE;
 }
 
 static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
@@ -1431,7 +1429,6 @@ static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
 	unsigned long sym_flags = (trace_flags & TRACE_ITER_SYM_MASK);
 	struct trace_entry *entry;
 	struct trace_event *event;
-	int ret;
 
 	entry = iter->ent;
 
@@ -1440,52 +1437,45 @@ static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
 	event = ftrace_find_event(entry->type);
 
 	if (trace_flags & TRACE_ITER_CONTEXT_INFO) {
-		ret = trace_print_context(iter);
-		if (ret)
-			return ret;
+		if (!trace_print_context(iter))
+			goto partial;
 	}
 
-	if (event && event->trace) {
-		ret = event->trace(iter, sym_flags);
-		if (ret)
-			return ret;
-		return TRACE_TYPE_HANDLED;
-	}
-	ret = trace_seq_printf(s, "Unknown type %d\n", entry->type);
-	if (!ret)
-		return TRACE_TYPE_PARTIAL_LINE;
+	if (event && event->trace)
+		return event->trace(iter, sym_flags);
+
+	if (!trace_seq_printf(s, "Unknown type %d\n", entry->type))
+		goto partial;
 
 	return TRACE_TYPE_HANDLED;
+partial:
+	return TRACE_TYPE_PARTIAL_LINE;
 }
 
 static enum print_line_t print_raw_fmt(struct trace_iterator *iter)
 {
 	struct trace_seq *s = &iter->seq;
 	struct trace_entry *entry;
 	struct trace_event *event;
-	int ret;
 
 	entry = iter->ent;
 
 	if (trace_flags & TRACE_ITER_CONTEXT_INFO) {
-		ret = trace_seq_printf(s, "%d %d %llu ",
-			entry->pid, iter->cpu, iter->ts);
-		if (!ret)
-			return TRACE_TYPE_PARTIAL_LINE;
+		if (!trace_seq_printf(s, "%d %d %llu ",
+				      entry->pid, iter->cpu, iter->ts))
+			goto partial;
 	}
 
 	event = ftrace_find_event(entry->type);
-	if (event && event->raw) {
-		ret = event->raw(iter, 0);
-		if (ret)
-			return ret;
-		return TRACE_TYPE_HANDLED;
-	}
-	ret = trace_seq_printf(s, "%d ?\n", entry->type);
-	if (!ret)
-		return TRACE_TYPE_PARTIAL_LINE;
+	if (event && event->raw)
+		return event->raw(iter, 0);
+
+	if (!trace_seq_printf(s, "%d ?\n", entry->type))
+		goto partial;
 
 	return TRACE_TYPE_HANDLED;
+partial:
+	return TRACE_TYPE_PARTIAL_LINE;
 }
 
 static enum print_line_t print_hex_fmt(struct trace_iterator *iter)
@@ -1504,8 +1494,11 @@ static enum print_line_t print_hex_fmt(struct trace_iterator *iter)
 	}
 
 	event = ftrace_find_event(entry->type);
-	if (event && event->hex)
-		event->hex(iter, 0);
+	if (event && event->hex) {
+		int ret = event->hex(iter, 0);
+		if (ret != TRACE_TYPE_HANDLED)
+			return ret;
+	}
 
 	SEQ_PUT_FIELD_RET(s, newline);
 
@@ -1544,7 +1537,7 @@ static enum print_line_t print_bin_fmt(struct trace_iterator *iter)
 
 	event = ftrace_find_event(entry->type);
 	if (event && event->binary)
-		event->binary(iter, 0);
+		return event->binary(iter, 0);
 
 	return TRACE_TYPE_HANDLED;
 }

kernel/trace/trace_branch.c

@@ -173,7 +173,7 @@ static int trace_branch_print(struct trace_iterator *iter, int flags)
 			     field->line))
 		return TRACE_TYPE_PARTIAL_LINE;
 
-	return 0;
+	return TRACE_TYPE_HANDLED;
 }