fault-injection: skip stacktrace filtering by default

If FAULT_INJECTION_STACKTRACE_FILTER is enabled, the depth is default to
32.  This means fail_stacktrace() will iter each entry's stacktrace, even
if filter is not configured.

This patch changes to quick return from fail_stacktrace() if stacktrace
filter is not set.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Wei Yongjun <[email protected]>
Cc: Akinobu Mita <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Isabella Basso <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Wei Yongjun

lib/fault-inject.c

@@ -71,7 +71,7 @@ static bool fail_stacktrace(struct fault_attr *attr)
 	int n, nr_entries;
 	bool found = (attr->require_start == 0 && attr->require_end == ULONG_MAX);
 
-	if (depth == 0)
+	if (depth == 0 || (found && !attr->reject_start && !attr->reject_end))
 		return found;
 
 	nr_entries = stack_trace_save(entries, depth, 1);