ftrace: Do not copy hash if O_TRUNC is set

When a filter file is open for writing and O_TRUNC is set, there's no
need to copy and free the filter entries.

Link: http://lkml.kernel.org/p/1402474014-28655-2-git-send-email-namhyung@kernel.org

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 7 insertions, 5 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index e14ff4c1713e..232b898eebbd 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3010,7 +3010,13 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
                 hash = ops->filter_hash;
 
         if (file->f_mode & FMODE_WRITE) {
-                iter->hash = alloc_and_copy_ftrace_hash(FTRACE_HASH_DEFAULT_BITS, hash);
+                const int size_bits = FTRACE_HASH_DEFAULT_BITS;
+
+                if (file->f_flags & O_TRUNC)
+                        iter->hash = alloc_ftrace_hash(size_bits);
+                else
+                        iter->hash = alloc_and_copy_ftrace_hash(size_bits, hash);
+
                 if (!iter->hash) {
                         trace_parser_put(&iter->parser);
                         kfree(iter);
@@ -3019,10 +3025,6 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
                 }
         }
 
-        if ((file->f_mode & FMODE_WRITE) &&
-            (file->f_flags & O_TRUNC))
-                ftrace_filter_reset(iter->hash);
-
         if (file->f_mode & FMODE_READ) {
                 iter->pg = ftrace_pages_start;