tracing/ftrace: fix unexpected -EINVAL when longest tracer name is set

Impact: fix confusing write() -EINVAL when changing the tracer

The following commit d9e540762f5cdd89f24e518ad1fd31142d0b9726 remade
alive the bug which made the set of a new tracer returning -EINVAL if
this is the longest name of tracer. This patch corrects it.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 5 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index dff4bee591b9..80898f4870cc 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2655,6 +2655,9 @@ tracing_set_trace_write(struct file *filp, const char __user *ubuf,
         char buf[max_tracer_type_len+1];
         int i;
         size_t ret;
+        int err;
+
+        ret = cnt;
 
         if (cnt > max_tracer_type_len)
                 cnt = max_tracer_type_len;
@@ -2668,12 +2671,11 @@ tracing_set_trace_write(struct file *filp, const char __user *ubuf,
         for (i = cnt - 1; i > 0 && isspace(buf[i]); i--)
                 buf[i] = 0;
 
-        ret = tracing_set_tracer(buf);
-        if (!ret)
-                ret = cnt;
+        err = tracing_set_tracer(buf);
+        if (err)
+                return err;
 
-        if (ret > 0)
-                filp->f_pos += ret;
+        filp->f_pos += ret;
 
         return ret;
 }