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>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index dff4bee..80898f4 100644 (file)
--- 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;
 }