ftrace: return an error when setting a nonexistent tracer

When one try to set a nonexistent tracer, no error is returned
as if the name of the tracer was correct.
We should return -EINVAL.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 3 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index caa4051ce778..78d56614c95b 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2381,9 +2381,11 @@ tracing_set_trace_write(struct file *filp, const char __user *ubuf,
         struct tracer *t;
         char buf[max_tracer_type_len+1];
         int i;
+        size_t ret;
 
         if (cnt > max_tracer_type_len)
                 cnt = max_tracer_type_len;
+        ret = cnt;
 
         if (copy_from_user(&buf, ubuf, cnt))
                 return -EFAULT;
@@ -2399,7 +2401,11 @@ tracing_set_trace_write(struct file *filp, const char __user *ubuf,
                 if (strcmp(t->name, buf) == 0)
                         break;
         }
-        if (!t || t == current_trace)
+        if (!t) {
+                ret = -EINVAL;
+                goto out;
+        }
+        if (t == current_trace)
                 goto out;
 
         if (current_trace && current_trace->reset)
@@ -2412,9 +2418,10 @@ tracing_set_trace_write(struct file *filp, const char __user *ubuf,
  out:
         mutex_unlock(&trace_types_lock);
 
-        filp->f_pos += cnt;
+        if (ret == cnt)
+                filp->f_pos += cnt;
 
-        return cnt;
+        return ret;
 }
 
 static ssize_t