When current namespace is not the global namespace,
pid read from set_ftrace_pid is no correct.

# ~/newpid_namespace_run bash
# echo $$
1
# echo 1 > set_ftrace_pid
# cat set_ftrace_pid
3756

Since we write virtual PID to set_ftrace_pid, we need get
virtual PID when we read it.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 7847806..7d7f201 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2262,7 +2262,7 @@ ftrace_pid_read(struct file *file, char __user *ubuf,
 	if (ftrace_pid_trace == ftrace_swapper_pid)
 		r = sprintf(buf, "swapper tasks\n");
 	else if (ftrace_pid_trace)
-		r = sprintf(buf, "%u\n", pid_nr(ftrace_pid_trace));
+		r = sprintf(buf, "%u\n", pid_vnr(ftrace_pid_trace));
 	else
 		r = sprintf(buf, "no pid\n");
 

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