[PATCH 3/5] tracing/ftrace: check if debugfs is registered before creating files

[Frederic Weisbecker]

Impact: fix a crash with ftrace={nop,boot} parameter

If the nop or initcall tracers are launched as boot tracers,
they will attempt to create their option directory and files.
But these tracers are registered very early and then assigned
as "boot tracers" very early if asked to.

Since they do this before debugfs has been registered (core initcall),
a crash is triggered.

Another early tracers could also come later. So we fix it by
checking if debugfs is initialized before creating the root
tracing directory.

Cc: Greg Kroah-Hartman <gregkh@xxxxxxx>
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
---
 kernel/trace/trace.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ace685c..f0e1337 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3513,6 +3513,9 @@ struct dentry *tracing_init_dentry(void)
 	if (d_tracer)
 		return d_tracer;
 
+	if (!debugfs_initialized())
+		return NULL;
+
 	d_tracer = debugfs_create_dir("tracing", NULL);
 
 	if (!d_tracer && !once) {
-- 
1.6.1

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