tracing/ftrace: check if debugfs is registered before creating files

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.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1237759847-21025-3-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ace685c7018668b58a5b035c5cf7f9b738d555d5..f0e1337b1ebd5481dc2d6fdd4a1e1429f36de8d4 100644 (file)
--- 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) {