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

On Sun, 22 Mar 2009, Frederic Weisbecker wrote:

> 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@suse.de>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> ---
> 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);
>

Hmm, those tracers should separate out the debugfs code, and put it into
a fs_initcall(), where debugfs should already initialized.

-- Steve



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