Re: [PATCH 1/2] tracing: Do not initialize tracefs work if tracing is disabled

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Fri, 09 Oct 2026 22:05:56 +0530, Amit Machhiwal <amachhiw@linux.ibm.com> wrote:
> If trace buffer allocation fails during early boot (e.g.  in
> early_trace_init() -> allocate_trace_buffers()), tracing_disabled is
> left set to 1 and the global trace array events list remains
> uninitialized.
>
> Later during boot, tracer_init_tracefs() (invoked via fs_initcall)
> queues tracerfs_init_work asynchronously without checking if tracing was
> disabled.  When tracer_init_tracefs_work_func() runs, it calls
> event_trace_init() and init_tracer_tracefs(&global_trace, NULL)
> unconditionally.  This leads to __find_event_file() dereferencing an
> uninitialized tr->events list, causing an early boot NULL pointer
> dereference Oops:
>
>   BUG: Kernel NULL pointer dereference on read at 0x00000010
>   Faulting instruction address: 0xc000000000485be0
>   Oops: Kernel access of bad area, sig: 7 [#1]
>   ...
>   NIP [c000000000485be0] __find_event_file+0x70/0x3c0
>   LR  [c000000000448874] init_tracer_tracefs+0x274/0xc80
>   Call Trace:
>    init_tracer_tracefs+0x274/0xc80
>    tracer_init_tracefs_work_func+0x50/0x320
>    process_one_work+0x1e8/0x5c0
>    worker_thread+0x1dc/0x3d0
>    kthread+0x194/0x1b0
>    start_kernel_thread+0x14/0x18
>
> Check tracing_disabled at the beginning of tracer_init_tracefs_work_func()
> and return immediately if tracing is disabled or failed to initialize,
> preventing the crash.
>

Looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

> Fixes: 6621a7004684 ("tracing: make tracer_init_tracefs initcall asynchronous")
> Cc: stable@vger.kernel.org
> Reported-by: Michal Suchánek <msuchanek@suse.de>
> Closes: https://lore.kernel.org/all/arYskzbiaNzBR9MD@kunlun.suse.cz/
> Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>
> ---
>  kernel/trace/trace.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index e4a490d3d08c..7ac9e1c92702 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -9287,6 +9287,12 @@ static struct notifier_block trace_module_nb = {
>  
>  static __init void tracer_init_tracefs_work_func(struct work_struct *work)
>  {
> +	/*
> +	 * Do not attempt to initialize tracefs if tracing was disabled or
> +	 * failed to allocate
> +	 */
> +	if (tracing_disabled)
> +		return;
>  
>  	event_trace_init();
>  
> -- 
> 2.54.0 (Apple Git-157)
>

Thanks!

-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>