Re: [PATCH 1/3] kernel/reboot: Use the static sys-off handler for any priority

[Palmer Dabbelt]

On Wed, 28 Dec 2022 08:19:13 PST (-0800), samuel@xxxxxxxxxxxx wrote:
> commit 587b9bfe0668 ("kernel/reboot: Use static handler for
> register_platform_power_off()") addded a statically-allocated handler
> so register_sys_off_handler() could be called before the slab allocator
> is available.
>
> That behavior was limited to the SYS_OFF_PRIO_PLATFORM priority.
> However, it is also required for handlers such as PSCI on ARM and SBI on
> RISC-V, which should be registered at SYS_OFF_PRIO_FIRMWARE. Currently,
> this call stack crashes:
>
>   start_kernel()
>     setup_arch()
>       psci_dt_init()
>         psci_0_2_init()
>           register_sys_off_handler()
>             kmem_cache_alloc()
>
> Generalize the code to use the statically-allocated handler for the
> first registration, regardless of priority. Check .sys_off_cb for
> conflicts instead of .cb_data; some callbacks (e.g. firmware drivers)
> do not need any per-instance data, so .cb_data could be NULL.
>
> Reviewed-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
> Signed-off-by: Samuel Holland <samuel@xxxxxxxxxxxx>
> ---
>
>  kernel/reboot.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/reboot.c b/kernel/reboot.c
> index 3bba88c7ffc6..38c18d4f0a36 100644
> --- a/kernel/reboot.c
> +++ b/kernel/reboot.c
> @@ -327,7 +327,7 @@ static int sys_off_notify(struct notifier_block *nb,
>  	return handler->sys_off_cb(&data);
>  }
>
> -static struct sys_off_handler platform_sys_off_handler;
> +static struct sys_off_handler early_sys_off_handler;
>
>  static struct sys_off_handler *alloc_sys_off_handler(int priority)
>  {
> @@ -338,10 +338,8 @@ static struct sys_off_handler *alloc_sys_off_handler(int priority)
>  	 * Platforms like m68k can't allocate sys_off handler dynamically
>  	 * at the early boot time because memory allocator isn't available yet.
>  	 */
> -	if (priority == SYS_OFF_PRIO_PLATFORM) {
> -		handler = &platform_sys_off_handler;
> -		if (handler->cb_data)
> -			return ERR_PTR(-EBUSY);
> +	if (!early_sys_off_handler.sys_off_cb) {
> +		handler = &early_sys_off_handler;
>  	} else {
>  		if (system_state > SYSTEM_RUNNING)
>  			flags = GFP_ATOMIC;
> @@ -358,7 +356,7 @@ static struct sys_off_handler *alloc_sys_off_handler(int priority)
>
>  static void free_sys_off_handler(struct sys_off_handler *handler)
>  {
> -	if (handler == &platform_sys_off_handler)
> +	if (handler == &early_sys_off_handler)
>  		memset(handler, 0, sizeof(*handler));
>  	else
>  		kfree(handler);

Sorry for being slow here, I'd been assuming someone would Ack this but 
it looks like maybe there's nobody in the maintainers file for 
kernel/reboot.c?  I'm fine taking this via the RISC-V tree if that's OK 
with people, but the cover letter suggests the patch is necessary for 
multiple patch sets.