Re: [PATCH v10 4/9] drivers: firmware: add riscv SSE support

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] lockdep_assert_preemption_disabled() in local event functions triggers a lockdep splat when called from CPU hotplug callbacks.
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commit c8e18c554b3059a878f2a5763162d36f8061a2de
Author: Clément Léger <cleger@rivosinc.com>
drivers: firmware: add riscv SSE support

This commit adds a driver-level interface for RISC-V Supervisor Software
Events (SSE). It allows Linux clients to register NMI-like event handlers,
select target CPUs, and manage global or local events while handling CPU 
hotplug and firmware interactions.

> diff --git a/drivers/firmware/riscv/riscv_sbi_sse.c b/drivers/firmware/riscv/riscv_sbi_sse.c
> new file mode 100644
> index 0000000000000..e81cfb4b0c563
> --- /dev/null
> +++ b/drivers/firmware/riscv/riscv_sbi_sse.c

[ ... ]

> +int sse_event_disable_local(struct sse_event *event)
> +{
> +	if (!sse_event_is_global(event->evt_id))
> +		lockdep_assert_preemption_disabled();
> +
> +	if (!sse_get_reg_evt(event)->is_enabled)
> +		return 0;
> +
> +	return sse_sbi_event_func(event, SBI_SSE_EVENT_DISABLE);
> +}
> +EXPORT_SYMBOL_GPL(sse_event_disable_local);
> +
> +int sse_event_enable_local(struct sse_event *event)
> +{
> +	struct sse_registered_event *reg_evt = sse_get_reg_evt(event);
> +	int ret;
> +
> +	if (!sse_event_is_global(event->evt_id))
> +		lockdep_assert_preemption_disabled();

[ ... ]

> +static int sse_cpu_online(unsigned int cpu)
> +{
> +	int ret, rollback_ret;
> +	struct sse_event *event, *tmp;
> +	struct sse_registered_event *reg_evt;
> +
> +	arch_sse_init_cpu();
> +
> +	list_for_each_entry_safe(event, tmp, &events, list) {
> +		if (sse_event_is_global(event->evt_id))
> +			continue;
> +		if (event->cleanup_pending) {
> +			ret = sse_teardown_event(event, cpu);
> +			if (ret)
> +				goto rollback;
> +			sse_release_cleanup_event(event);
> +			continue;
> +		}
> +
> +		ret = sse_event_register_local(event);
> +		if (ret)
> +			goto rollback;
> +		if (event->enable_requested)
> +			ret = sse_event_enable_local(event);
> +		else
> +			ret = sse_event_disable_local(event);

[Severity: Medium]
Will this lockdep assertion trigger a warning during CPU hotplug operations?

The CPU hotplug callback sse_cpu_online() (as well as sse_cpu_teardown() via 
sse_teardown_event()) runs from the hotplug thread with preemption enabled. 

When these callbacks process local events, they directly invoke 
sse_event_enable_local() and sse_event_disable_local(). Because those 
functions enforce lockdep_assert_preemption_disabled() for local events, 
could this cause a lockdep splat whenever a CPU is brought online or offline?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260911121456.33223-1-zhangzhanpeng.jasper@bytedance.com?part=4