Re: [PATCH v2] firmware: arm_sdei: Fix sleep from invalid context BUG

[Pierre Gondois]

The changelog was removed:

v2:
- Don't use a raw spin_lock, but move the CPUHP_AP_ARM_SDEI_
  cpuhp state to the _ONLINE section.


On 10/18/22 15:04, Pierre Gondois wrote:
> On an Ampere Altra,
> Running a preemp_rt kernel based on v5.19-rc3-rt5 on an
> Ampere Altra triggers:
> [   15.683141] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
> [   15.683154] in_atomic(): 0, irqs_disabled(): 128, non_block: 0, pid: 24, name: cpuhp/0
> [   15.683157] preempt_count: 0, expected: 0
> [   15.683159] RCU nest depth: 0, expected: 0
> [   15.683163] 3 locks held by cpuhp/0/24:
> [   15.683167]  #0: ffffda30217c70d0 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0x5c/0x248
> [   15.683201]  #1: ffffda30217c7120 (cpuhp_state-up){+.+.}-{0:0}, at: cpuhp_thread_fun+0x5c/0x248
> [   15.683205]  #2: ffffda3021c711f0 (sdei_list_lock){....}-{3:3}, at: sdei_cpuhp_up+0x3c/0x130
> [   15.683224] irq event stamp: 36
> [   15.683226] hardirqs last  enabled at (35): [<ffffda301e85b7bc>] finish_task_switch+0xb4/0x2b0
> [   15.683236] hardirqs last disabled at (36): [<ffffda301e812fec>] cpuhp_thread_fun+0x21c/0x248
> [   15.683238] softirqs last  enabled at (0): [<ffffda301e80b184>] copy_process+0x63c/0x1ac0
> [   15.683245] softirqs last disabled at (0): [<0000000000000000>] 0x0
> [   15.683258] CPU: 0 PID: 24 Comm: cpuhp/0 Not tainted 5.19.0-rc3-rt5-[...]
> [   15.683265] Hardware name: WIWYNN Mt.Jade Server System B81.03001.0005/Mt.Jade Motherboard, BIOS 1.08.20220218 (SCP: 1.08.20220218) 2022/02/18
> [   15.683268] Call trace:
> [   15.683271]  dump_backtrace+0x114/0x120
> [   15.683277]  show_stack+0x20/0x70
> [   15.683279]  dump_stack_lvl+0x9c/0xd8
> [   15.683288]  dump_stack+0x18/0x34
> [   15.683289]  __might_resched+0x188/0x228
> [   15.683292]  rt_spin_lock+0x70/0x120
> [   15.683301]  sdei_cpuhp_up+0x3c/0x130
> [   15.683303]  cpuhp_invoke_callback+0x250/0xf08
> [   15.683305]  cpuhp_thread_fun+0x120/0x248
> [   15.683308]  smpboot_thread_fn+0x280/0x320
> [   15.683315]  kthread+0x130/0x140
> [   15.683321]  ret_from_fork+0x10/0x20
>
> sdei_cpuhp_up() is called in the STARTING hotplug section,
> which runs whith interrupts disabled. Move CPUHP_AP_ARM_SDEI_
> state to the _ONLINE section to execute the cpuhp cb with
> preemption enabled.
>
> Some SDEI calls (e.g. SDEI_1_0_FN_SDEI_PE_MASK) take actions on the
> calling CPU. It is checked that preemption is disabled for them.
> _ONLINE cpuhp cb are executed in the 'per CPU hotplug thread'.
> Preemption is enabled in those threads, but their cpumask is limited
> to 1 CPU.
> Move 'WARN_ON_ONCE(preemptible())' statements so that SDEI cpuhp cb
> don't trigger them. This means that no check will be done for some
> cases, e.g. sdei_mask_local_cpu() invocations.
>
> Also add a check for the SDEI_1_0_FN_SDEI_PRIVATE_RESET SDEI call
> which acts on the calling CPU.
>
> Suggested-by: James Morse <james.morse@xxxxxxx>
> Signed-off-by: Pierre Gondois <pierre.gondois@xxxxxxx>
> ---
>   drivers/firmware/arm_sdei.c | 28 ++++++++++++++--------------
>   include/linux/cpuhotplug.h  |  2 +-
>   2 files changed, 15 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/firmware/arm_sdei.c b/drivers/firmware/arm_sdei.c
> index 1e1a51510e83..9b03e164a37a 100644
> --- a/drivers/firmware/arm_sdei.c
> +++ b/drivers/firmware/arm_sdei.c
> @@ -301,8 +301,6 @@ int sdei_mask_local_cpu(void)
>   {
>   	int err;
>   
> -	WARN_ON_ONCE(preemptible());
> -
>   	err = invoke_sdei_fn(SDEI_1_0_FN_SDEI_PE_MASK, 0, 0, 0, 0, 0, NULL);
>   	if (err && err != -EIO) {
>   		pr_warn_once("failed to mask CPU[%u]: %d\n",
> @@ -315,6 +313,7 @@ int sdei_mask_local_cpu(void)
>   
>   static void _ipi_mask_cpu(void *ignored)
>   {
> +	WARN_ON_ONCE(preemptible());
>   	sdei_mask_local_cpu();
>   }
>   
> @@ -322,8 +321,6 @@ int sdei_unmask_local_cpu(void)
>   {
>   	int err;
>   
> -	WARN_ON_ONCE(preemptible());
> -
>   	err = invoke_sdei_fn(SDEI_1_0_FN_SDEI_PE_UNMASK, 0, 0, 0, 0, 0, NULL);
>   	if (err && err != -EIO) {
>   		pr_warn_once("failed to unmask CPU[%u]: %d\n",
> @@ -336,6 +333,7 @@ int sdei_unmask_local_cpu(void)
>   
>   static void _ipi_unmask_cpu(void *ignored)
>   {
> +	WARN_ON_ONCE(preemptible());
>   	sdei_unmask_local_cpu();
>   }
>   
> @@ -343,6 +341,8 @@ static void _ipi_private_reset(void *ignored)
>   {
>   	int err;
>   
> +	WARN_ON_ONCE(preemptible());
> +
>   	err = invoke_sdei_fn(SDEI_1_0_FN_SDEI_PRIVATE_RESET, 0, 0, 0, 0, 0,
>   			     NULL);
>   	if (err && err != -EIO)
> @@ -389,8 +389,6 @@ static void _local_event_enable(void *data)
>   	int err;
>   	struct sdei_crosscall_args *arg = data;
>   
> -	WARN_ON_ONCE(preemptible());
> -
>   	err = sdei_api_event_enable(arg->event->event_num);
>   
>   	sdei_cross_call_return(arg, err);
> @@ -401,6 +399,8 @@ int sdei_event_enable(u32 event_num)
>   	int err = -EINVAL;
>   	struct sdei_event *event;
>   
> +	WARN_ON_ONCE(preemptible());
> +
>   	mutex_lock(&sdei_events_lock);
>   	event = sdei_event_find(event_num);
>   	if (!event) {
> @@ -479,8 +479,6 @@ static void _local_event_unregister(void *data)
>   	int err;
>   	struct sdei_crosscall_args *arg = data;
>   
> -	WARN_ON_ONCE(preemptible());
> -
>   	err = sdei_api_event_unregister(arg->event->event_num);
>   
>   	sdei_cross_call_return(arg, err);
> @@ -492,6 +490,7 @@ int sdei_event_unregister(u32 event_num)
>   	struct sdei_event *event;
>   
>   	WARN_ON(in_nmi());
> +	WARN_ON_ONCE(preemptible());
>   
>   	mutex_lock(&sdei_events_lock);
>   	event = sdei_event_find(event_num);
> @@ -561,8 +560,6 @@ static void _local_event_register(void *data)
>   	struct sdei_registered_event *reg;
>   	struct sdei_crosscall_args *arg = data;
>   
> -	WARN_ON(preemptible());
> -
>   	reg = per_cpu_ptr(arg->event->private_registered, smp_processor_id());
>   	err = sdei_api_event_register(arg->event->event_num, sdei_entry_point,
>   				      reg, 0, 0);
> @@ -576,6 +573,7 @@ int sdei_event_register(u32 event_num, sdei_event_callback *cb, void *arg)
>   	struct sdei_event *event;
>   
>   	WARN_ON(in_nmi());
> +	WARN_ON_ONCE(preemptible());
>   
>   	mutex_lock(&sdei_events_lock);
>   	if (sdei_event_find(event_num)) {
> @@ -717,6 +715,8 @@ static int sdei_pm_notifier(struct notifier_block *nb, unsigned long action,
>   {
>   	int rv;
>   
> +	WARN_ON_ONCE(preemptible());
> +
>   	switch (action) {
>   	case CPU_PM_ENTER:
>   		rv = sdei_mask_local_cpu();
> @@ -765,7 +765,7 @@ static int sdei_device_freeze(struct device *dev)
>   	int err;
>   
>   	/* unregister private events */
> -	cpuhp_remove_state(CPUHP_AP_ARM_SDEI_STARTING);
> +	cpuhp_remove_state(CPUHP_AP_ARM_SDEI_ONLINE);
>   
>   	err = sdei_unregister_shared();
>   	if (err)
> @@ -786,7 +786,7 @@ static int sdei_device_thaw(struct device *dev)
>   		return err;
>   	}
>   
> -	err = cpuhp_setup_state(CPUHP_AP_ARM_SDEI_STARTING, "SDEI",
> +	err = cpuhp_setup_state(CPUHP_AP_ARM_SDEI_ONLINE, "SDEI",
>   				&sdei_cpuhp_up, &sdei_cpuhp_down);
>   	if (err)
>   		pr_warn("Failed to re-register CPU hotplug notifier...\n");
> @@ -823,7 +823,7 @@ static int sdei_reboot_notifier(struct notifier_block *nb, unsigned long action,
>   	 * We are going to reset the interface, after this there is no point
>   	 * doing work when we take CPUs offline.
>   	 */
> -	cpuhp_remove_state(CPUHP_AP_ARM_SDEI_STARTING);
> +	cpuhp_remove_state(CPUHP_AP_ARM_SDEI_ONLINE);
>   
>   	sdei_platform_reset();
>   
> @@ -1003,7 +1003,7 @@ static int sdei_probe(struct platform_device *pdev)
>   		goto remove_cpupm;
>   	}
>   
> -	err = cpuhp_setup_state(CPUHP_AP_ARM_SDEI_STARTING, "SDEI",
> +	err = cpuhp_setup_state(CPUHP_AP_ARM_SDEI_ONLINE, "SDEI",
>   				&sdei_cpuhp_up, &sdei_cpuhp_down);
>   	if (err) {
>   		pr_warn("Failed to register CPU hotplug notifier...\n");
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index f61447913db9..63b89e00a4c3 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -161,7 +161,6 @@ enum cpuhp_state {
>   	CPUHP_AP_PERF_X86_CSTATE_STARTING,
>   	CPUHP_AP_PERF_XTENSA_STARTING,
>   	CPUHP_AP_MIPS_OP_LOONGSON3_STARTING,
> -	CPUHP_AP_ARM_SDEI_STARTING,
>   	CPUHP_AP_ARM_VFP_STARTING,
>   	CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
>   	CPUHP_AP_PERF_ARM_HW_BREAKPOINT_STARTING,
> @@ -209,6 +208,7 @@ enum cpuhp_state {
>   	CPUHP_AP_IRQ_AFFINITY_ONLINE,
>   	CPUHP_AP_BLK_MQ_ONLINE,
>   	CPUHP_AP_ARM_MVEBU_SYNC_CLOCKS,
> +	CPUHP_AP_ARM_SDEI_ONLINE,
>   	CPUHP_AP_X86_INTEL_EPB_ONLINE,
>   	CPUHP_AP_PERF_ONLINE,
>   	CPUHP_AP_PERF_X86_ONLINE,