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

[Pierre Gondois <pierre.gondois@arm.com>]

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@arm.com>
Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
---
 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,
-- 
2.25.1