[PATCH v4] firmware: arm_sdei: Fix sleep from invalid context BUG

From: Pierre Gondois
Date: Thu Feb 16 2023 - 03:49:30 EST

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Running a preemp_rt kernel based on vv6.2-rc3-rt1 based kernel on an
Ampere Altra triggers:
BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
in_atomic(): 0, irqs_disabled(): 128, non_block: 0, pid: 24, name: cpuhp/0
preempt_count: 0, expected: 0
RCU nest depth: 0, expected: 0
3 locks held by cpuhp/0/24:
#0: ffffda30217c70d0 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0x5c/0x248
#1: ffffda30217c7120 (cpuhp_state-up){+.+.}-{0:0}, at: cpuhp_thread_fun+0x5c/0x248
#2: ffffda3021c711f0 (sdei_list_lock){....}-{3:3}, at: sdei_cpuhp_up+0x3c/0x130
irq event stamp: 36
hardirqs last enabled at (35): [<ffffda301e85b7bc>] finish_task_switch+0xb4/0x2b0
hardirqs last disabled at (36): [<ffffda301e812fec>] cpuhp_thread_fun+0x21c/0x248
softirqs last enabled at (0): [<ffffda301e80b184>] copy_process+0x63c/0x1ac0
softirqs last disabled at (0): [<0000000000000000>] 0x0
CPU: 0 PID: 24 Comm: cpuhp/0 Not tainted 5.19.0-rc3-rt5-[...]
Hardware name: WIWYNN Mt.Jade Server [...]
Call trace:
dump_backtrace+0x114/0x120
show_stack+0x20/0x70
dump_stack_lvl+0x9c/0xd8
dump_stack+0x18/0x34
__might_resched+0x188/0x228
rt_spin_lock+0x70/0x120
sdei_cpuhp_up+0x3c/0x130
cpuhp_invoke_callback+0x250/0xf08
cpuhp_thread_fun+0x120/0x248
smpboot_thread_fn+0x280/0x320
kthread+0x130/0x140
ret_from_fork+0x10/0x20

sdei_cpuhp_up() is called in the STARTING hotplug section,
which runs with interrupts disabled. Use a CPUHP_AP_ONLINE_DYN entry
instead to execute the cpuhp cb later, with preemption enabled.

SDEI originally got its own cpuhp slot to allow interacting
with perf. It got superseded by pNMI and this early slot is not
relevant anymore. [1]

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.

Also add a check for the SDEI_1_0_FN_SDEI_PRIVATE_RESET SDEI call
which acts on the calling CPU.

[1]:
https://lore.kernel.org/all/5813b8c5-ae3e-87fd-fccc-94c9cd08816d@xxxxxxx/

Suggested-by: James Morse <james.morse@xxxxxxx>
Signed-off-by: Pierre Gondois <pierre.gondois@xxxxxxx>
Reviewed-by: James Morse <james.morse@xxxxxxx>
---

Notes:
v3:
- Remove some unnecessary WARN_ON().
- Use a dynamic cpuhp_cb entry.
v4:
- Correct typos.

drivers/firmware/arm_sdei.c | 37 ++++++++++++++++++++-----------------
include/linux/cpuhotplug.h | 1 -
2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/drivers/firmware/arm_sdei.c b/drivers/firmware/arm_sdei.c
index 1e1a51510e83..f9040bd61081 100644
--- a/drivers/firmware/arm_sdei.c
+++ b/drivers/firmware/arm_sdei.c
@@ -43,6 +43,8 @@ static asmlinkage void (*sdei_firmware_call)(unsigned long function_id,
/* entry point from firmware to arch asm code */
static unsigned long sdei_entry_point;

+static int sdei_hp_state;
+
struct sdei_event {
/* These three are protected by the sdei_list_lock */
struct list_head list;
@@ -301,8 +303,6 @@ 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 +315,7 @@ int sdei_mask_local_cpu(void)

static void _ipi_mask_cpu(void *ignored)
{
+ WARN_ON_ONCE(preemptible());
sdei_mask_local_cpu();
}

@@ -322,8 +323,6 @@ 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 +335,7 @@ int sdei_unmask_local_cpu(void)

static void _ipi_unmask_cpu(void *ignored)
{
+ WARN_ON_ONCE(preemptible());
sdei_unmask_local_cpu();
}

@@ -343,6 +343,8 @@ 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 +391,6 @@ 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);
@@ -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);
@@ -561,8 +559,6 @@ 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);
@@ -717,6 +713,8 @@ 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 +763,7 @@ static int sdei_device_freeze(struct device *dev)
int err;

/* unregister private events */
- cpuhp_remove_state(CPUHP_AP_ARM_SDEI_STARTING);
+ cpuhp_remove_state(sdei_entry_point);

err = sdei_unregister_shared();
if (err)
@@ -786,12 +784,15 @@ 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_ONLINE_DYN, "SDEI",
&sdei_cpuhp_up, &sdei_cpuhp_down);
- if (err)
+ if (err < 0) {
pr_warn("Failed to re-register CPU hotplug notifier...\n");
+ return err;
+ }

- return err;
+ sdei_hp_state = err;
+ return 0;
}

static int sdei_device_restore(struct device *dev)
@@ -823,7 +824,7 @@ 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(sdei_hp_state);

sdei_platform_reset();

@@ -1003,13 +1004,15 @@ 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_ONLINE_DYN, "SDEI",
&sdei_cpuhp_up, &sdei_cpuhp_down);
- if (err) {
+ if (err < 0) {
pr_warn("Failed to register CPU hotplug notifier...\n");
goto remove_reboot;
}

+ sdei_hp_state = err;
+
return 0;

remove_reboot:
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 6c6859bfc454..7e392e51883a 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -163,7 +163,6 @@ 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,
--
2.25.1

Next message: Pierre Gondois: "Re: [PATCH v3] firmware: arm_sdei: Fix sleep from invalid context BUG"
Previous message: Francesco Dolcini: "Re: [PATCH v3 5/5] arm64: dts: imx8mp-verdin: add 88W8997 serdev to uart4"
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