[PATCH RFC] base: power: replace generic_pm_domain spinlock by raw spinlock

[Adrien Thierry <athierry@redhat.com>]

We've been encountering a BUG: scheduling while atomic while running the
5.18.0-rt11 kernel on a Qualcomm SoC (see stacktrace below).

It seems to occur because a spinlock is taken in the PSCI idle code path
in the idle loop. With the RT patchset applied and CONFIG_PREEMPT_RT
enabled, spinlocks can sleep, thus triggering the bug.

In order to prevent this, replace the generic_pm_domain spinlock by a
raw spinlock.

[    2.994433] BUG: scheduling while atomic: swapper/6/0/0x00000002
[    2.994439] Modules linked in:
[    2.994447] [<ffff80000810b0ec>] migrate_enable+0x3c/0x160
[    2.994461] CPU: 6 PID: 0 Comm: swapper/6 Not tainted 5.18.0-rt11+ #1
[    2.994464] Hardware name: Qualcomm SA8295P ADP (DT)
[    2.994466] Call trace:
[    2.994467]  dump_backtrace+0xb0/0x120
[    2.994473]  show_stack+0x1c/0x6c
[    2.994477]  dump_stack_lvl+0x64/0x7c
[    2.994483]  dump_stack+0x14/0x2c
[    2.994487]  __schedule_bug+0xa8/0xc0
[    2.994489]  schedule_debug.constprop.0+0x154/0x170
[    2.994492]  __schedule+0x58/0x520
[    2.994496]  schedule_rtlock+0x20/0x44
[    2.994499]  rtlock_slowlock_locked+0x110/0x260
[    2.994503]  rt_spin_lock+0x74/0x94
[    2.994505]  genpd_lock_nested_spin+0x20/0x30
[    2.994509]  genpd_power_off.part.0.isra.0+0x248/0x2cc
[    2.994512]  genpd_runtime_suspend+0x1a0/0x300
[    2.994515]  __rpm_callback+0x4c/0x16c
[    2.994518]  rpm_callback+0x6c/0x80
[    2.994520]  rpm_suspend+0x10c/0x63c
[    2.994523]  __pm_runtime_suspend+0x54/0xa4
[    2.994526]  __psci_enter_domain_idle_state.constprop.0+0x64/0x10c
[    2.994532]  psci_enter_domain_idle_state+0x1c/0x24
[    2.994534]  cpuidle_enter_state+0x8c/0x3f0
[    2.994539]  cpuidle_enter+0x3c/0x50
[    2.994543]  cpuidle_idle_call+0x158/0x1d4
[    2.994548]  do_idle+0xa8/0xfc
[    2.994551]  cpu_startup_entry+0x28/0x30
[    2.994556]  secondary_start_kernel+0xe4/0x140
[    2.994563]  __secondary_switched+0x54/0x58

Signed-off-by: Adrien Thierry <athierry@redhat.com>
---

This patch fixes the bug but I'm not sure if this is the proper way to do
so. Suggestions for other ways to fix this are very welcome. 

 drivers/base/power/domain.c | 10 +++++-----
 include/linux/pm_domain.h   |  2 +-
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index 739e52cd4aba..9378decb58cf 100644
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -82,7 +82,7 @@ static void genpd_lock_spin(struct generic_pm_domain *genpd)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&genpd->slock, flags);
+	raw_spin_lock_irqsave(&genpd->slock, flags);
 	genpd->lock_flags = flags;
 }
 
@@ -92,7 +92,7 @@ static void genpd_lock_nested_spin(struct generic_pm_domain *genpd,
 {
 	unsigned long flags;
 
-	spin_lock_irqsave_nested(&genpd->slock, flags, depth);
+	raw_spin_lock_irqsave_nested(&genpd->slock, flags, depth);
 	genpd->lock_flags = flags;
 }
 
@@ -101,7 +101,7 @@ static int genpd_lock_interruptible_spin(struct generic_pm_domain *genpd)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&genpd->slock, flags);
+	raw_spin_lock_irqsave(&genpd->slock, flags);
 	genpd->lock_flags = flags;
 	return 0;
 }
@@ -109,7 +109,7 @@ static int genpd_lock_interruptible_spin(struct generic_pm_domain *genpd)
 static void genpd_unlock_spin(struct generic_pm_domain *genpd)
 	__releases(&genpd->slock)
 {
-	spin_unlock_irqrestore(&genpd->slock, genpd->lock_flags);
+	raw_spin_unlock_irqrestore(&genpd->slock, genpd->lock_flags);
 }
 
 static const struct genpd_lock_ops genpd_spin_ops = {
@@ -2022,7 +2022,7 @@ static void genpd_free_data(struct generic_pm_domain *genpd)
 static void genpd_lock_init(struct generic_pm_domain *genpd)
 {
 	if (genpd->flags & GENPD_FLAG_IRQ_SAFE) {
-		spin_lock_init(&genpd->slock);
+		raw_spin_lock_init(&genpd->slock);
 		genpd->lock_ops = &genpd_spin_ops;
 	} else {
 		mutex_init(&genpd->mlock);
diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index ebc351698090..80166a915b0d 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -159,7 +159,7 @@ struct generic_pm_domain {
 	union {
 		struct mutex mlock;
 		struct {
-			spinlock_t slock;
+			raw_spinlock_t slock;
 			unsigned long lock_flags;
 		};
 	};

base-commit: 979086f5e0066b4eff66e1eee123da228489985c
-- 
2.35.3