[PATCH v4 3/3] pps: convert pps_kc_hardpps_lock to raw_spinlock for PREEMPT_RT

[Michael Byczkowski]

Convert pps_kc_hardpps_lock from spinlock_t to raw_spinlock_t. This
lock is held in pps_kc_event() which calls hardpps(). hardpps() takes
tk_core.lock which is already a raw_spinlock — nesting a sleeping lock
(PREEMPT_RT spinlock_t) over a raw_spinlock is invalid.

The locked section only checks a pointer comparison and calls
hardpps(), both of which are non-sleeping.

On non-RT kernels, raw_spinlock_t compiles to identical code as
spinlock_t — no behavioral change.

Signed-off-by: Michael Byczkowski <by@xxxxxxxxxxxx>
Acked-by: Rodolfo Giometti <giometti@xxxxxxxxxxxx>
Tested-by: Michael Byczkowski <by@xxxxxxxxxxxx>
Tested-by: Calvin Owens <calvin@xxxxxxxxxx>
---
 drivers/pps/kc.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/pps/kc.c b/drivers/pps/kc.c
index fbd23295afd7..9c6c024d5083 100644
--- a/drivers/pps/kc.c
+++ b/drivers/pps/kc.c
@@ -21,7 +21,7 @@
  */
 
 /* state variables to bind kernel consumer */
-static DEFINE_SPINLOCK(pps_kc_hardpps_lock);
+static DEFINE_RAW_SPINLOCK(pps_kc_hardpps_lock);
 /* PPS API (RFC 2783): current source and mode for kernel consumer */
 static struct pps_device *pps_kc_hardpps_dev;	/* unique pointer to device */
 static int pps_kc_hardpps_mode;		/* mode bits for kernel consumer */
@@ -36,17 +36,17 @@ static int pps_kc_hardpps_mode;		/* mode bits for kernel consumer */
 int pps_kc_bind(struct pps_device *pps, struct pps_bind_args *bind_args)
 {
 	/* Check if another consumer is already bound */
-	spin_lock_irq(&pps_kc_hardpps_lock);
+	raw_spin_lock_irq(&pps_kc_hardpps_lock);
 
 	if (bind_args->edge == 0)
 		if (pps_kc_hardpps_dev == pps) {
 			pps_kc_hardpps_mode = 0;
 			pps_kc_hardpps_dev = NULL;
-			spin_unlock_irq(&pps_kc_hardpps_lock);
+			raw_spin_unlock_irq(&pps_kc_hardpps_lock);
 			dev_info(&pps->dev, "unbound kernel"
 					" consumer\n");
 		} else {
-			spin_unlock_irq(&pps_kc_hardpps_lock);
+			raw_spin_unlock_irq(&pps_kc_hardpps_lock);
 			dev_err(&pps->dev, "selected kernel consumer"
 					" is not bound\n");
 			return -EINVAL;
@@ -56,11 +56,11 @@ int pps_kc_bind(struct pps_device *pps, struct pps_bind_args *bind_args)
 				pps_kc_hardpps_dev == pps) {
 			pps_kc_hardpps_mode = bind_args->edge;
 			pps_kc_hardpps_dev = pps;
-			spin_unlock_irq(&pps_kc_hardpps_lock);
+			raw_spin_unlock_irq(&pps_kc_hardpps_lock);
 			dev_info(&pps->dev, "bound kernel consumer: "
 				"edge=0x%x\n", bind_args->edge);
 		} else {
-			spin_unlock_irq(&pps_kc_hardpps_lock);
+			raw_spin_unlock_irq(&pps_kc_hardpps_lock);
 			dev_err(&pps->dev, "another kernel consumer"
 					" is already bound\n");
 			return -EINVAL;
@@ -78,15 +78,15 @@ int pps_kc_bind(struct pps_device *pps, struct pps_bind_args *bind_args)
  */
 void pps_kc_remove(struct pps_device *pps)
 {
-	spin_lock_irq(&pps_kc_hardpps_lock);
+	raw_spin_lock_irq(&pps_kc_hardpps_lock);
 	if (pps == pps_kc_hardpps_dev) {
 		pps_kc_hardpps_mode = 0;
 		pps_kc_hardpps_dev = NULL;
-		spin_unlock_irq(&pps_kc_hardpps_lock);
+		raw_spin_unlock_irq(&pps_kc_hardpps_lock);
 		dev_info(&pps->dev, "unbound kernel consumer"
 				" on device removal\n");
 	} else
-		spin_unlock_irq(&pps_kc_hardpps_lock);
+		raw_spin_unlock_irq(&pps_kc_hardpps_lock);
 }
 
 /* pps_kc_event - call hardpps() on PPS event
@@ -102,8 +102,8 @@ void pps_kc_event(struct pps_device *pps, struct pps_event_time *ts,
 	unsigned long flags;
 
 	/* Pass some events to kernel consumer if activated */
-	spin_lock_irqsave(&pps_kc_hardpps_lock, flags);
+	raw_spin_lock_irqsave(&pps_kc_hardpps_lock, flags);
 	if (pps == pps_kc_hardpps_dev && event & pps_kc_hardpps_mode)
 		hardpps(&ts->ts_real, &ts->ts_raw);
-	spin_unlock_irqrestore(&pps_kc_hardpps_lock, flags);
+	raw_spin_unlock_irqrestore(&pps_kc_hardpps_lock, flags);
 }
-- 
2.47.3