ptp: vclock: use mutex to fix "sleep on atomic" bug

vclocks were using spinlocks to protect access to its timecounter and
cyclecounter. Access to timecounter/cyclecounter is backed by the same
driver callbacks that are used for non-virtual PHCs, but the usage of
the spinlock imposes a new limitation that didn't exist previously: now
they're called in atomic context so they mustn't sleep.

Some drivers like sfc or ice may sleep on these callbacks, causing
errors like "BUG: scheduling while atomic: ptp5/25223/0x00000002"

Fix it replacing the vclock's spinlock by a mutex. It fix the mentioned
bug and it doesn't introduce longer delays.

I've tested synchronizing various different combinations of clocks:
- vclock->sysclock
- sysclock->vclock
- vclock->vclock
- hardware PHC in different NIC -> vclock
- created 4 vclocks and launch 4 parallel phc2sys processes with
  lockdep enabled

In all cases, comparing the delays reported by phc2sys, they are in the
same range of values than before applying the patch.

Link: https://lore.kernel.org/netdev/69d0ff33-bd32-6aa5-d36c-fbdc3c01337c@redhat.com/
Fixes: 5d43f95 ("ptp: add ptp virtual clock driver framework")
Reported-by: Yalin Li <yalli@redhat.com>
Suggested-by: Richard Cochran <richardcochran@gmail.com>
Tested-by: Miroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: Íñigo Huguet <ihuguet@redhat.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Link: https://lore.kernel.org/r/20230221130616.21837-1-ihuguet@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/ptp/ptp_private.h

@@ -66,7 +66,7 @@ struct ptp_vclock {
 	struct hlist_node vclock_hash_node;
 	struct cyclecounter cc;
 	struct timecounter tc;
-	spinlock_t lock;	/* protects tc/cc */
+	struct mutex lock;	/* protects tc/cc */
 };
 
 /*

drivers/ptp/ptp_vclock.c

@@ -43,28 +43,28 @@ static void ptp_vclock_hash_del(struct ptp_vclock *vclock)
 static int ptp_vclock_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
 {
 	struct ptp_vclock *vclock = info_to_vclock(ptp);
-	unsigned long flags;
 	s64 adj;
 
 	adj = (s64)scaled_ppm << PTP_VCLOCK_FADJ_SHIFT;
 	adj = div_s64(adj, PTP_VCLOCK_FADJ_DENOMINATOR);
 
-	spin_lock_irqsave(&vclock->lock, flags);
+	if (mutex_lock_interruptible(&vclock->lock))
+		return -EINTR;
 	timecounter_read(&vclock->tc);
 	vclock->cc.mult = PTP_VCLOCK_CC_MULT + adj;
-	spin_unlock_irqrestore(&vclock->lock, flags);
+	mutex_unlock(&vclock->lock);
 
 	return 0;
 }
 
 static int ptp_vclock_adjtime(struct ptp_clock_info *ptp, s64 delta)
 {
 	struct ptp_vclock *vclock = info_to_vclock(ptp);
-	unsigned long flags;
 
-	spin_lock_irqsave(&vclock->lock, flags);
+	if (mutex_lock_interruptible(&vclock->lock))
+		return -EINTR;
 	timecounter_adjtime(&vclock->tc, delta);
-	spin_unlock_irqrestore(&vclock->lock, flags);
+	mutex_unlock(&vclock->lock);
 
 	return 0;
 }
@@ -73,12 +73,12 @@ static int ptp_vclock_gettime(struct ptp_clock_info *ptp,
 			      struct timespec64 *ts)
 {
 	struct ptp_vclock *vclock = info_to_vclock(ptp);
-	unsigned long flags;
 	u64 ns;
 
-	spin_lock_irqsave(&vclock->lock, flags);
+	if (mutex_lock_interruptible(&vclock->lock))
+		return -EINTR;
 	ns = timecounter_read(&vclock->tc);
-	spin_unlock_irqrestore(&vclock->lock, flags);
+	mutex_unlock(&vclock->lock);
 	*ts = ns_to_timespec64(ns);
 
 	return 0;
@@ -91,17 +91,17 @@ static int ptp_vclock_gettimex(struct ptp_clock_info *ptp,
 	struct ptp_vclock *vclock = info_to_vclock(ptp);
 	struct ptp_clock *pptp = vclock->pclock;
 	struct timespec64 pts;
-	unsigned long flags;
 	int err;
 	u64 ns;
 
 	err = pptp->info->getcyclesx64(pptp->info, &pts, sts);
 	if (err)
 		return err;
 
-	spin_lock_irqsave(&vclock->lock, flags);
+	if (mutex_lock_interruptible(&vclock->lock))
+		return -EINTR;
 	ns = timecounter_cyc2time(&vclock->tc, timespec64_to_ns(&pts));
-	spin_unlock_irqrestore(&vclock->lock, flags);
+	mutex_unlock(&vclock->lock);
 
 	*ts = ns_to_timespec64(ns);
 
@@ -113,11 +113,11 @@ static int ptp_vclock_settime(struct ptp_clock_info *ptp,
 {
 	struct ptp_vclock *vclock = info_to_vclock(ptp);
 	u64 ns = timespec64_to_ns(ts);
-	unsigned long flags;
 
-	spin_lock_irqsave(&vclock->lock, flags);
+	if (mutex_lock_interruptible(&vclock->lock))
+		return -EINTR;
 	timecounter_init(&vclock->tc, &vclock->cc, ns);
-	spin_unlock_irqrestore(&vclock->lock, flags);
+	mutex_unlock(&vclock->lock);
 
 	return 0;
 }
@@ -127,17 +127,17 @@ static int ptp_vclock_getcrosststamp(struct ptp_clock_info *ptp,
 {
 	struct ptp_vclock *vclock = info_to_vclock(ptp);
 	struct ptp_clock *pptp = vclock->pclock;
-	unsigned long flags;
 	int err;
 	u64 ns;
 
 	err = pptp->info->getcrosscycles(pptp->info, xtstamp);
 	if (err)
 		return err;
 
-	spin_lock_irqsave(&vclock->lock, flags);
+	if (mutex_lock_interruptible(&vclock->lock))
+		return -EINTR;
 	ns = timecounter_cyc2time(&vclock->tc, ktime_to_ns(xtstamp->device));
-	spin_unlock_irqrestore(&vclock->lock, flags);
+	mutex_unlock(&vclock->lock);
 
 	xtstamp->device = ns_to_ktime(ns);
 
@@ -205,7 +205,7 @@ struct ptp_vclock *ptp_vclock_register(struct ptp_clock *pclock)
 
 	INIT_HLIST_NODE(&vclock->vclock_hash_node);
 
-	spin_lock_init(&vclock->lock);
+	mutex_init(&vclock->lock);
 
 	vclock->clock = ptp_clock_register(&vclock->info, &pclock->dev);
 	if (IS_ERR_OR_NULL(vclock->clock)) {
@@ -269,7 +269,6 @@ ktime_t ptp_convert_timestamp(const ktime_t *hwtstamp, int vclock_index)
 {
 	unsigned int hash = vclock_index % HASH_SIZE(vclock_hash);
 	struct ptp_vclock *vclock;
-	unsigned long flags;
 	u64 ns;
 	u64 vclock_ns = 0;
 
@@ -281,9 +280,10 @@ ktime_t ptp_convert_timestamp(const ktime_t *hwtstamp, int vclock_index)
 		if (vclock->clock->index != vclock_index)
 			continue;
 
-		spin_lock_irqsave(&vclock->lock, flags);
+		if (mutex_lock_interruptible(&vclock->lock))
+			break;
 		vclock_ns = timecounter_cyc2time(&vclock->tc, ns);
-		spin_unlock_irqrestore(&vclock->lock, flags);
+		mutex_unlock(&vclock->lock);
 		break;
 	}