Commit 67d93ffc authored by Íñigo Huguet's avatar Íñigo Huguet Committed by Jakub Kicinski
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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: 5d43f951 ("ptp: add ptp virtual clock driver framework")
Reported-by: default avatarYalin Li <yalli@redhat.com>
Suggested-by: default avatarRichard Cochran <richardcochran@gmail.com>
Tested-by: default avatarMiroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: default avatarÍñigo Huguet <ihuguet@redhat.com>
Acked-by: default avatarRichard Cochran <richardcochran@gmail.com>
Link: https://lore.kernel.org/r/20230221130616.21837-1-ihuguet@redhat.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 5b7c4cab

drivers/ptp/ptp_private.h

+1 −1
Original line number Diff line number Diff line
@@ -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

+22 −22
Original line number Diff line number Diff line
@@ -43,16 +43,16 @@ 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;

}
@@ -60,11 +60,11 @@ static int ptp_vclock_adjfine(struct ptp_clock_info *ptp, long scaled_ppm) 
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;
@@ -91,7 +91,6 @@ 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;
@@ -99,9 +98,10 @@ static int ptp_vclock_gettimex(struct ptp_clock_info *ptp, 
	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;

}
@@ -127,7 +127,6 @@ 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;
@@ -135,9 +134,10 @@ static int ptp_vclock_getcrosststamp(struct ptp_clock_info *ptp, 
	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;

	}