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

[ Upstream commit 67d93ffc0f3c47094750bde6d62e7c5765dc47a6 ]

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: 5d43f951b1ac ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/ptp/ptp_private.h b/drivers/ptp/ptp_private.h
index 77918a2..75f58fc 100644 (file)
--- a/drivers/ptp/ptp_private.h
+++ b/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 */
 };
 
 /*

diff --git a/drivers/ptp/ptp_vclock.c b/drivers/ptp/ptp_vclock.c
index 1c0ed48..dcf752c 100644 (file)
--- a/drivers/ptp/ptp_vclock.c
+++ b/drivers/ptp/ptp_vclock.c
@@ -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;
        }