Merge: ptp: stable backport for 9.8 phase 2

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/7386

JIRA: https://issues.redhat.com/browse/RHEL-115644

 * 87f7ce2 ptp: remove ptp->n_vclocks check logic in ptp_vclock_in_use()
 * 5ab73b0 ptp: fix breakage after ptp_vclock_in_use() rework
 * aa112cb ptp: allow reading of currently dialed frequency to succeed on free-running clocks
 * 2efe412 ptp: prevent possible ABBA deadlock in ptp_clock_freerun()

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

---

<small>Created 2025-09-23 02:42 UTC by backporter - [KWF FAQ](https://red.ht/kernel_workflow_doc) - [Slack #team-kernel-workflow](https://redhat-internal.slack.com/archives/C04LRUPMJQ5) - [Source](https://gitlab.com/cki-project/kernel-workflow/-/blob/main/webhook/utils/backporter.py) - [Documentation](https://gitlab.com/cki-project/kernel-workflow/-/blob/main/docs/README.backporter.md) - [Report an issue](https://issues.redhat.com/secure/CreateIssueDetails!init.jspa?pid=12334433&issuetype=1&priority=4&summary=backporter+webhook+issue&components=kernel-workflow+/+backporter)</small>

Approved-by: Jiri Benc <jbenc@redhat.com>
Approved-by: Hangbin Liu <haliu@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: CKI GitLab Kmaint Pipeline Bot <26919896-cki-kmaint-pipeline-bot@users.noreply.gitlab.com>

Author: CKI KWF Bot

drivers/ptp/ptp_clock.c

@@ -107,7 +107,8 @@ static int ptp_clock_adjtime(struct posix_clock *pc, struct __kernel_timex *tx)
 	struct ptp_clock_info *ops;
 	int err = -EOPNOTSUPP;
 
-	if (ptp_clock_freerun(ptp)) {
+	if (tx->modes & (ADJ_SETOFFSET | ADJ_FREQUENCY | ADJ_OFFSET) &&
+	    ptp_clock_freerun(ptp)) {
 		pr_err("ptp: physical clock is free running\n");
 		return -EBUSY;
 	}

drivers/ptp/ptp_private.h

@@ -20,6 +20,11 @@
 #define PTP_BUF_TIMESTAMPS 30
 #define PTP_DEFAULT_MAX_VCLOCKS 20
 
+enum {
+	PTP_LOCK_PHYSICAL = 0,
+	PTP_LOCK_VIRTUAL,
+};
+
 struct timestamp_event_queue {
 	struct ptp_extts_event buf[PTP_MAX_TIMESTAMPS];
 	int head;
@@ -91,10 +96,20 @@ static inline bool ptp_vclock_in_use(struct ptp_clock *ptp)
 {
 	bool in_use = false;
 
+	/* Virtual clocks can't be stacked on top of virtual clocks.
+	 * Avoid acquiring the n_vclocks_mux on virtual clocks, to allow this
+	 * function to be called from code paths where the n_vclocks_mux of the
+	 * parent physical clock is already held. Functionally that's not an
+	 * issue, but lockdep would complain, because they have the same lock
+	 * class.
+	 */
+	if (ptp->is_virtual_clock)
+		return false;
+
 	if (mutex_lock_interruptible(&ptp->n_vclocks_mux))
 		return true;
 
-	if (!ptp->is_virtual_clock && ptp->n_vclocks)
+	if (ptp->n_vclocks)
 		in_use = true;
 
 	mutex_unlock(&ptp->n_vclocks_mux);

drivers/ptp/ptp_vclock.c

@@ -154,6 +154,11 @@ static long ptp_vclock_refresh(struct ptp_clock_info *ptp)
 	return PTP_VCLOCK_REFRESH_INTERVAL;
 }
 
+static void ptp_vclock_set_subclass(struct ptp_clock *ptp)
+{
+	lockdep_set_subclass(&ptp->clock.rwsem, PTP_LOCK_VIRTUAL);
+}
+
 static const struct ptp_clock_info ptp_vclock_info = {
 	.owner		= THIS_MODULE,
 	.name		= "ptp virtual clock",
@@ -213,6 +218,8 @@ struct ptp_vclock *ptp_vclock_register(struct ptp_clock *pclock)
 		return NULL;
 	}
 
+	ptp_vclock_set_subclass(vclock->clock);
+
 	timecounter_init(&vclock->tc, &vclock->cc, 0);
 	ptp_schedule_worker(vclock->clock, PTP_VCLOCK_REFRESH_INTERVAL);