[PATCH net v2 1/2] ptp: drain virtual clock sysfs operations before unregistering children

[James Hilliard <james.hilliard1@gmail.com>]

Parent clock removal walks its virtual clocks before removing the
n_vclocks sysfs attribute. The mutex taken by ptp_vclock_in_use() is
released before that walk, so a concurrent sysfs deletion can pick the
same child and unregister and free its ptp_vclock a second time. A
reference held by the device iterator does not protect that separately
allocated virtual clock.

Remove n_vclocks before walking the children. Removing the attribute
prevents new stores and drains stores already running, without holding
n_vclocks_mux across a callback that needs that mutex. Virtual clocks
have no such attribute and must not remove the parent attribute when
being deleted by its active store.

This race was found by code inspection of virtual-clock registration
failure cleanup and parent removal.

Fixes: 5d43f951b1ac ("ptp: add ptp virtual clock driver framework")
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
 drivers/ptp/ptp_clock.c   | 5 +++++
 drivers/ptp/ptp_private.h | 1 +
 drivers/ptp/ptp_sysfs.c   | 6 ++++++
 3 files changed, 12 insertions(+)

diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
index 4111342d64f0..47ffc773065a 100644
--- a/drivers/ptp/ptp_clock.c
+++ b/drivers/ptp/ptp_clock.c
@@ -508,6 +508,11 @@ static int unregister_vclock(struct device *dev, void *data)
 
 int ptp_clock_unregister(struct ptp_clock *ptp)
 {
+	/*
+	 * Stop and drain virtual-clock creation and deletion before walking the
+	 * children. Do not hold n_vclocks_mux while waiting for sysfs callbacks.
+	 */
+	ptp_vclock_remove_sysfs(ptp);
 	if (ptp_vclock_in_use(ptp)) {
 		device_for_each_child(&ptp->dev, NULL, unregister_vclock);
 	}
diff --git a/drivers/ptp/ptp_private.h b/drivers/ptp/ptp_private.h
index db4039d642b4..ec8633126d6b 100644
--- a/drivers/ptp/ptp_private.h
+++ b/drivers/ptp/ptp_private.h
@@ -169,6 +169,7 @@ extern const struct attribute_group *ptp_groups[];
 
 int ptp_populate_pin_groups(struct ptp_clock *ptp);
 void ptp_cleanup_pin_groups(struct ptp_clock *ptp);
+void ptp_vclock_remove_sysfs(struct ptp_clock *ptp);
 
 struct ptp_vclock *ptp_vclock_register(struct ptp_clock *pclock);
 void ptp_vclock_unregister(struct ptp_vclock *vclock);
diff --git a/drivers/ptp/ptp_sysfs.c b/drivers/ptp/ptp_sysfs.c
index dc398c6b7528..53388b123198 100644
--- a/drivers/ptp/ptp_sysfs.c
+++ b/drivers/ptp/ptp_sysfs.c
@@ -263,6 +263,12 @@ static ssize_t n_vclocks_store(struct device *dev,
 }
 static DEVICE_ATTR_RW(n_vclocks);
 
+void ptp_vclock_remove_sysfs(struct ptp_clock *ptp)
+{
+	if (!ptp->is_virtual_clock)
+		device_remove_file(&ptp->dev, &dev_attr_n_vclocks);
+}
+
 static ssize_t max_vclocks_show(struct device *dev,
 				struct device_attribute *attr, char *page)
 {

-- 
2.53.0