[PATCH net v3 1/5] 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. Skip virtual
clocks, which do not have this attribute.

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

Fixes: bfcbb76b0f59 ("ptp: unregister virtual clocks when unregistering physical clock.")
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