ptp: Avoid deadlocks in the programmable pin code.

The PTP Hardware Clock (PHC) subsystem offers an API for configuring
programmable pins.  User space sets or gets the settings using ioctls,
and drivers verify dialed settings via a callback.  Drivers may also
query pin settings by calling the ptp_find_pin() method.

Although the core subsystem protects concurrent access to the pin
settings, the implementation places illogical restrictions on how
drivers may call ptp_find_pin().  When enabling an auxiliary function
via the .enable(on=1) callback, drivers may invoke the pin finding
method, but when disabling with .enable(on=0) drivers are not
permitted to do so.  With the exception of the mv88e6xxx, all of the
PHC drivers do respect this restriction, but still the locking pattern
is both confusing and unnecessary.

This patch changes the locking implementation to allow PHC drivers to
freely call ptp_find_pin() from their .enable() and .verify()
callbacks.

V2 ChangeLog:
- fixed spelling in the kernel doc
- add Vladimir's tested by tag

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Reported-by: Yangbo Lu <yangbo.lu@nxp.com>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 24 insertions, 2 deletions

diff --git a/drivers/ptp/ptp_chardev.c b/drivers/ptp/ptp_chardev.c
index 9d72ab593f13..93d574faf1fe 100644
--- a/drivers/ptp/ptp_chardev.c
+++ b/drivers/ptp/ptp_chardev.c
@@ -175,7 +175,10 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 		}
 		req.type = PTP_CLK_REQ_EXTTS;
 		enable = req.extts.flags & PTP_ENABLE_FEATURE ? 1 : 0;
+		if (mutex_lock_interruptible(&ptp->pincfg_mux))
+			return -ERESTARTSYS;
 		err = ops->enable(ops, &req, enable);
+		mutex_unlock(&ptp->pincfg_mux);
 		break;
 
 	case PTP_PEROUT_REQUEST:
@@ -206,7 +209,10 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 		}
 		req.type = PTP_CLK_REQ_PEROUT;
 		enable = req.perout.period.sec || req.perout.period.nsec;
+		if (mutex_lock_interruptible(&ptp->pincfg_mux))
+			return -ERESTARTSYS;
 		err = ops->enable(ops, &req, enable);
+		mutex_unlock(&ptp->pincfg_mux);
 		break;
 
 	case PTP_ENABLE_PPS:
@@ -217,7 +223,10 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 			return -EPERM;
 		req.type = PTP_CLK_REQ_PPS;
 		enable = arg ? 1 : 0;
+		if (mutex_lock_interruptible(&ptp->pincfg_mux))
+			return -ERESTARTSYS;
 		err = ops->enable(ops, &req, enable);
+		mutex_unlock(&ptp->pincfg_mux);
 		break;
 
 	case PTP_SYS_OFFSET_PRECISE:
diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
index ac1f2bf9e888..acabbe72e55e 100644
--- a/drivers/ptp/ptp_clock.c
+++ b/drivers/ptp/ptp_clock.c
@@ -348,7 +348,6 @@ int ptp_find_pin(struct ptp_clock *ptp,
 	struct ptp_pin_desc *pin = NULL;
 	int i;
 
-	mutex_lock(&ptp->pincfg_mux);
 	for (i = 0; i < ptp->info->n_pins; i++) {
 		if (ptp->info->pin_config[i].func == func &&
 		    ptp->info->pin_config[i].chan == chan) {
@@ -356,12 +355,26 @@ int ptp_find_pin(struct ptp_clock *ptp,
 			break;
 		}
 	}
-	mutex_unlock(&ptp->pincfg_mux);
 
 	return pin ? i : -1;
 }
 EXPORT_SYMBOL(ptp_find_pin);
 
+int ptp_find_pin_unlocked(struct ptp_clock *ptp,
+			  enum ptp_pin_function func, unsigned int chan)
+{
+	int result;
+
+	mutex_lock(&ptp->pincfg_mux);
+
+	result = ptp_find_pin(ptp, func, chan);
+
+	mutex_unlock(&ptp->pincfg_mux);
+
+	return result;
+}
+EXPORT_SYMBOL(ptp_find_pin_unlocked);
+
 int ptp_schedule_worker(struct ptp_clock *ptp, unsigned long delay)
 {
 	return kthread_mod_delayed_work(ptp->kworker, &ptp->aux_work, delay);