netdev - [PATCH net-next 2/2] net: sfp: add mutex to prevent concurrent state checks

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Date:   Fri,  7 Jun 2019 10:42:36 -0600
From:   Robert Hancock <hancock@...systems.ca>
To:     netdev@...r.kernel.org
Cc:     linux@...linux.org.uk, andrew@...n.ch, f.fainelli@...il.com,
        hkallweit1@...il.com, Robert Hancock <hancock@...systems.ca>
Subject: [PATCH net-next 2/2] net: sfp: add mutex to prevent concurrent state checks

sfp_check_state can potentially be called by both a threaded IRQ handler
and delayed work. If it is concurrently called, it could result in
incorrect state management. Add a st_mutex to protect the state - this
lock gets taken outside of code that checks and handle state changes, and
the existing sm_mutex nests inside of it.

Suggested-by: Russell King <rmk+kernel@...linux.org.uk>
Signed-off-by: Robert Hancock <hancock@...systems.ca>
---
 drivers/net/phy/sfp.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c
index 01af080..edd2de5 100644
--- a/drivers/net/phy/sfp.c
+++ b/drivers/net/phy/sfp.c
@@ -188,10 +188,11 @@ struct sfp {
 	int gpio_irq[GPIO_MAX];
 
 	bool attached;
+	struct mutex st_mutex;			/* Protects state */
 	unsigned int state;
 	struct delayed_work poll;
 	struct delayed_work timeout;
-	struct mutex sm_mutex;
+	struct mutex sm_mutex;			/* Protects state machine */
 	unsigned char sm_mod_state;
 	unsigned char sm_dev_state;
 	unsigned short sm_state;
@@ -1705,6 +1706,7 @@ static void sfp_check_state(struct sfp *sfp)
 {
 	unsigned int state, i, changed;
 
+	mutex_lock(&sfp->st_mutex);
 	state = sfp_get_state(sfp);
 	changed = state ^ sfp->state;
 	changed &= SFP_F_PRESENT | SFP_F_LOS | SFP_F_TX_FAULT;
@@ -1730,6 +1732,7 @@ static void sfp_check_state(struct sfp *sfp)
 		sfp_sm_event(sfp, state & SFP_F_LOS ?
 				SFP_E_LOS_HIGH : SFP_E_LOS_LOW);
 	rtnl_unlock();
+	mutex_unlock(&sfp->st_mutex);
 }
 
 static irqreturn_t sfp_irq(int irq, void *data)
@@ -1760,6 +1763,7 @@ static struct sfp *sfp_alloc(struct device *dev)
 	sfp->dev = dev;
 
 	mutex_init(&sfp->sm_mutex);
+	mutex_init(&sfp->st_mutex);
 	INIT_DELAYED_WORK(&sfp->poll, sfp_poll);
 	INIT_DELAYED_WORK(&sfp->timeout, sfp_timeout);
 
-- 
1.8.3.1