netdev - [PATCH v2 net-next 2/3] net: dsa: mv88e6xxx: disable hold of chip lock for handling

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Date:   Tue, 13 Dec 2022 18:46:49 +0100
From:   "Hans J. Schultz" <netdev@...io-technology.com>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     netdev@...r.kernel.org,
        "Hans J. Schultz" <netdev@...io-technology.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2 net-next 2/3] net: dsa: mv88e6xxx: disable hold of chip lock for handling

As functions called under the interrupt handler will need to take the
netlink lock, we need to release the chip lock before calling those
functions as otherwise double lock deadlocks will occur as userspace
calls towards the driver often take the netlink lock and then the
chip lock.

The deadlock would look like:

Interrupt handler: chip lock taken, but cannot take netlink lock as
                   userspace config call has netlink lock.
Userspace config: netlink lock taken, but cannot take chip lock as
                   the interrupt handler has the chip lock.

Signed-off-by: Hans J. Schultz <netdev@...io-technology.com>
---
 drivers/net/dsa/mv88e6xxx/global1_atu.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/global1_atu.c b/drivers/net/dsa/mv88e6xxx/global1_atu.c
index 61ae2d61e25c..34203e112eef 100644
--- a/drivers/net/dsa/mv88e6xxx/global1_atu.c
+++ b/drivers/net/dsa/mv88e6xxx/global1_atu.c
@@ -409,11 +409,11 @@ static irqreturn_t mv88e6xxx_g1_atu_prob_irq_thread_fn(int irq, void *dev_id)
 
 	err = mv88e6xxx_g1_read_atu_violation(chip);
 	if (err)
-		goto out;
+		goto out_unlock;
 
 	err = mv88e6xxx_g1_read(chip, MV88E6XXX_G1_ATU_OP, &val);
 	if (err)
-		goto out;
+		goto out_unlock;
 
 	err = mv88e6xxx_g1_atu_fid_read(chip, &fid);
 	if (err)
@@ -421,11 +421,13 @@ static irqreturn_t mv88e6xxx_g1_atu_prob_irq_thread_fn(int irq, void *dev_id)
 
 	err = mv88e6xxx_g1_atu_data_read(chip, &entry);
 	if (err)
-		goto out;
+		goto out_unlock;
 
 	err = mv88e6xxx_g1_atu_mac_read(chip, &entry);
 	if (err)
-		goto out;
+		goto out_unlock;
+
+	mv88e6xxx_reg_unlock(chip);
 
 	spid = entry.state;
 
@@ -449,13 +451,13 @@ static irqreturn_t mv88e6xxx_g1_atu_prob_irq_thread_fn(int irq, void *dev_id)
 						   fid);
 		chip->ports[spid].atu_full_violation++;
 	}
-	mv88e6xxx_reg_unlock(chip);
 
 	return IRQ_HANDLED;
 
-out:
+out_unlock:
 	mv88e6xxx_reg_unlock(chip);
 
+out:
 	dev_err(chip->dev, "ATU problem: error %d while handling interrupt\n",
 		err);
 	return IRQ_HANDLED;
-- 
2.34.1