linux-kernel - [RFC PATCH PREEMPT_RT 4.19 STABLE] net: Fix compiler warnings on 4.19 PREEMPT_RT with xmit_lock

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Message-Id: <20220131162838.1C48CC340ED@smtp.kernel.org>
Date:   Thu, 13 Jan 2022 17:12:15 -0600
From:   Clark Williams <williams@...hat.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH PREEMPT_RT 4.19 STABLE] net: Fix compiler warnings on 4.19 PREEMPT_RT with xmit_lock_owner

GCC 11 has started complaining about the PREEMPT_RT changes to 2fd949365fe6628fb2
which change the xmit_lock_owner from an integer to a pointer to struct
task_struct. These changes are from the patch:

	     net: move xmit_recursion to per-task variable on -RT

The below patch is ugly but fixes the compiler warnings.

I'd be happy to entertain a better/cleaner solution

Signed-off-by: Clark Williams <williams@...hat.com>
---
 include/linux/netdevice.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 7b34ce34114a..fa2a52d24218 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3921,7 +3921,11 @@ static inline void __netif_tx_lock(struct netdev_queue *txq, int cpu)
 {
 	spin_lock(&txq->_xmit_lock);
 	/* Pairs with READ_ONCE() in __dev_queue_xmit() */
+#ifdef CONFIG_PREEMPT_RT_FULL
+	WRITE_ONCE(txq->xmit_lock_owner, current);
+#else
 	WRITE_ONCE(txq->xmit_lock_owner, cpu);
+#endif
 }
 
 static inline bool __netif_tx_acquire(struct netdev_queue *txq)
@@ -3939,7 +3943,11 @@ static inline void __netif_tx_lock_bh(struct netdev_queue *txq)
 {
 	spin_lock_bh(&txq->_xmit_lock);
 	/* Pairs with READ_ONCE() in __dev_queue_xmit() */
+#ifdef CONFIG_PREEMPT_RT_FULL
+	WRITE_ONCE(txq->xmit_lock_owner, current);
+#else
 	WRITE_ONCE(txq->xmit_lock_owner, smp_processor_id());
+#endif
 }
 
 static inline bool __netif_tx_trylock(struct netdev_queue *txq)
@@ -3948,7 +3956,11 @@ static inline bool __netif_tx_trylock(struct netdev_queue *txq)
 
 	if (likely(ok)) {
 		/* Pairs with READ_ONCE() in __dev_queue_xmit() */
+#ifdef CONFIG_PREEMPT_RT_FULL
+		WRITE_ONCE(txq->xmit_lock_owner, current);
+#else
 		WRITE_ONCE(txq->xmit_lock_owner, smp_processor_id());
+#endif
 	}
 	return ok;
 }
@@ -3956,14 +3968,22 @@ static inline bool __netif_tx_trylock(struct netdev_queue *txq)
 static inline void __netif_tx_unlock(struct netdev_queue *txq)
 {
 	/* Pairs with READ_ONCE() in __dev_queue_xmit() */
+#ifdef CONFIG_PREEMPT_RT_FULL
+	WRITE_ONCE(txq->xmit_lock_owner, NULL);
+#else
 	WRITE_ONCE(txq->xmit_lock_owner, -1);
+#endif
 	spin_unlock(&txq->_xmit_lock);
 }
 
 static inline void __netif_tx_unlock_bh(struct netdev_queue *txq)
 {
 	/* Pairs with READ_ONCE() in __dev_queue_xmit() */
+#ifdef CONFIG_PREEMPT_RT_FULL
+	WRITE_ONCE(txq->xmit_lock_owner, NULL);
+#else
 	WRITE_ONCE(txq->xmit_lock_owner, -1);
+#endif
 	spin_unlock_bh(&txq->_xmit_lock);
 }
 
-- 
2.34.1