[PATCH net-next 09/24] dev: Use the RPS lock for softnet_data::input_pkt_queue on PREEMPT_RT.
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: 2023-12-15 17:10:37
Also in:
lkml
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
There is no additional locking in rps_lock_*() on PREEMPT_RT in the !CONFIG_RPS case. The reasoning is that local_bh_disable() provides the required synchronization (everywhere). All interrupts are threaded and so the required CPU local synchronization is provided by the per-CPU lock in local_bh_disable() which is always performed for the forced-threaded interrupts. Needless to say that the softirq users (NAPI) have BH disabled while being invoked as a softirq callback. Without locking in local_bh_disable() on PREEMPT_RT the softnet_data::input_pkt_queue data structure requires explicit locking in the !CONFIG_RPS case. Disabling interrupts for CPU-local locking is undesired because it will impose restrictions within the locked sections like not allowing to free a skb. Utilise the locking which is present in the CONFIG_RPS case for serialisation on PREEMPT_RT even without CONFIG_RPS enabled. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- net/core/dev.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c
index c879246be48d8..09232080843ee 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c@@ -220,34 +220,34 @@ static inline struct hlist_head *dev_index_hash(struct net *net, int ifindex) static inline void rps_lock_irqsave(struct softnet_data *sd, unsigned long *flags) { - if (IS_ENABLED(CONFIG_RPS)) + if (IS_ENABLED(CONFIG_RPS) || IS_ENABLED(CONFIG_PREEMPT_RT)) spin_lock_irqsave(&sd->input_pkt_queue.lock, *flags); - else if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + else local_irq_save(*flags); } static inline void rps_lock_irq_disable(struct softnet_data *sd) { - if (IS_ENABLED(CONFIG_RPS)) + if (IS_ENABLED(CONFIG_RPS) || IS_ENABLED(CONFIG_PREEMPT_RT)) spin_lock_irq(&sd->input_pkt_queue.lock); - else if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + else local_irq_disable(); } static inline void rps_unlock_irq_restore(struct softnet_data *sd, unsigned long *flags) { - if (IS_ENABLED(CONFIG_RPS)) + if (IS_ENABLED(CONFIG_RPS) || IS_ENABLED(CONFIG_PREEMPT_RT)) spin_unlock_irqrestore(&sd->input_pkt_queue.lock, *flags); - else if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + else local_irq_restore(*flags); } static inline void rps_unlock_irq_enable(struct softnet_data *sd) { - if (IS_ENABLED(CONFIG_RPS)) + if (IS_ENABLED(CONFIG_RPS) || IS_ENABLED(CONFIG_PREEMPT_RT)) spin_unlock_irq(&sd->input_pkt_queue.lock); - else if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + else local_irq_enable(); }
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2.43.0