Commit b22800f9 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Jakub Kicinski
Browse files

dev: Use nested-BH locking for softnet_data.process_queue. 



softnet_data::process_queue is a per-CPU variable and relies on disabled
BH for its locking. Without per-CPU locking in local_bh_disable() on
PREEMPT_RT this data structure requires explicit locking.

softnet_data::input_queue_head can be updated lockless. This is fine
because this value is only update CPU local by the local backlog_napi
thread.

Add a local_lock_t to softnet_data and use local_lock_nested_bh() for locking
of process_queue. This change adds only lockdep coverage and does not
alter the functional behaviour for !PREEMPT_RT.

Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20240620132727.660738-11-bigeasy@linutronix.de


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent a8760d0d

include/linux/netdevice.h

+1 −0
Original line number Diff line number Diff line
@@ -3202,6 +3202,7 @@ static inline bool dev_has_header(const struct net_device *dev) 
struct softnet_data {

	struct list_head	poll_list;

	struct sk_buff_head	process_queue;

	local_lock_t		process_queue_bh_lock;



	/* stats */

	unsigned int		processed;

net/core/dev.c

+11 −1
Original line number Diff line number Diff line
@@ -449,7 +449,9 @@ static RAW_NOTIFIER_HEAD(netdev_chain); 
 *	queue in the local softnet handler.

 */



DEFINE_PER_CPU_ALIGNED(struct softnet_data, softnet_data);

DEFINE_PER_CPU_ALIGNED(struct softnet_data, softnet_data) = {

	.process_queue_bh_lock = INIT_LOCAL_LOCK(process_queue_bh_lock),

};

EXPORT_PER_CPU_SYMBOL(softnet_data);



/* Page_pool has a lockless array/stack to alloc/recycle pages.
@@ -5949,6 +5951,7 @@ static void flush_backlog(struct work_struct *work) 
	}

	backlog_unlock_irq_enable(sd);



	local_lock_nested_bh(&softnet_data.process_queue_bh_lock);

	skb_queue_walk_safe(&sd->process_queue, skb, tmp) {

		if (skb->dev->reg_state == NETREG_UNREGISTERING) {

			__skb_unlink(skb, &sd->process_queue);
@@ -5956,6 +5959,7 @@ static void flush_backlog(struct work_struct *work) 
			rps_input_queue_head_incr(sd);

		}

	}

	local_unlock_nested_bh(&softnet_data.process_queue_bh_lock);

	local_bh_enable();

}
@@ -6077,7 +6081,9 @@ static int process_backlog(struct napi_struct *napi, int quota) 
	while (again) {

		struct sk_buff *skb;



		local_lock_nested_bh(&softnet_data.process_queue_bh_lock);

		while ((skb = __skb_dequeue(&sd->process_queue))) {

			local_unlock_nested_bh(&softnet_data.process_queue_bh_lock);

			rcu_read_lock();

			__netif_receive_skb(skb);

			rcu_read_unlock();
@@ -6086,7 +6092,9 @@ static int process_backlog(struct napi_struct *napi, int quota) 
				return work;

			}



			local_lock_nested_bh(&softnet_data.process_queue_bh_lock);

		}

		local_unlock_nested_bh(&softnet_data.process_queue_bh_lock);



		backlog_lock_irq_disable(sd);

		if (skb_queue_empty(&sd->input_pkt_queue)) {
@@ -6101,8 +6109,10 @@ static int process_backlog(struct napi_struct *napi, int quota) 
			napi->state &= NAPIF_STATE_THREADED;

			again = false;

		} else {

			local_lock_nested_bh(&softnet_data.process_queue_bh_lock);

			skb_queue_splice_tail_init(&sd->input_pkt_queue,

						   &sd->process_queue);

			local_unlock_nested_bh(&softnet_data.process_queue_bh_lock);

		}

		backlog_unlock_irq_enable(sd);

	}