From 26f29b14916964043bc25b55ad1b9f5e9a12ca53 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 13 Feb 2026 12:04:27 +0000 Subject: [PATCH] net: fix backlog_unlock_irq_restore() vs CONFIG_PREEMPT_RT CONFIG_PREEMPT_RT is special, make this clear in backlog_lock_irq_save() and backlog_unlock_irq_restore(). The issue shows up with CONFIG_DEBUG_IRQFLAGS=y raw_local_irq_restore() called with IRQs enabled WARNING: kernel/locking/irqflag-debug.c:10 at warn_bogus_irq_restore+0xc/0x20 kernel/locking/irqflag-debug.c:10, CPU#1: aoe_tx0/1321 Modules linked in: CPU: 1 UID: 0 PID: 1321 Comm: aoe_tx0 Not tainted syzkaller #0 PREEMPT_{RT,(full)} Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026 RIP: 0010:warn_bogus_irq_restore+0xc/0x20 kernel/locking/irqflag-debug.c:10 Call Trace: backlog_unlock_irq_restore net/core/dev.c:253 [inline] enqueue_to_backlog+0x525/0xcf0 net/core/dev.c:5347 netif_rx_internal+0x120/0x550 net/core/dev.c:5659 __netif_rx+0xa9/0x110 net/core/dev.c:5679 loopback_xmit+0x43a/0x660 drivers/net/loopback.c:90 __netdev_start_xmit include/linux/netdevice.h:5275 [inline] netdev_start_xmit include/linux/netdevice.h:5284 [inline] xmit_one net/core/dev.c:3864 [inline] dev_hard_start_xmit+0x2df/0x830 net/core/dev.c:3880 __dev_queue_xmit+0x16f4/0x3990 net/core/dev.c:4829 dev_queue_xmit include/linux/netdevice.h:3384 [inline] Fixes: 27a01c1969a5 ("net: fully inline backlog_unlock_irq_restore()") Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260213120427.2914544-1-edumazet@google.com Signed-off-by: Paolo Abeni --- net/core/dev.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/net/core/dev.c b/net/core/dev.c index ac6bcb2a0784..96f89eb797e8 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -231,10 +231,13 @@ static bool use_backlog_threads(void) static inline void backlog_lock_irq_save(struct softnet_data *sd, unsigned long *flags) { - if (IS_ENABLED(CONFIG_RPS) || use_backlog_threads()) + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { spin_lock_irqsave(&sd->input_pkt_queue.lock, *flags); - else + } else { local_irq_save(*flags); + if (IS_ENABLED(CONFIG_RPS) || use_backlog_threads()) + spin_lock(&sd->input_pkt_queue.lock); + } } static inline void backlog_lock_irq_disable(struct softnet_data *sd) @@ -248,9 +251,13 @@ static inline void backlog_lock_irq_disable(struct softnet_data *sd) static inline void backlog_unlock_irq_restore(struct softnet_data *sd, unsigned long flags) { - if (IS_ENABLED(CONFIG_RPS) || use_backlog_threads()) - spin_unlock(&sd->input_pkt_queue.lock); - local_irq_restore(flags); + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { + spin_unlock_irqrestore(&sd->input_pkt_queue.lock, flags); + } else { + if (IS_ENABLED(CONFIG_RPS) || use_backlog_threads()) + spin_unlock(&sd->input_pkt_queue.lock); + local_irq_restore(flags); + } } static inline void backlog_unlock_irq_enable(struct softnet_data *sd) -- 2.47.3