Commit 26f29b14 authored by Eric Dumazet's avatar Eric Dumazet Committed by Paolo Abeni
Browse files

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:
 <TASK>
  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: 27a01c19 ("net: fully inline backlog_unlock_irq_restore()")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260213120427.2914544-1-edumazet@google.com


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent 636fd32d

net/core/dev.c

+12 −5
Original line number Diff line number Diff line
@@ -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)
@@ -248,10 +251,14 @@ 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_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)

{