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* [syzbot] WARNING: suspicious RCU usage in __dev_queue_xmit
@ 2022-01-10 10:37 syzbot
  2022-01-10 11:48 ` Florian Westphal
  0 siblings, 1 reply; 2+ messages in thread
From: syzbot @ 2022-01-10 10:37 UTC (permalink / raw)
  To: a, alobakin, andrii, ast, atenart, b.a.t.m.a.n, bpf, coreteam,
	daniel, davem, fw, john.fastabend, jonathan.lemon, kadlec, kafai,
	kpsingh, kuba, linux-kernel, lukas, mareklindner, netdev,
	netfilter-devel, pablo, songliubraving, sven, sw, syzkaller-bugs,


syzbot found the following issue on:

HEAD commit:    4c375272fb0b Merge branch 'net-add-preliminary-netdev-refc..
git tree:       net-next
console output:
kernel config:
dashboard link:
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:
C reproducer:

The issue was bisected to:

commit 42df6e1d221dddc0f2acf2be37e68d553ad65f96
Author: Lukas Wunner <>
Date:   Fri Oct 8 20:06:03 2021 +0000

    netfilter: Introduce egress hook

bisection log:
final oops:
console output:

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Fixes: 42df6e1d221d ("netfilter: Introduce egress hook")

WARNING: suspicious RCU usage
5.16.0-rc3-syzkaller #0 Not tainted
include/linux/netfilter_netdev.h:97 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
3 locks held by kworker/u4:2/49:
 #0: ffff88814b0fe938 ((wq_completion)bat_events){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff88814b0fe938 ((wq_completion)bat_events){+.+.}-{0:0}, at: arch_atomic_long_set include/linux/atomic/atomic-long.h:41 [inline]
 #0: ffff88814b0fe938 ((wq_completion)bat_events){+.+.}-{0:0}, at: atomic_long_set include/linux/atomic/atomic-instrumented.h:1198 [inline]
 #0: ffff88814b0fe938 ((wq_completion)bat_events){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:635 [inline]
 #0: ffff88814b0fe938 ((wq_completion)bat_events){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:662 [inline]
 #0: ffff88814b0fe938 ((wq_completion)bat_events){+.+.}-{0:0}, at: process_one_work+0x896/0x1690 kernel/workqueue.c:2269
 #1: ffffc9000119fdb0 ((work_completion)(&(&forw_packet_aggr->delayed_work)->work)){+.+.}-{0:0}, at: process_one_work+0x8ca/0x1690 kernel/workqueue.c:2273
 #2: ffffffff8bb83b00 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x1e3/0x3640 net/core/dev.c:4036

stack backtrace:
CPU: 1 PID: 49 Comm: kworker/u4:2 Not tainted 5.16.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: bat_events batadv_iv_send_outstanding_bat_ogm_packet
Call Trace:
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 nf_hook_egress include/linux/netfilter_netdev.h:97 [inline]
 __dev_queue_xmit+0x2eac/0x3640 net/core/dev.c:4053
 batadv_send_skb_packet+0x4a9/0x5f0 net/batman-adv/send.c:108
 batadv_iv_ogm_send_to_if net/batman-adv/bat_iv_ogm.c:393 [inline]
 batadv_iv_ogm_emit net/batman-adv/bat_iv_ogm.c:421 [inline]
 batadv_iv_send_outstanding_bat_ogm_packet+0x6d7/0x8e0 net/batman-adv/bat_iv_ogm.c:1701
 process_one_work+0x9b2/0x1690 kernel/workqueue.c:2298
 worker_thread+0x658/0x11f0 kernel/workqueue.c:2445
 kthread+0x405/0x4f0 kernel/kthread.c:327
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

This report is generated by a bot. It may contain errors.
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For information about bisection process see:
syzbot can test patches for this issue, for details see:

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2022-01-10 10:37 [syzbot] WARNING: suspicious RCU usage in __dev_queue_xmit syzbot
2022-01-10 11:48 ` Florian Westphal

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