=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
net/sched/sch_api.c:304 suspicious rcu_dereference_protected() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
6 locks held by syz.2.1388/10384:
#0: ffff8880169e6460 (sb_writers#3){.+.+}-{0:0}, at: vfs_write+0x28a/0xd00 fs/read_write.c:590
#1: ffff88805155f268 (&sb->s_type->i_mutex_key#8){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:787 [inline]
#1: ffff88805155f268 (&sb->s_type->i_mutex_key#8){+.+.}-{3:3}, at: generic_file_write_iter+0x7e/0x1b0 mm/filemap.c:3941
#2: ffffffff8c11c460 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
#3: ffff88814bd2e948 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x6bc/0x870 net/core/dev.c:5128
#4: ffff88814bd2e908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
#4: ffff88814bd2e908 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x305/0x4a0 net/sched/sch_generic.c:354
#5: ffffffff8c11c460 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311
stack backtrace:
CPU: 0 PID: 10384 Comm: syz.2.1388 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
qdisc_lookup+0xa6/0x650 net/sched/sch_api.c:304
qdisc_tree_reduce_backlog+0x190/0x430 net/sched/sch_api.c:793
cake_dequeue+0x1b8f/0x4aa0 net/sched/sch_cake.c:2199
qdisc_peek_dequeued+0x6e/0x1f0 include/net/sch_generic.h:1115
tbf_dequeue+0x7d/0xce0 net/sched/sch_tbf.c:265
dequeue_skb net/sched/sch_generic.c:292 [inline]
qdisc_restart net/sched/sch_generic.c:397 [inline]
__qdisc_run+0x237/0x1480 net/sched/sch_generic.c:415
qdisc_run+0x103/0x2f0 include/net/pkt_sched.h:132
net_tx_action+0x6bc/0x870 net/core/dev.c:5128
handle_softirqs+0x328/0x820 kernel/softirq.c:576
__do_softirq kernel/softirq.c:610 [inline]
invoke_softirq kernel/softirq.c:450 [inline]
__irq_exit_rcu+0x12f/0x220 kernel/softirq.c:659
irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:unwind_get_return_address+0x52/0x80 arch/x86/kernel/unwind_orc.c:323
Code: 83 c3 48 49 89 df 49 c1 ef 03 43 80 3c 37 00 74 08 48 89 df e8 5f b9 87 00 48 8b 3b e8 57 66 1a 00 85 c0 74 14 43 80 3c 37 00 <74> 08 48 89 df e8 44 b9 87 00 48 8b 03 eb 02 31 c0 5b 41 5e 41 5f
RSP: 0018:ffffc90002feef88 EFLAGS: 00000246
RAX: 0000000000000001 RBX: ffffc90002feeff0 RCX: 0000000080000001
RDX: ffffc90002feef01 RSI: ffffc90002fef610 RDI: ffffffff81a534d7
RBP: ffffc90002fef030 R08: dffffc0000000000 R09: ffffc90002feeff8
R10: fffff520005fde01 R11: 1ffff920005fddff R12: ffff88807a9a3b80
R13: 1ffff920005fde20 R14: dffffc0000000000 R15: 1ffff920005fddfe
arch_stack_walk+0xf2/0x140 arch/x86/kernel/stacktrace.c:26
stack_trace_save+0x98/0xe0 kernel/stacktrace.c:122
save_stack+0xf3/0x1e0 mm/page_owner.c:119
__set_page_owner+0x41/0x2d0 mm/page_owner.c:181
prep_new_page mm/page_alloc.c:2426 [inline]
get_page_from_freelist+0x1b77/0x1c60 mm/page_alloc.c:4192
__alloc_pages+0x1e1/0x470 mm/page_alloc.c:5487
alloc_pages_vma+0x393/0x7c0 mm/mempolicy.c:2146
shmem_alloc_page mm/shmem.c:1586 [inline]
shmem_alloc_and_acct_page+0x427/0xb70 mm/shmem.c:1611
shmem_getpage_gfp+0x14f4/0x2d40 mm/shmem.c:1906
shmem_getpage mm/shmem.c:151 [inline]
shmem_write_begin+0xcd/0x1a0 mm/shmem.c:2474
generic_perform_write+0x2aa/0x530 mm/filemap.c:3785
__generic_file_write_iter+0x25f/0x4e0 mm/filemap.c:3912
generic_file_write_iter+0xa6/0x1b0 mm/filemap.c:3944
call_write_iter include/linux/fs.h:2172 [inline]
new_sync_write fs/read_write.c:507 [inline]
vfs_write+0x712/0xd00 fs/read_write.c:594
ksys_write+0x14d/0x250 fs/read_write.c:647
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f659f62869f
Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 f9 92 02 00 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 4c 93 02 00 48
RSP: 002b:00007f659d890df0 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000001000000 RCX: 00007f659f62869f
RDX: 0000000001000000 RSI: 00007f6595471000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000009654
R10: 0000000000000002 R11: 0000000000000293 R12: 0000000000000003
R13: 00007f659d890ef0 R14: 00007f659d890eb0 R15: 00007f6595471000
----------------
Code disassembly (best guess):
0: 83 c3 48 add $0x48,%ebx
3: 49 89 df mov %rbx,%r15
6: 49 c1 ef 03 shr $0x3,%r15
a: 43 80 3c 37 00 cmpb $0x0,(%r15,%r14,1)
f: 74 08 je 0x19
11: 48 89 df mov %rbx,%rdi
14: e8 5f b9 87 00 call 0x87b978
19: 48 8b 3b mov (%rbx),%rdi
1c: e8 57 66 1a 00 call 0x1a6678
21: 85 c0 test %eax,%eax
23: 74 14 je 0x39
25: 43 80 3c 37 00 cmpb $0x0,(%r15,%r14,1)
* 2a: 74 08 je 0x34 <-- trapping instruction
2c: 48 89 df mov %rbx,%rdi
2f: e8 44 b9 87 00 call 0x87b978
34: 48 8b 03 mov (%rbx),%rax
37: eb 02 jmp 0x3b
39: 31 c0 xor %eax,%eax
3b: 5b pop %rbx
3c: 41 5e pop %r14
3e: 41 5f pop %r15