Subject: [syzbot] WARNING in cake_dequeue

From: syzbot <[email-masked]>
Date: Tue, 20 Sep 2022 10:22:42 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    521a547ced64 Linux 6.0-rc6
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1267c108880000
kernel config:  https://syzkaller.appspot.com/x/.config?x=122d7bd4fc8e0ecb
dashboard link: https://syzkaller.appspot.com/bug?extid=1a58ef288b4f7a56adbf
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

------------[ cut here ]------------
WARNING: CPU: 0 PID: 12003 at net/sched/sch_cake.c:2093 cake_dequeue+0x2188/0x3cb0 net/sched/sch_cake.c:2093
Modules linked in:
CPU: 0 PID: 12003 Comm: syz-executor.4 Not tainted 6.0.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
RIP: 0010:cake_dequeue+0x2188/0x3cb0 net/sched/sch_cake.c:2093
Code: 66 39 c5 0f 42 e8 e8 a7 a1 f1 f9 89 ee bf 00 04 00 00 e8 3b 9e f1 f9 66 81 fd 00 04 0f b7 dd 0f 86 a1 ef ff ff e8 88 a1 f1 f9 <0f> 0b e9 95 ef ff ff 31 ed e9 83 e8 ff ff e8 75 a1 f1 f9 48 8b 84
RSP: 0018:ffffc90000007cf0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 000000000000ffff RCX: 0000000000000100
RDX: ffff888033c15880 RSI: ffffffff878a6798 RDI: 0000000000000003
RBP: 000000000000ffff R08: 0000000000000003 R09: 0000000000000400
R10: 000000000000ffff R11: 0000000000000001 R12: 0000000000000001
R13: dffffc0000000000 R14: ffff88803ef01aa0 R15: ffff88803ef00000
FS:  0000000000000000(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2eb23000 CR3: 000000000bc8e000 CR4: 0000000000350ef0
Call Trace:
 <IRQ>
 dequeue_skb net/sched/sch_generic.c:292 [inline]
 qdisc_restart net/sched/sch_generic.c:397 [inline]
 __qdisc_run+0x1ae/0x1710 net/sched/sch_generic.c:415
 qdisc_run include/net/pkt_sched.h:126 [inline]
 qdisc_run include/net/pkt_sched.h:123 [inline]
 net_tx_action+0x71f/0xd20 net/core/dev.c:5086
 __do_softirq+0x1d3/0x9c6 kernel/softirq.c:571
 invoke_softirq kernel/softirq.c:445 [inline]
 __irq_exit_rcu+0x123/0x180 kernel/softirq.c:650
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:662
 sysvec_apic_timer_interrupt+0x93/0xc0 arch/x86/kernel/apic/apic.c:1106
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:649
RIP: 0010:check_kcov_mode kernel/kcov.c:166 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0xd/0x60 kernel/kcov.c:200
Code: 00 00 e9 86 c0 81 02 66 0f 1f 44 00 00 48 8b be a8 01 00 00 e8 b4 ff ff ff 31 c0 c3 90 65 8b 05 19 66 86 7e 89 c1 48 8b 34 24 <81> e1 00 01 00 00 65 48 8b 14 25 80 6f 02 00 a9 00 01 ff 00 74 0e
RSP: 0018:ffffc9000a98f758 EFLAGS: 00000246
RAX: 0000000080000001 RBX: 00007fee55929000 RCX: 0000000080000001
RDX: ffff888033c15880 RSI: ffffffff81b45ece RDI: 0000000000000001
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffea0001b5bac8
R13: ffffea0001b5bac0 R14: dffffc0000000000 R15: ffff888077a6a940
 zap_pte_range mm/memory.c:1508 [inline]
 zap_pmd_range mm/memory.c:1575 [inline]
 zap_pud_range mm/memory.c:1604 [inline]
 zap_p4d_range mm/memory.c:1625 [inline]
 unmap_page_range+0xd1e/0x3cc0 mm/memory.c:1646
 unmap_single_vma+0x196/0x360 mm/memory.c:1694
 unmap_vmas+0x18c/0x310 mm/memory.c:1731
 exit_mmap+0x1b8/0x490 mm/mmap.c:3116
 __mmput+0x122/0x4b0 kernel/fork.c:1187
 mmput+0x56/0x60 kernel/fork.c:1208
 exit_mm kernel/exit.c:510 [inline]
 do_exit+0x9e2/0x29b0 kernel/exit.c:782
 do_group_exit+0xd2/0x2f0 kernel/exit.c:925
 get_signal+0x238c/0x2610 kernel/signal.c:2857
 arch_do_signal_or_restart+0x82/0x2300 arch/x86/kernel/signal.c:869
 exit_to_user_mode_loop kernel/entry/common.c:166 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
 syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:294
 do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7fee55a89409
Code: Unable to access opcode bytes at RIP 0x7fee55a893df.
RSP: 002b:00007fee56bfb218 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007fee55b9bf88 RCX: 00007fee55a89409
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007fee55b9bf88
RBP: 00007fee55b9bf80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fee55b9bf8c
R13: 00007fffab12ee9f R14: 00007fee56bfb300 R15: 0000000000022000
 </TASK>
----------------
Code disassembly (best guess):
   0:	00 00                	add    %al,(%rax)
   2:	e9 86 c0 81 02       	jmpq   0x281c08d
   7:	66 0f 1f 44 00 00    	nopw   0x0(%rax,%rax,1)
   d:	48 8b be a8 01 00 00 	mov    0x1a8(%rsi),%rdi
  14:	e8 b4 ff ff ff       	callq  0xffffffcd
  19:	31 c0                	xor    %eax,%eax
  1b:	c3                   	retq
  1c:	90                   	nop
  1d:	65 8b 05 19 66 86 7e 	mov    %gs:0x7e866619(%rip),%eax        # 0x7e86663d
  24:	89 c1                	mov    %eax,%ecx
  26:	48 8b 34 24          	mov    (%rsp),%rsi
* 2a:	81 e1 00 01 00 00    	and    $0x100,%ecx <-- trapping instruction
  30:	65 48 8b 14 25 80 6f 	mov    %gs:0x26f80,%rdx
  37:	02 00
  39:	a9 00 01 ff 00       	test   $0xff0100,%eax
  3e:	74 0e                	je     0x4e

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