Re: [syzbot] [net?] WARNING: locking bug in finish_task_switch (3)

[syzbot <syzbot+b5ddc2aecb8d1b29c871@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING: locking bug in finish_task_switch

------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON(1)
WARNING: kernel/locking/lockdep.c:238 at hlock_class kernel/locking/lockdep.c:238 [inline], CPU#0: syz.1.35/6518
WARNING: kernel/locking/lockdep.c:238 at check_wait_context kernel/locking/lockdep.c:4895 [inline], CPU#0: syz.1.35/6518
WARNING: kernel/locking/lockdep.c:238 at __lock_acquire+0x584/0x2e50 kernel/locking/lockdep.c:5204, CPU#0: syz.1.35/6518
Modules linked in:
CPU: 0 UID: 0 PID: 6518 Comm: syz.1.35 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:hlock_class kernel/locking/lockdep.c:238 [inline]
RIP: 0010:check_wait_context kernel/locking/lockdep.c:4895 [inline]
RIP: 0010:__lock_acquire+0x58b/0x2e50 kernel/locking/lockdep.c:5204
Code: fa 18 00 74 04 31 c9 eb 2d 90 e8 c0 a1 36 03 85 c0 74 1c 83 3d a9 4a d7 0e 00 75 13 48 8d 3d 0c 53 da 0e 48 c7 c6 d9 e2 59 8e <67> 48 0f b9 3a 90 31 c9 48 8b 3c 24 0f b6 81 c4 00 00 00 84 c0 0f
RSP: 0000:ffffc90004146538 EFLAGS: 00010046
RAX: 0000000000000001 RBX: ffff8880315a4a78 RCX: ffff8880315a3e80
RDX: 0000000040000000 RSI: ffffffff8e59e2d9 RDI: ffffffff907d72f0
RBP: 0000000000000002 R08: ffffffff907a6a83 R09: 1ffffffff20f4d50
R10: dffffc0000000000 R11: fffffbfff20f4d51 R12: 0000000000000004
R13: 0000000000000000 R14: ffff8880315a4a80 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff888124cde000(0063) knlGS:00000000f67b3b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00000000f6834da4 CR3: 000000001c2ca000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908
 finish_lock_switch kernel/sched/core.c:5248 [inline]
 finish_task_switch+0x16e/0xc60 kernel/sched/core.c:5369
 context_switch kernel/sched/core.c:5523 [inline]
 __schedule+0x17dc/0x5820 kernel/sched/core.c:7270
 __schedule_loop kernel/sched/core.c:7347 [inline]
 schedule+0x164/0x2b0 kernel/sched/core.c:7362
 __lock_sock+0x162/0x2c0 net/core/sock.c:3235
 __lock_sock_fast+0x94/0xe0 net/core/sock.c:3897
 lock_sock_fast include/net/sock.h:1746 [inline]
 tcp_get_info+0x26d/0x2b70 net/ipv4/tcp.c:4250
 inet_sk_diag_fill+0xdb6/0x18c0 net/ipv4/inet_diag.c:330
 sk_diag_fill+0x2e6/0xd50 net/ipv4/tcp_diag.c:284
 tcp_diag_dump+0x1ba6/0x2020 net/ipv4/tcp_diag.c:538
 __inet_diag_dump net/ipv4/inet_diag.c:823 [inline]
 inet_diag_dump_compat+0x274/0x490 net/ipv4/inet_diag.c:927
 netlink_dump+0x711/0xee0 net/netlink/af_netlink.c:2331
 __netlink_dump_start+0x589/0x7b0 net/netlink/af_netlink.c:2446
 netlink_dump_start include/linux/netlink.h:341 [inline]
 inet_diag_rcv_msg_compat+0x214/0x420 net/ipv4/inet_diag.c:962
 sock_diag_rcv_msg+0x4b0/0x5f0 net/core/sock_diag.c:-1
 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:800
 __sock_sendmsg net/socket.c:815 [inline]
 ____sys_sendmsg+0x54e/0x850 net/socket.c:2713
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2767
 __sys_sendmsg+0x177/0x240 net/socket.c:2799
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
 __do_fast_syscall_32+0x27a/0x6a0 arch/x86/entry/syscall_32.c:291
 do_fast_syscall_32+0x33/0x70 arch/x86/entry/syscall_32.c:316
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf6fff0ec
Code: 90 85 d2 74 0a 89 ce 81 e6 ff 0f 00 00 89 32 85 c0 74 05 c1 e9 0c 89 08 31 c0 5e 5d c3 90 0f 1f 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 58 b8
RSP: 002b:00000000f67b350c EFLAGS: 00000206 ORIG_RAX: 0000000000000172
RAX: ffffffffffffffda RBX: 0000000000000008 RCX: 0000000080000240
RDX: 0000000004004010 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
----------------
Code disassembly (best guess):
   0:	fa                   	cli
   1:	18 00                	sbb    %al,(%rax)
   3:	74 04                	je     0x9
   5:	31 c9                	xor    %ecx,%ecx
   7:	eb 2d                	jmp    0x36
   9:	90                   	nop
   a:	e8 c0 a1 36 03       	call   0x336a1cf
   f:	85 c0                	test   %eax,%eax
  11:	74 1c                	je     0x2f
  13:	83 3d a9 4a d7 0e 00 	cmpl   $0x0,0xed74aa9(%rip)        # 0xed74ac3
  1a:	75 13                	jne    0x2f
  1c:	48 8d 3d 0c 53 da 0e 	lea    0xeda530c(%rip),%rdi        # 0xeda532f
  23:	48 c7 c6 d9 e2 59 8e 	mov    $0xffffffff8e59e2d9,%rsi
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	90                   	nop
  30:	31 c9                	xor    %ecx,%ecx
  32:	48 8b 3c 24          	mov    (%rsp),%rdi
  36:	0f b6 81 c4 00 00 00 	movzbl 0xc4(%rcx),%eax
  3d:	84 c0                	test   %al,%al
  3f:	0f                   	.byte 0xf


Tested on:

commit:         18fbf515 Merge tag 'mm-stable-2026-08-26-15-22' of git..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1115f7f9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a14b7fde441ba049
dashboard link: https://syzkaller.appspot.com/bug?extid=b5ddc2aecb8d1b29c871
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: i386

Note: no patches were applied.