Re: [syzbot] [block?] general protection fault in blk_mq_free_tags_callback

[Jens Axboe <axboe@kernel.dk>]

On 9/22/25 2:24 PM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    846bd2225ec3 Add linux-next specific files for 20250919
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=13c238e2580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=135377594f35b576
> dashboard link: https://syzkaller.appspot.com/bug?extid=5c5d41e80248d610221f
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=155e427c580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17bb8142580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/c53d48022f8a/disk-846bd222.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/483534e784c8/vmlinux-846bd222.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/721b36eec9b3/bzImage-846bd222.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+5c5d41e80248d610221f@syzkaller.appspotmail.com
> 
> Oops: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
> CPU: 0 UID: 0 PID: 5962 Comm: kworker/0:3 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
> Workqueue: rcu_gp srcu_invoke_callbacks
> RIP: 0010:__list_del_entry_valid_or_report+0x25/0x190 lib/list_debug.c:49
> Code: 90 90 90 90 90 f3 0f 1e fa 41 57 41 56 41 55 41 54 53 48 89 fb 49 bd 00 00 00 00 00 fc ff df 48 83 c7 08 48 89 f8 48 c1 e8 03 <42> 80 3c 28 00 74 05 e8 af 58 47 fd 4c 8b 7b 08 48 89 d8 48 c1 e8
> RSP: 0018:ffffc90003d2f8e8 EFLAGS: 00010202
> RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffff88802f573c80
> RDX: 0000000000000000 RSI: 0000000000000200 RDI: 0000000000000008
> RBP: dffffc0000000000 R08: ffffffff8fe4db77 R09: 1ffffffff1fc9b6e
> R10: dffffc0000000000 R11: ffffffff84b089f0 R12: 1ffff11004cb1e1f
> R13: dffffc0000000000 R14: ffff88802658f0a0 R15: 0000000000000000
> FS:  0000000000000000(0000) GS:ffff8881257a2000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000055946acdc950 CR3: 000000007a708000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  __list_del_entry_valid include/linux/list.h:132 [inline]
>  __list_del_entry include/linux/list.h:223 [inline]
>  list_del_init include/linux/list.h:295 [inline]
>  blk_mq_free_tags_callback+0x5a/0x180 block/blk-mq-tag.c:593
>  srcu_invoke_callbacks+0x208/0x450 kernel/rcu/srcutree.c:1807
>  process_one_work kernel/workqueue.c:3263 [inline]
>  process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
>  worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
>  kthread+0x711/0x8a0 kernel/kthread.c:463
>  ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:__list_del_entry_valid_or_report+0x25/0x190 lib/list_debug.c:49
> Code: 90 90 90 90 90 f3 0f 1e fa 41 57 41 56 41 55 41 54 53 48 89 fb 49 bd 00 00 00 00 00 fc ff df 48 83 c7 08 48 89 f8 48 c1 e8 03 <42> 80 3c 28 00 74 05 e8 af 58 47 fd 4c 8b 7b 08 48 89 d8 48 c1 e8
> RSP: 0018:ffffc90003d2f8e8 EFLAGS: 00010202
> RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffff88802f573c80
> RDX: 0000000000000000 RSI: 0000000000000200 RDI: 0000000000000008
> RBP: dffffc0000000000 R08: ffffffff8fe4db77 R09: 1ffffffff1fc9b6e
> R10: dffffc0000000000 R11: ffffffff84b089f0 R12: 1ffff11004cb1e1f
> R13: dffffc0000000000 R14: ffff88802658f0a0 R15: 0000000000000000
> FS:  0000000000000000(0000) GS:ffff8881257a2000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000055946acdc950 CR3: 000000007a708000 CR4: 00000000003526f0
> ----------------
> Code disassembly (best guess):
>    0:	90                   	nop
>    1:	90                   	nop
>    2:	90                   	nop
>    3:	90                   	nop
>    4:	90                   	nop
>    5:	f3 0f 1e fa          	endbr64
>    9:	41 57                	push   %r15
>    b:	41 56                	push   %r14
>    d:	41 55                	push   %r13
>    f:	41 54                	push   %r12
>   11:	53                   	push   %rbx
>   12:	48 89 fb             	mov    %rdi,%rbx
>   15:	49 bd 00 00 00 00 00 	movabs $0xdffffc0000000000,%r13
>   1c:	fc ff df
>   1f:	48 83 c7 08          	add    $0x8,%rdi
>   23:	48 89 f8             	mov    %rdi,%rax
>   26:	48 c1 e8 03          	shr    $0x3,%rax
> * 2a:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1) <-- trapping instruction
>   2f:	74 05                	je     0x36
>   31:	e8 af 58 47 fd       	call   0xfd4758e5
>   36:	4c 8b 7b 08          	mov    0x8(%rbx),%r15
>   3a:	48 89 d8             	mov    %rbx,%rax
>   3d:	48                   	rex.W
>   3e:	c1                   	.byte 0xc1
>   3f:	e8                   	.byte 0xe8
> 
> 
> ---
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> 
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Adding Ming, looks related to the SRCU changes perhaps?

-- 
Jens Axboe