[v5.15] general protection fault in __io_wq_cpu_online

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6e2fd6534337 Linux 5.15.213
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=16cae3b9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f161cbc9aef65db0
dashboard link: https://syzkaller.appspot.com/bug?extid=0afdefbae7480fcc0f36
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d7b46606b13d/disk-6e2fd653.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/da120fdeb081/vmlinux-6e2fd653.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3c2643457e3f/bzImage-6e2fd653.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0afdef...@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xdffffc0000000014: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x00000000000000a0-0x00000000000000a7]
CPU: 1 PID: 18 Comm: cpuhp/1 Tainted: G S syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:io_wq_for_each_worker io_uring/io-wq.c:860 [inline]
RIP: 0010:__io_wq_cpu_online+0x173/0x430 io_uring/io-wq.c:1326
Code: 8d 1c c1 48 89 d8 48 c1 e8 03 80 3c 28 00 74 08 48 89 df e8 ff ff d8 fd 4c 8b 23 b8 a0 00 00 00 49 01 c4 4c 89 e0 48 c1 e8 03 <80> 3c 28 00 74 08 4c 89 e7 e8 df ff d8 fd 4d 8b 2c 24 4d 39 e5 0f
RSP: 0018:ffffc90000d87c78 EFLAGS: 00010206
RAX: 0000000000000014 RBX: ffff8880730449a0 RCX: ffff888073044998
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000
RBP: dffffc0000000000 R08: dffffc0000000000 R09: 1ffffffff203dc18
R10: dffffc0000000000 R11: fffffbfff203dc19 R12: 00000000000000a0
R13: ffff88807db668a0 R14: 0000000000000002 R15: 0000000000000001
FS: 0000000000000000(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00002000000001c4 CR3: 000000000c08e000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
io_wq_cpu_offline+0x20/0x30 io_uring/io-wq.c:1342
cpuhp_invoke_callback+0x321/0x7e0 kernel/cpu.c:213
cpuhp_thread_fun+0x3b2/0x7f0 kernel/cpu.c:822
smpboot_thread_fn+0x520/0x990 kernel/smpboot.c:164
kthread+0x42e/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>
Modules linked in:
---[ end trace db3525175b27f312 ]---
RIP: 0010:io_wq_for_each_worker io_uring/io-wq.c:860 [inline]
RIP: 0010:__io_wq_cpu_online+0x173/0x430 io_uring/io-wq.c:1326
Code: 8d 1c c1 48 89 d8 48 c1 e8 03 80 3c 28 00 74 08 48 89 df e8 ff ff d8 fd 4c 8b 23 b8 a0 00 00 00 49 01 c4 4c 89 e0 48 c1 e8 03 <80> 3c 28 00 74 08 4c 89 e7 e8 df ff d8 fd 4d 8b 2c 24 4d 39 e5 0f
RSP: 0018:ffffc90000d87c78 EFLAGS: 00010206
RAX: 0000000000000014 RBX: ffff8880730449a0 RCX: ffff888073044998
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000
RBP: dffffc0000000000 R08: dffffc0000000000 R09: 1ffffffff203dc18
R10: dffffc0000000000 R11: fffffbfff203dc19 R12: 00000000000000a0
R13: ffff88807db668a0 R14: 0000000000000002 R15: 0000000000000001
FS: 0000000000000000(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00002000000001c4 CR3: 000000000c08e000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: 8d 1c c1 lea (%rcx,%rax,8),%ebx
3: 48 89 d8 mov %rbx,%rax
6: 48 c1 e8 03 shr $0x3,%rax
a: 80 3c 28 00 cmpb $0x0,(%rax,%rbp,1)
e: 74 08 je 0x18
10: 48 89 df mov %rbx,%rdi
13: e8 ff ff d8 fd call 0xfdd90017
18: 4c 8b 23 mov (%rbx),%r12
1b: b8 a0 00 00 00 mov $0xa0,%eax
20: 49 01 c4 add %rax,%r12
23: 4c 89 e0 mov %r12,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 80 3c 28 00 cmpb $0x0,(%rax,%rbp,1) <-- trapping instruction
2e: 74 08 je 0x38
30: 4c 89 e7 mov %r12,%rdi
33: e8 df ff d8 fd call 0xfdd90017
38: 4d 8b 2c 24 mov (%r12),%r13
3c: 4d 39 e5 cmp %r12,%r13
3f: 0f .byte 0xf


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