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Message-ID: <20250902214628.GL4067720@noisy.programming.kicks-ass.net>
Date: Tue, 2 Sep 2025 23:46:28 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: syzbot <syzbot+034246a838a10d181e78@...kaller.appspotmail.com>
Cc: andrealmeid@...lia.com, dave@...olabs.net, dvhart@...radead.org,
linux-kernel@...r.kernel.org, mingo@...hat.com,
syzkaller-bugs@...glegroups.com, tglx@...utronix.de,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [syzbot] [kernel?] general protection fault in try_to_wake_up (3)
On Tue, Sep 02, 2025 at 01:54:33PM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 5c3b3264e585 Merge tag 'x86_urgent_for_v6.17_rc4' of git:/..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=12e1ae34580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=bd9738e00c1bbfb4
> dashboard link: https://syzkaller.appspot.com/bug?extid=034246a838a10d181e78
> 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=10f6a1f0580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/37953b384dff/disk-5c3b3264.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/df5cc1c4e51d/vmlinux-5c3b3264.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/2ed6195eae9f/bzImage-5c3b3264.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+034246a838a10d181e78@...kaller.appspotmail.com
>
> Oops: general protection fault, probably for non-canonical address 0xdffffc000000014b: 0000 [#1] SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000a58-0x0000000000000a5f]
When I build the provided .config with clang-20, that a58 offset is
exactly task_struct::pi_lock::lockdep_map, which nicely corresponds with
the below stacktrace, and seems to suggest someone did:
try_to_wake_up(NULL).
> CPU: 1 UID: 0 PID: 6293 Comm: syz.0.60 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
> RIP: 0010:kasan_byte_accessible+0x12/0x30 mm/kasan/generic.c:199
> Code: 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 66 0f 1f 00 48 c1 ef 03 48 b8 00 00 00 00 00 fc ff df <0f> b6 04 07 3c 08 0f 92 c0 e9 d0 9f dc 08 cc 66 66 66 66 66 66 2e
> RSP: 0018:ffffc9000157f7e0 EFLAGS: 00010006
> RAX: dffffc0000000000 RBX: ffffffff8af9dfe7 RCX: e1dbfc1ee2ae4a00
> RDX: 0000000000000000 RSI: ffffffff8af9dfe7 RDI: 000000000000014b
> RBP: ffffffff81908477 R08: 0000000000000001 R09: 0000000000000000
> R10: dffffc0000000000 R11: fffffbfff1e3a947 R12: 0000000000000000
> R13: 0000000000000a58 R14: 0000000000000a58 R15: 0000000000000001
> FS: 00007ff6ed61d6c0(0000) GS:ffff8881269c2000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ff6ed61cf40 CR3: 0000000027554000 CR4: 00000000003526f0
> Call Trace:
> <TASK>
> __kasan_check_byte+0x12/0x40 mm/kasan/common.c:567
> kasan_check_byte include/linux/kasan.h:399 [inline]
> lock_acquire+0x8d/0x360 kernel/locking/lockdep.c:5842
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0xa7/0xf0 kernel/locking/spinlock.c:162
> class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:557 [inline]
> try_to_wake_up+0x67/0x12b0 kernel/sched/core.c:4216
> requeue_pi_wake_futex+0x24b/0x2f0 kernel/futex/requeue.c:249
Trouble is, we've not changed the requeue bits in a fair while... So I'm
somewhat confused on how this happens now ?!
> futex_proxy_trylock_atomic kernel/futex/requeue.c:340 [inline]
> futex_requeue+0x135f/0x1870 kernel/futex/requeue.c:498
> do_futex+0x362/0x420 kernel/futex/syscalls.c:-1
> __do_sys_futex kernel/futex/syscalls.c:179 [inline]
> __se_sys_futex+0x36f/0x400 kernel/futex/syscalls.c:160
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
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