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Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1utYph-000000044XY-40Rl; Tue, 02 Sep 2025 21:46:30 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id C542730039F; Tue, 02 Sep 2025 23:46:28 +0200 (CEST) Date: Tue, 2 Sep 2025 23:46:28 +0200 From: Peter Zijlstra To: syzbot Cc: andrealmeid@igalia.com, dave@stgolabs.net, dvhart@infradead.org, linux-kernel@vger.kernel.org, mingo@redhat.com, syzkaller-bugs@googlegroups.com, tglx@linutronix.de, Sebastian Andrzej Siewior Subject: Re: [syzbot] [kernel?] general protection fault in try_to_wake_up (3) Message-ID: <20250902214628.GL4067720@noisy.programming.kicks-ass.net> References: <68b75989.050a0220.3db4df.01dd.GAE@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <68b75989.050a0220.3db4df.01dd.GAE@google.com> 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@syzkaller.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: > > __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