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AKwUvBwlxLNP6O1nWDL68K92ZMO0JThpTHO4xkoNHWkNqwnEzuXWicTlgmwjo5l+Kpwkui3ym3g=@vger.kernel.org X-Gm-Message-State: AFuF++k1fF9oe88XpoB8o/1z2ZRvaMC6HXicnZBnHnY40AQGPhehN3dN Lb44+WeVkmuHM+NCVdtjU6Z8ghJdiDsP5vXNQYMv9aVFZBraBEcM900+S7XADmVXW+XFj9stuSM bgWXpZQ== X-Received: from plce19.prod.google.com ([2002:a17:902:f1d3:b0:2d0:1fb4:d72e]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:ccd2:b0:2d8:d4d9:ce3b with SMTP id d9443c01a7336-2d8d4d9cf90mr243978445ad.22.1788189344726; Mon, 31 Aug 2026 08:15:44 -0700 (PDT) Date: Mon, 31 Aug 2026 08:15:44 -0700 In-Reply-To: <6a958cd4.a8e469d2.cbf3.561d.GAE@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <6a958cd4.a8e469d2.cbf3.561d.GAE@google.com> Message-ID: Subject: Re: [syzbot] [kvm?] INFO: task hung in kvm_gmem_release From: Sean Christopherson To: syzbot Cc: david@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="us-ascii" On Mon, Aug 31, 2026, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 08dbfad3f504 Merge tag 'for-linus' of git://git.kernel.org.. > git tree: upstream > console+strace: https://syzkaller.appspot.com/x/log.txt?x=12ee0349580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=5e4e3a0e188a497e > dashboard link: https://syzkaller.appspot.com/bug?extid=6895ff73d58c59e653ba > compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1153ee25580000 > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/ddff5719ec3b/disk-08dbfad3.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/4b5e39b20fa5/vmlinux-08dbfad3.xz > kernel image: https://storage.googleapis.com/syzbot-assets/eb1f70eed57f/bzImage-08dbfad3.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+6895ff73d58c59e653ba@syzkaller.appspotmail.com > > INFO: task syz.0.17:6104 blocked for more than 143 seconds. > Not tainted syzkaller #0 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:syz.0.17 state:D stack:25544 pid:6104 tgid:6104 ppid:5900 task_flags:0x400040 flags:0x00080003 > Call Trace: > > context_switch kernel/sched/core.c:5520 [inline] > __schedule+0x17d4/0x5820 kernel/sched/core.c:7270 > __schedule_loop kernel/sched/core.c:7347 [inline] > schedule+0x164/0x2b0 kernel/sched/core.c:7362 > schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7419 > __mutex_lock+0 > __mutex_lock_common kernel/locking/mutex.c:726 [inline] > __mutex_lock+0x7c1/0x1550 kernel/locking/mutex.c:821 > kvm_gmem_release+0xdf/0x3e0 virt/kvm/guest_memfd.c:310 > __fput+0x418/0xa50 fs/file_table.c:512 > task_work_run+0x1d9/0x270 kernel/task_work.c:233 > ptrace_notify+0x27c/0x2b0 kernel/signal.c:2524 > ptrace_report_syscall include/linux/ptrace.h:416 [inline] > ptrace_report_syscall_exit+0x2d/0x50 include/linux/ptrace.h:477 > arch_ptrace_report_syscall_exit include/linux/entry-common.h:233 [inline] > syscall_exit_work include/linux/entry-common.h:266 [inline] > syscall_exit_to_user_mode_work include/linux/entry-common.h:297 [inline] > syscall_exit_to_user_mode include/linux/entry-common.h:334 [inline] > do_syscall_64+0x4a0/0x520 arch/x86/entry/syscall_64.c:89 > entry_SYSCALL_64_after_hwframe+0x77/0x7f ... > CPU: 1 UID: 0 PID: 16 Comm: pr/ttyS0 Not tainted syzkaller #0 PREEMPT(full) > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 > RIP: 0010:io_serial_in+0x77/0xc0 drivers/tty/serial/8250/8250_port.c:409 > Code: e8 4e e8 55 fc 44 89 f9 d3 e3 49 83 c6 40 4c 89 f0 48 c1 e8 03 42 80 3c 20 00 74 08 4c 89 f7 e8 1f b0 c5 fc 41 03 1e 89 da ec <0f> b6 c0 5b 41 5c 41 5e 41 5f e9 5a cc 74 06 cc 44 89 f9 80 e1 07 > RSP: 0018:ffffc900001578b8 EFLAGS: 00000002 > RAX: 1ffffffff35a5e00 RBX: 00000000000003fd RCX: 0000000000000000 > RDX: 00000000000003fd RSI: 0000000000000000 RDI: 0000000000000020 > RBP: dffffc0000000000 R08: 0000000000000003 R09: 0000000000000004 > R10: dffffc0000000000 R11: ffffffff8571cb00 R12: dffffc0000000000 > R13: 0000000000000000 R14: ffffffff9ad2f0c0 R15: 0000000000000000 > FS: 0000000000000000(0000) GS:ffff888124ddc000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000557adc994a38 CR3: 00000000772ec000 CR4: 00000000003526f0 > Call Trace: > > serial_in drivers/tty/serial/8250/8250.h:128 [inline] > serial_lsr_in drivers/tty/serial/8250/8250.h:150 [inline] > wait_for_lsr+0x184/0x2f0 drivers/tty/serial/8250/8250_port.c:2013 > serial8250_fifo_wait_for_lsr_thre drivers/tty/serial/8250/8250_port.c:3270 [inline] > __serial8250_console_fifo_write+0xcd/0x3e0 drivers/tty/serial/8250/8250_port.c:3345 > serial8250_console_fifo_write drivers/tty/serial/8250/8250_port.c:3378 [inline] > __serial8250_console_write drivers/tty/serial/8250/8250_port.c:3429 [inline] > serial8250_console_write+0xaa1/0x1200 drivers/tty/serial/8250/8250_port.c:3493 > nbcon_emit_next_record+0xef5/0x1a90 kernel/printk/nbcon.c:-1 > nbcon_emit_one kernel/printk/nbcon.c:1157 [inline] > nbcon_kthread_func+0x679/0x880 kernel/printk/nbcon.c:1271 > kthread+0x38b/0x480 kernel/kthread.c:436 > ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 > Marking this invalid, as I'm 99.9% certain guest_memfd is an innocent bystander. CPU1 is stuck on an IN instruction (the actual port I/O), and there are a handful of identical failures in random subsystems that pop up a few times a month[*]. My guess is the host side of the serial port is going out to lunch intermittently. [*] https://lore.kernel.org/all/?q=%22io_serial_in%22%20syzkaller #syz invalid