Message-ID: <20250826021633.5550-1-hdanton@sina.com>
Date: Tue, 26 Aug 2025 10:16:20 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+e0930cb581675ca1c2e5@...kaller.appspotmail.com>
Cc: airlied@...il.com,
	linux-kernel@...r.kernel.org,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [dri?] possible deadlock in drm_vblank_disable_and_save

> Date: Mon, 25 Aug 2025 11:01:46 -0700
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    c330cb607721 Merge tag 'i2c-for-6.17-rc3' of git://git.ker..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15069862580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e1e1566c7726877e
> dashboard link: https://syzkaller.appspot.com/bug?extid=e0930cb581675ca1c2e5
> compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1660ec42580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11f8aef0580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/e3c902f92d1e/disk-c330cb60.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/bb0ab44f7737/vmlinux-c330cb60.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/6c8baacf629b/bzImage-c330cb60.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+e0930cb581675ca1c2e5@...kaller.appspotmail.com
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> syzkaller #0 Not tainted
> ------------------------------------------------------
> syz.0.184/6534 is trying to acquire lock:
> ffff8880b8923d90 ((softirq_ctrl.lock)){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline]
> ffff8880b8923d90 ((softirq_ctrl.lock)){+.+.}-{3:3}, at: __local_bh_disable_ip+0x264/0x400 kernel/softirq.c:168
> 
> but task is already holding lock:
> ffff8880242183a0 (&dev->vblank_time_lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline]
> ffff8880242183a0 (&dev->vblank_time_lock){+.+.}-{3:3}, at: drm_vblank_disable_and_save+0x7f/0x380 drivers/gpu/drm/drm_vblank.c:463
> 
> which lock already depends on the new lock.
> 
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #4 (&dev->vblank_time_lock){+.+.}-{3:3}:
>        lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
>        rt_spin_lock+0x88/0x2c0 kernel/locking/spinlock_rt.c:56
>        spin_lock include/linux/spinlock_rt.h:44 [inline]
>        drm_reset_vblank_timestamp drivers/gpu/drm/drm_vblank.c:246 [inline]
>        drm_crtc_vblank_on_config+0x2cd/0x860 drivers/gpu/drm/drm_vblank.c:1504
>        drm_crtc_vblank_on+0x88/0xc0 drivers/gpu/drm/drm_vblank.c:1535
>        crtc_enable drivers/gpu/drm/drm_atomic_helper.c:1610 [inline]
>        drm_atomic_helper_commit_modeset_enables+0x602/0xe10 drivers/gpu/drm/drm_atomic_helper.c:1680
>        vkms_atomic_commit_tail+0x69/0x210 drivers/gpu/drm/vkms/vkms_drv.c:65
>        commit_tail+0x281/0x3a0 drivers/gpu/drm/drm_atomic_helper.c:1986
>        drm_atomic_helper_commit+0xa6b/0xb10 drivers/gpu/drm/drm_atomic_helper.c:2226
>        drm_atomic_commit+0x262/0x2c0 drivers/gpu/drm/drm_atomic.c:1577
>        drm_client_modeset_commit_atomic+0x620/0x760 drivers/gpu/drm/drm_client_modeset.c:1103
>        drm_client_modeset_commit_locked+0xce/0x4d0 drivers/gpu/drm/drm_client_modeset.c:1206
>        drm_client_modeset_commit+0x4a/0x70 drivers/gpu/drm/drm_client_modeset.c:1232
>        __drm_fb_helper_restore_fbdev_mode_unlocked+0x9d/0x1b0 drivers/gpu/drm/drm_fb_helper.c:238
>        drm_fb_helper_set_par+0xaf/0x100 drivers/gpu/drm/drm_fb_helper.c:1360
>        fbcon_init+0x1255/0x2370 drivers/video/fbdev/core/fbcon.c:1130
>        visual_init+0x2ef/0x650 drivers/tty/vt/vt.c:1019
>        do_bind_con_driver+0x890/0xf70 drivers/tty/vt/vt.c:3915
>        do_take_over_console+0x899/0xa10 drivers/tty/vt/vt.c:4481
>        do_fbcon_takeover+0x118/0x200 drivers/video/fbdev/core/fbcon.c:565
>        do_fb_registered drivers/video/fbdev/core/fbcon.c:3008 [inline]
>        fbcon_fb_registered+0x35e/0x610 drivers/video/fbdev/core/fbcon.c:3028
>        do_register_framebuffer drivers/video/fbdev/core/fbmem.c:512 [inline]
>        register_framebuffer+0x70f/0x890 drivers/video/fbdev/core/fbmem.c:578
>        __drm_fb_helper_initial_config_and_unlock+0x130a/0x18a0 drivers/gpu/drm/drm_fb_helper.c:1852
>        drm_fbdev_client_hotplug+0x16f/0x230 drivers/gpu/drm/clients/drm_fbdev_client.c:52
>        drm_client_register+0x16f/0x210 drivers/gpu/drm/drm_client.c:141
>        drm_fbdev_client_setup+0x19f/0x3f0 drivers/gpu/drm/clients/drm_fbdev_client.c:159
>        drm_client_setup+0x10a/0x230 drivers/gpu/drm/clients/drm_client_setup.c:46
>        vkms_create drivers/gpu/drm/vkms/vkms_drv.c:201 [inline]
>        vkms_init+0x3e0/0x4b0 drivers/gpu/drm/vkms/vkms_drv.c:221
>        do_one_initcall+0x233/0x820 init/main.c:1269
>        do_initcall_level+0x104/0x190 init/main.c:1331
>        do_initcalls+0x59/0xa0 init/main.c:1347
>        kernel_init_freeable+0x334/0x4b0 init/main.c:1579
>        kernel_init+0x1d/0x1d0 init/main.c:1469
>        ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
>        ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
> 
> -> #3 (&dev->vbl_lock){+.+.}-{3:3}:
>        lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
>        rt_spin_lock+0x88/0x2c0 kernel/locking/spinlock_rt.c:56
>        spin_lock include/linux/spinlock_rt.h:44 [inline]
>        vblank_disable_fn+0x72/0x190 drivers/gpu/drm/drm_vblank.c:496
>        call_timer_fn+0x17b/0x5f0 kernel/time/timer.c:1747
>        expire_timers kernel/time/timer.c:1798 [inline]
>        __run_timers kernel/time/timer.c:2372 [inline]
>        __run_timer_base+0x648/0x970 kernel/time/timer.c:2384
>        run_timer_base kernel/time/timer.c:2393 [inline]
>        run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2403
>        handle_softirqs+0x22c/0x710 kernel/softirq.c:579
>        __do_softirq kernel/softirq.c:613 [inline]
>        run_ktimerd+0xcf/0x190 kernel/softirq.c:1043
>        smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160
>        kthread+0x711/0x8a0 kernel/kthread.c:463
>        ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
>        ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
> 
> -> #2 ((&vblank->disable_timer)){+...}-{0:0}:
>        lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
>        call_timer_fn+0xdb/0x5f0 kernel/time/timer.c:1744
>        expire_timers kernel/time/timer.c:1798 [inline]
>        __run_timers kernel/time/timer.c:2372 [inline]
>        __run_timer_base+0x648/0x970 kernel/time/timer.c:2384
>        run_timer_base kernel/time/timer.c:2393 [inline]
>        run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2403
>        handle_softirqs+0x22c/0x710 kernel/softirq.c:579
>        __do_softirq kernel/softirq.c:613 [inline]
>        run_ktimerd+0xcf/0x190 kernel/softirq.c:1043
>        smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160
>        kthread+0x711/0x8a0 kernel/kthread.c:463
>        ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
>        ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
> 
> -> #1 (&base->expiry_lock){+...}-{3:3}:
>        lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
>        rt_spin_lock+0x88/0x2c0 kernel/locking/spinlock_rt.c:56
>        spin_lock include/linux/spinlock_rt.h:44 [inline]
>        timer_base_lock_expiry kernel/time/timer.c:1501 [inline]
>        __run_timer_base+0x114/0x970 kernel/time/timer.c:2382
>        run_timer_base kernel/time/timer.c:2393 [inline]
>        run_timer_softirq+0x67/0x180 kernel/time/timer.c:2401
>        handle_softirqs+0x22c/0x710 kernel/softirq.c:579
>        __do_softirq kernel/softirq.c:613 [inline]
>        run_ktimerd+0xcf/0x190 kernel/softirq.c:1043
>        smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160
>        kthread+0x711/0x8a0 kernel/kthread.c:463
>        ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
>        ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
> 
This report is false positive as hrtimer has no dependence on timer.

> -> #0 ((softirq_ctrl.lock)){+.+.}-{3:3}:
>        check_prev_add kernel/locking/lockdep.c:3165 [inline]
>        check_prevs_add kernel/locking/lockdep.c:3284 [inline]
>        validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
>        __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
>        reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5385
>        __lock_release kernel/locking/lockdep.c:5574 [inline]
>        lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5889
>        __local_bh_enable_ip+0x10c/0x270 kernel/softirq.c:228
>        hrtimer_cancel+0x39/0x60 kernel/time/hrtimer.c:1491
>        __disable_vblank drivers/gpu/drm/drm_vblank.c:442 [inline]
>        drm_vblank_disable_and_save+0x1bc/0x380 drivers/gpu/drm/drm_vblank.c:481
>        drm_crtc_vblank_off+0x22e/0x820 drivers/gpu/drm/drm_vblank.c:1364
>        crtc_disable drivers/gpu/drm/drm_atomic_helper.c:1258 [inline]
>        disable_outputs drivers/gpu/drm/drm_atomic_helper.c:1340 [inline]
>        drm_atomic_helper_commit_modeset_disables+0xc89/0x2010 drivers/gpu/drm/drm_atomic_helper.c:1524
>        vkms_atomic_commit_tail+0x51/0x210 drivers/gpu/drm/vkms/vkms_drv.c:61
>        commit_tail+0x281/0x3a0 drivers/gpu/drm/drm_atomic_helper.c:1986
>        drm_atomic_helper_commit+0xa6b/0xb10 drivers/gpu/drm/drm_atomic_helper.c:2226
>        drm_atomic_commit+0x262/0x2c0 drivers/gpu/drm/drm_atomic.c:1577
>        drm_atomic_helper_set_config+0xe2/0x160 drivers/gpu/drm/drm_atomic_helper.c:3426
>        drm_mode_setcrtc+0x9a4/0x1c50 drivers/gpu/drm/drm_crtc.c:869
>        drm_ioctl_kernel+0x2d2/0x3a0 drivers/gpu/drm/drm_ioctl.c:796
>        drm_ioctl+0x685/0xb20 drivers/gpu/drm/drm_ioctl.c:893
>        vfs_ioctl fs/ioctl.c:51 [inline]
>        __do_sys_ioctl fs/ioctl.c:598 [inline]
>        __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
>        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
> 
> other info that might help us debug this:
> 
> Chain exists of:
>   (softirq_ctrl.lock) --> &dev->vbl_lock --> &dev->vblank_time_lock
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(&dev->vblank_time_lock);
>                                lock(&dev->vbl_lock);
>                                lock(&dev->vblank_time_lock);
>   lock((softirq_ctrl.lock));
> 
>  *** DEADLOCK ***
> 
> 8 locks held by syz.0.184/6534:
>  #0: ffffc900052d7b20 (crtc_ww_class_acquire){+.+.}-{0:0}, at: drm_mode_setcrtc+0x555/0x1c50 drivers/gpu/drm/drm_crtc.c:730
>  #1: ffffc900052d7b48 (crtc_ww_class_mutex){+.+.}-{4:4}, at: drm_mode_setcrtc+0x555/0x1c50 drivers/gpu/drm/drm_crtc.c:730
>  #2: ffff8880242184b8 (&dev->event_lock){+.+.}-{3:3}, at: spin_lock_irq include/linux/spinlock_rt.h:93 [inline]
>  #2: ffff8880242184b8 (&dev->event_lock){+.+.}-{3:3}, at: drm_crtc_vblank_off+0xe4/0x820 drivers/gpu/drm/drm_vblank.c:1355
>  #3: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
>  #3: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
>  #3: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
>  #3: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1bb/0x2c0 kernel/locking/spinlock_rt.c:57
>  #4: ffff888024218420 (&dev->vbl_lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline]
>  #4: ffff888024218420 (&dev->vbl_lock){+.+.}-{3:3}, at: drm_crtc_vblank_off+0xf5/0x820 drivers/gpu/drm/drm_vblank.c:1357
>  #5: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
>  #5: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
>  #5: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
>  #5: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1bb/0x2c0 kernel/locking/spinlock_rt.c:57
>  #6: ffff8880242183a0 (&dev->vblank_time_lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline]
>  #6: ffff8880242183a0 (&dev->vblank_time_lock){+.+.}-{3:3}, at: drm_vblank_disable_and_save+0x7f/0x380 drivers/gpu/drm/drm_vblank.c:463
>  #7: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
>  #7: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
>  #7: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
>  #7: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1bb/0x2c0 kernel/locking/spinlock_rt.c:57
> 
> stack backtrace:
> CPU: 1 UID: 0 PID: 6534 Comm: syz.0.184 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
>  print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
>  check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175
>  check_prev_add kernel/locking/lockdep.c:3165 [inline]
>  check_prevs_add kernel/locking/lockdep.c:3284 [inline]
>  validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
>  __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
>  reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5385
>  __lock_release kernel/locking/lockdep.c:5574 [inline]
>  lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5889
>  __local_bh_enable_ip+0x10c/0x270 kernel/softirq.c:228
>  hrtimer_cancel+0x39/0x60 kernel/time/hrtimer.c:1491
>  __disable_vblank drivers/gpu/drm/drm_vblank.c:442 [inline]
>  drm_vblank_disable_and_save+0x1bc/0x380 drivers/gpu/drm/drm_vblank.c:481
>  drm_crtc_vblank_off+0x22e/0x820 drivers/gpu/drm/drm_vblank.c:1364
>  crtc_disable drivers/gpu/drm/drm_atomic_helper.c:1258 [inline]
>  disable_outputs drivers/gpu/drm/drm_atomic_helper.c:1340 [inline]
>  drm_atomic_helper_commit_modeset_disables+0xc89/0x2010 drivers/gpu/drm/drm_atomic_helper.c:1524
>  vkms_atomic_commit_tail+0x51/0x210 drivers/gpu/drm/vkms/vkms_drv.c:61
>  commit_tail+0x281/0x3a0 drivers/gpu/drm/drm_atomic_helper.c:1986
>  drm_atomic_helper_commit+0xa6b/0xb10 drivers/gpu/drm/drm_atomic_helper.c:2226
>  drm_atomic_commit+0x262/0x2c0 drivers/gpu/drm/drm_atomic.c:1577
>  drm_atomic_helper_set_config+0xe2/0x160 drivers/gpu/drm/drm_atomic_helper.c:3426
>  drm_mode_setcrtc+0x9a4/0x1c50 drivers/gpu/drm/drm_crtc.c:869
>  drm_ioctl_kernel+0x2d2/0x3a0 drivers/gpu/drm/drm_ioctl.c:796
>  drm_ioctl+0x685/0xb20 drivers/gpu/drm/drm_ioctl.c:893
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:598 [inline]
>  __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
>  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
> RIP: 0033:0x7fcd2143ebe9
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fcd20a85038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007fcd21666090 RCX: 00007fcd2143ebe9
> RDX: 0000200000000740 RSI: 00000000c06864a2 RDI: 0000000000000003
> RBP: 00007fcd214c1e19 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fcd21666128 R14: 00007fcd21666090 R15: 00007ffd85f10678
>  </TASK>
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
> 
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup
> 

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