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Message-ID: <68aca50a.a00a0220.33401d.0441.GAE@google.com>
Date: Mon, 25 Aug 2025 11:01:46 -0700
From: syzbot <syzbot+e0930cb581675ca1c2e5@...kaller.appspotmail.com>
To: airlied@...il.com, dri-devel@...ts.freedesktop.org,
hamohammed.sa@...il.com, linux-kernel@...r.kernel.org,
louis.chauvet@...tlin.com, maarten.lankhorst@...ux.intel.com,
melissa.srw@...il.com, mripard@...nel.org, simona@...ll.ch,
syzkaller-bugs@...glegroups.com, tzimmermann@...e.de
Subject: [syzbot] [dri?] possible deadlock in drm_vblank_disable_and_save
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
-> #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:
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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:
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If you want to overwrite report's subsystems, reply with:
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