On Wed, Jul 29, 2020 at 02:23:15AM +0000, Xu Qiang wrote:
> A soft deadlock occurs when call hrtimer_cancel in softirq context:
>
> a) The main frequency of the machine is very slow
> b) output->period_ns is very small, even only 1 ns
>
> The problem can be solved in the following way: Setting a hrtimer exit flag
> in the vkms_disable_vblank function and checking the flag in the
> vkms_vblank_simulate function. If the flag is set, the hrtimer is not added
> to hrtimer queue again,the hrtimer_cancel function can exit quickly
> without deadlock.
>
> watchdog: BUG: soft lockup - CPU#2 stuck for 134s! [syz-executor.2:18027]
> Modules linked in:
> CPU: 2 PID: 18027 Comm: syz-executor.2 Tainted: G W 5.8.0-rc2-csan #2
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
> RIP: 0010:csd_lock_wait kernel/smp.c:108 [inline]
> RIP: 0010:smp_call_function_many_cond+0x40c/0x470 kernel/smp.c:555
> RSP: 0018:ffffc900028d3a88 EFLAGS: 00000297
> RAX: 0000000000000002 RBX: ffff888237cacc80 RCX: ffffffff813240fc
> RDX: 0000000000000001 RSI: 0000000000000000 RDI: 0000000000000005
> RBP: 0000000000000001 R08: ffff8881f497d000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000100 R12: ffff888237cf6fc0
> R13: 0000000000000003 R14: ffff888237cacc88 R15: 0000000000000001
> FS: 00007fa6314a9700(0000) GS:ffff888237c80000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000513c80 CR3: 00000001e3df3002 CR4: 00000000000626e0
> Call Trace:
> smp_call_function_many kernel/smp.c:577 [inline]
> smp_call_function+0x40/0x80 kernel/smp.c:599
> on_each_cpu+0x2a/0xc0 kernel/smp.c:717
> __purge_vmap_area_lazy+0x7c/0xbc0 mm/vmalloc.c:1367
> _vm_unmap_aliases.part.0+0x126/0x180 mm/vmalloc.c:1800
> _vm_unmap_aliases mm/vmalloc.c:1769 [inline]
> vm_unmap_aliases+0x2f/0x40 mm/vmalloc.c:1823
> change_page_attr_set_clr+0x10a/0x4a0 arch/x86/mm/pat/set_memory.c:1732
> change_page_attr_clear arch/x86/mm/pat/set_memory.c:1789 [inline]
> set_memory_ro+0x2b/0x40 arch/x86/mm/pat/set_memory.c:1935
> bpf_jit_binary_lock_ro include/linux/filter.h:815 [inline]
> bpf_int_jit_compile+0x54f/0x663 arch/x86/net/bpf_jit_comp.c:1929
> bpf_prog_select_runtime+0x1cc/0x2c0 kernel/bpf/core.c:1807
> bpf_migrate_filter net/core/filter.c:1264 [inline]
> bpf_prepare_filter net/core/filter.c:1312 [inline]
> bpf_prepare_filter+0x518/0x620 net/core/filter.c:1278
> __get_filter+0x107/0x160 net/core/filter.c:1481
> sk_attach_filter+0x19/0xa0 net/core/filter.c:1496
> sock_setsockopt+0x1208/0x1230 net/core/sock.c:1080
> __sys_setsockopt+0x248/0x270 net/socket.c:2123
> __do_sys_setsockopt net/socket.c:2143 [inline]
> __se_sys_setsockopt net/socket.c:2140 [inline]
> __x64_sys_setsockopt+0x22/0x30 net/socket.c:2140
> do_syscall_64+0x48/0xb0 arch/x86/entry/common.c:359
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> Sending NMI from CPU 2 to CPUs 0-1,3-5:
> NMI backtrace for cpu 4 skipped: idling at native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:60
> NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:60
> NMI backtrace for cpu 1
> NMI backtrace for cpu 3
> CPU: 3 PID: 0 Comm: swapper/3 Tainted: G W 5.8.0-rc2-csan #2
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
> RIP: 0010:preempt_count arch/x86/include/asm/preempt.h:26 [inline]
> RIP: 0010:preempt_count_sub+0xa/0x90 kernel/sched/core.c:3874
> RSP: 0018:ffffc9000012cdd0 EFLAGS: 00000046
> RAX: 0000000000000001 RBX: ffff88822ecb8fb0 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000086 RDI: 0000000000000001
> RBP: ffff888237d5edc0 R08: ffff888236ddc000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 00000000ffffffff
> R13: 0000000000000086 R14: ffff888237d5edc0 R15: ffffffff85bc6d60
> FS: 0000000000000000(0000) GS:ffff888237cc0000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f35cc47adb8 CR3: 0000000005a23006 CR4: 00000000000626e0
> Call Trace:
> <IRQ>
> __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
> _raw_spin_unlock_irqrestore+0x2f/0x50 kernel/locking/spinlock.c:191
> unlock_hrtimer_base kernel/time/hrtimer.c:898 [inline]
> hrtimer_try_to_cancel kernel/time/hrtimer.c:1171 [inline]
> hrtimer_try_to_cancel+0xbd/0x1b0 kernel/time/hrtimer.c:1151
> hrtimer_cancel+0x13/0x40 kernel/time/hrtimer.c:1278
> __disable_vblank drivers/gpu/drm/drm_vblank.c:429 [inline]
> drm_vblank_disable_and_save+0x122/0x140 drivers/gpu/drm/drm_vblank.c:470
> vblank_disable_fn+0x96/0xa0 drivers/gpu/drm/drm_vblank.c:487
> call_timer_fn+0x3a/0x230 kernel/time/timer.c:1404
> expire_timers kernel/time/timer.c:1449 [inline]
> __run_timers kernel/time/timer.c:1773 [inline]
> __run_timers kernel/time/timer.c:1740 [inline]
> run_timer_softirq+0x2b8/0x840 kernel/time/timer.c:1786
> __do_softirq+0x118/0x344 kernel/softirq.c:292
> asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:711
> </IRQ>
> __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
> run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
> do_softirq_own_stack+0x5a/0x70 arch/x86/kernel/irq_64.c:77
> invoke_softirq kernel/softirq.c:387 [inline]
> __irq_exit_rcu kernel/softirq.c:417 [inline]
> irq_exit_rcu+0xb1/0xd0 kernel/softirq.c:429
> sysvec_apic_timer_interrupt+0x42/0xd0 arch/x86/kernel/apic/apic.c:1091
> asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:596
> ------------[ cut here ]------------
> WARNING: CPU: 5 PID: 8121 at drivers/gpu/drm/vkms/vkms_crtc.c:21 vkms_vblank_simulate+0x19a/0x1b0 drivers/gpu/drm/vkms/vkms_crtc.c:21
> Modules linked in:
> CPU: 5 PID: 8121 Comm: syslog-ng Tainted: G W 5.8.0-rc2-csan #2
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
> RIP: 0010:vkms_vblank_simulate+0x19a/0x1b0 drivers/gpu/drm/vkms/vkms_crtc.c:21
> RSP: 0018:ffffc90000184ee8 EFLAGS: 00010046
> RAX: ffff88822864a080 RBX: ffff88822ecb8fb0 RCX: ffffffff826cd2b0
> RDX: 0000000080010000 RSI: ffffffff826cd40a RDI: 0000000000000007
> RBP: 00000000001f058d R08: ffff88822864a080 R09: 7fffffffffffffff
> R10: 0000000000000000 R11: 0000000000000000 R12: ffff88822ecb8630
> R13: 0000000000000000 R14: 0000017998a35917 R15: ffff888237d5ed80
> FS: 00007f8dcbde0700(0000) GS:ffff888237d40000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffffffff600400 CR3: 000000022575f002 CR4: 00000000000626e0
> Call Trace:
> <IRQ>
> __run_hrtimer kernel/time/hrtimer.c:1520 [inline]
> __hrtimer_run_queues+0x14c/0x410 kernel/time/hrtimer.c:1584
> hrtimer_interrupt+0x141/0x2c0 kernel/time/hrtimer.c:1646
> local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1080 [inline]
> __sysvec_apic_timer_interrupt+0x6e/0x170 arch/x86/kernel/apic/apic.c:1097
> asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:711
> </IRQ>
> __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
> run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
> sysvec_apic_timer_interrupt+0xa9/0xd0 arch/x86/kernel/apic/apic.c:1091
> asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:596
> RIP: 0010:con_should_update drivers/tty/vt/vt.c:291 [inline]
> RIP: 0010:do_con_write.part.0+0xad6/0xfa0 drivers/tty/vt/vt.c:2790
> ---[ end trace d6a6c6a9ecb73597 ]---
> NMI backtrace for cpu 5 skipped: idling at native_halt+0xd/0x10 arch/x86/include/asm/irqflags.h:66
>
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
> Signed-off-by: Xu Qiang <xuqiang36@xxxxxxxxxx>
> ---
> drivers/gpu/drm/vkms/vkms_crtc.c | 5 ++++-
> drivers/gpu/drm/vkms/vkms_drv.h | 1 +
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
> index ac85e17428f8..655294f11bb8 100644
> --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> @@ -49,7 +49,7 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
> DRM_DEBUG_DRIVER("Composer worker already queued\n");
> }
>
> - return HRTIMER_RESTART;
> + return output->hrtimer_exit ? HRTIMER_NORESTART : HRTIMER_RESTART;
Hm don't we need some locking for this? Or at least a bit of thought about
ordering and stuff, maybe a comment about what's going on. Or are we
covered already by a different lock (but then maybe the check here should
be moved, and a comment added about which spinlock protects this).
The other question: How did you even end up in here? I think the better
fix would be to make sure the mode we're setting is reasonable, i.e. maybe
a refresh rate between 10Hz and 1000Hz or so. Even slow machines should
then be able to stop the timer ... That would be a lot more reasonable
fix, refresh rate with just a few ns never happen on real displays :-)
Cheers, Daniel
> }
>
> static int vkms_enable_vblank(struct drm_crtc *crtc)
> @@ -66,6 +66,8 @@ static int vkms_enable_vblank(struct drm_crtc *crtc)
> out->period_ns = ktime_set(0, vblank->framedur_ns);
> hrtimer_start(&out->vblank_hrtimer, out->period_ns, HRTIMER_MODE_REL);
>
> + out->hrtimer_exit = false;
> +
> return 0;
> }
>
> @@ -73,6 +75,7 @@ static void vkms_disable_vblank(struct drm_crtc *crtc)
> {
> struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
>
> + out->hrtimer_exit = true;
> hrtimer_cancel(&out->vblank_hrtimer);
> }
>
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index f4036bb0b9a8..4d4323dc2cfd 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -65,6 +65,7 @@ struct vkms_output {
> struct drm_connector connector;
> struct hrtimer vblank_hrtimer;
> ktime_t period_ns;
> + bool hrtimer_exit;
> struct drm_pending_vblank_event *event;
> /* ordered wq for composer_work */
> struct workqueue_struct *composer_workq;
> --
> 2.25.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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