Am 11.07.23 um 11:31 schrieb Chen, Guchun:
[Public]
-----Original Message-----
From: Christian König<[email protected]>
Sent: Tuesday, July 11, 2023 5:23 PM
To: Chen, Guchun<[email protected]>; amd-
[email protected]; Deucher, Alexander
<[email protected]>; Zhang, Hawking
<[email protected]>; Koenig, Christian
<[email protected]>; Milinkovic, Dusica
<[email protected]>; Prica, Nikola<[email protected]>; Cui,
Flora<[email protected]>
Cc:[email protected]
Subject: Re: [PATCH v3] drm/amdgpu/vkms: relax timer deactivation by
hrtimer_try_to_cancel
Am 11.07.23 um 11:15 schrieb Chen, Guchun:
[Public]
-----Original Message-----
From: Christian König<[email protected]>
Sent: Tuesday, July 11, 2023 5:09 PM
To: Chen, Guchun<[email protected]>; amd-
[email protected]; Deucher, Alexander
<[email protected]>; Zhang, Hawking
<[email protected]>;
Koenig, Christian<[email protected]>; Milinkovic, Dusica
<[email protected]>; Prica, Nikola<[email protected]>;
Cui, Flora<[email protected]>
Cc:[email protected]
Subject: Re: [PATCH v3] drm/amdgpu/vkms: relax timer deactivation by
hrtimer_try_to_cancel
Am 11.07.23 um 03:38 schrieb Guchun Chen:
In below thousands of screen rotation loop tests with virtual
display enabled, a CPU hard lockup issue may happen, leading system
to unresponsive and crash.
do {
xrandr --output Virtual --rotate inverted
xrandr --output Virtual --rotate right
xrandr --output Virtual --rotate left
xrandr --output Virtual --rotate normal } while (1);
NMI watchdog: Watchdog detected hard LOCKUP on cpu 1
? hrtimer_run_softirq+0x140/0x140
? store_vblank+0xe0/0xe0 [drm]
hrtimer_cancel+0x15/0x30
amdgpu_vkms_disable_vblank+0x15/0x30 [amdgpu]
drm_vblank_disable_and_save+0x185/0x1f0 [drm]
drm_crtc_vblank_off+0x159/0x4c0 [drm] ?
record_print_text.cold+0x11/0x11 ?
wait_for_completion_timeout+0x232/0x280
? drm_crtc_wait_one_vblank+0x40/0x40 [drm] ?
bit_wait_io_timeout+0xe0/0xe0 ?
wait_for_completion_interruptible+0x1d7/0x320
? mutex_unlock+0x81/0xd0
amdgpu_vkms_crtc_atomic_disable
It's caused by a stuck in lock dependency in such scenario on
different CPUs.
CPU1 CPU2
drm_crtc_vblank_off hrtimer_interrupt
grab event_lock (irq disabled) __hrtimer_run_queues
grab vbl_lock/vblank_time_block
amdgpu_vkms_vblank_simulate
amdgpu_vkms_disable_vblank
drm_handle_vblank
hrtimer_cancel grab
dev->event_lock
So CPU1 stucks in hrtimer_cancel as timer callback is running
endless on current clock base, as that timer queue on CPU2 has no
chance to finish it because of failing to hold the lock. So NMI
watchdog will throw the errors after its threshold, and all later
CPUs are
impacted/blocked.
So use hrtimer_try_to_cancel to fix this, as disable_vblank callback
does not need to wait the handler to finish. And also it's not
necessary to check the return value of hrtimer_try_to_cancel,
because even if it's
-1 which means current timer callback is running, it will be
reprogrammed in hrtimer_start with calling enable_vblank to make it
works.
v2: only re-arm timer when vblank is enabled (Christian) and add a
Fixes tag as well
v3: drop warn printing (Christian)
Fixes: 84ec374bd580("drm/amdgpu: create amdgpu_vkms (v4)")
Cc:[email protected]
Suggested-by: Christian König<[email protected]>
Signed-off-by: Guchun Chen<[email protected]>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_vkms.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vkms.c
b/drivers/gpu/drm/amd/amdgpu/amdgpu_vkms.c
index 53ff91fc6cf6..b870c827cbaa 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vkms.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vkms.c
@@ -46,7 +46,10 @@ static enum hrtimer_restart
amdgpu_vkms_vblank_simulate(struct hrtimer *timer)
struct amdgpu_crtc *amdgpu_crtc = container_of(timer, struct
amdgpu_crtc, vblank_timer);
struct drm_crtc *crtc = &amdgpu_crtc->base;
struct amdgpu_vkms_output *output =
drm_crtc_to_amdgpu_vkms_output(crtc);
+ struct drm_vblank_crtc *vblank;
+ struct drm_device *dev;
u64 ret_overrun;
+ unsigned int pipe;
bool ret;
ret_overrun = hrtimer_forward_now(&amdgpu_crtc->vblank_timer,
@@ -54,9 +57,13 @@ static enum hrtimer_restart
amdgpu_vkms_vblank_simulate(struct hrtimer *timer)
if (ret_overrun != 1)
DRM_WARN("%s: vblank timer overrun\n", __func__);
+ dev = crtc->dev;
+ pipe = drm_crtc_index(crtc);
+ vblank = &dev->vblank[pipe];
ret = drm_crtc_handle_vblank(crtc);
- if (!ret)
- DRM_ERROR("amdgpu_vkms failure on handling vblank");
+ /* Don't queue timer again when vblank is disabled. */
+ if (!ret && !READ_ONCE(vblank->enabled))
+ return HRTIMER_NORESTART;
When drm_crtc_handle_vblank() returns false when vblank is disabled I
think we can simplify this to just removing the error.
Regards,
Christian.
Sorry, I didn't get you. What do you mean by "removing the error"?
We should just remove the "DRM_ERROR("amdgpu_vkms failure on handling
vblank");" message.
When the drm_crtc_handle_vblank() returns false it doesn't really indicate a
failure, it just indicates that the vblank is disabled and shouldn't be
re-armed.
Regards,
Christian.
drm_crtc_handle_vblank which is a wrapper of drm_handle_vblank, has two early test
calls to check if vblank is initialized. Though this will never happen in our
case, I still check the value of vblank->enabled when drm_crtc_handle_vblank
returns false, and when it's indeed disabled, return HRTIMER_NORESTART to not
re-arm timer, otherwise, returning HRTIMER_RESTART when it's going as expected.
Anything wrong or am I misunderstanding it?
The extra check for vblank enabled in the driver is just superfluous and
a little bit erroneous, see drm_handle_vblank():
/* Need timestamp lock to prevent concurrent execution with
* vblank enable/disable, as this would cause inconsistent
* or corrupted timestamps and vblank counts.
*/
spin_lock
<https://elixir.bootlin.com/linux/latest/C/ident/spin_lock>(&dev->vblank_time_lock
<https://elixir.bootlin.com/linux/latest/C/ident/vblank_time_lock>);
/* Vblank irq handling disabled. Nothing to do. */
if(!vblank
<https://elixir.bootlin.com/linux/latest/C/ident/vblank>->enabled
<https://elixir.bootlin.com/linux/latest/C/ident/enabled>){
spin_unlock
<https://elixir.bootlin.com/linux/latest/C/ident/spin_unlock>(&dev->vblank_time_lock
<https://elixir.bootlin.com/linux/latest/C/ident/vblank_time_lock>);
spin_unlock_irqrestore
<https://elixir.bootlin.com/linux/latest/C/ident/spin_unlock_irqrestore>(&dev->event_lock
<https://elixir.bootlin.com/linux/latest/C/ident/event_lock>,irqflags
<https://elixir.bootlin.com/linux/latest/C/ident/irqflags>);
returnfalse <https://elixir.bootlin.com/linux/latest/C/ident/false>;
}
This function already checks for us if vblank is enabled/disabled *and*
it also holds the correct locks to do so.
So we should *not* check that again in the driver, especially not
without holding the correct locks.
Regards,
Christian.
Regards,
Guchun
Regards,
Guchun
return HRTIMER_RESTART;
}
@@ -81,7 +88,7 @@ static void amdgpu_vkms_disable_vblank(struct
drm_crtc *crtc)
{
struct amdgpu_crtc *amdgpu_crtc = to_amdgpu_crtc(crtc);
- hrtimer_cancel(&amdgpu_crtc->vblank_timer);
+ hrtimer_try_to_cancel(&amdgpu_crtc->vblank_timer);
}
static bool amdgpu_vkms_get_vblank_timestamp(struct drm_crtc
*crtc,
