Am 12.07.23 um 03:34 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)
v4: drop superfluous check of blank->enabled in timer function, as it's guaranteed in drm_handle_vblank (Christian)
Fixes: 84ec374bd580("drm/amdgpu: create amdgpu_vkms (v4)") Cc: stable@vger.kernel.org Suggested-by: Christian König christian.koenig@amd.com Signed-off-by: Guchun Chen guchun.chen@amd.com
Reviewed-by: Christian König christian.koenig@amd.com
drivers/gpu/drm/amd/amdgpu/amdgpu_vkms.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vkms.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vkms.c index 53ff91fc6cf6..d0748bcfad16 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vkms.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vkms.c @@ -55,8 +55,9 @@ static enum hrtimer_restart amdgpu_vkms_vblank_simulate(struct hrtimer *timer) DRM_WARN("%s: vblank timer overrun\n", __func__); ret = drm_crtc_handle_vblank(crtc);
- /* Don't queue timer again when vblank is disabled. */ if (!ret)
DRM_ERROR("amdgpu_vkms failure on handling vblank");
return HRTIMER_NORESTART;return HRTIMER_RESTART; } @@ -81,7 +82,7 @@ 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,