drm/sched: Check scheduler work queue before calling timeout handling

In the Linux kernel, the following vulnerability has been resolved: drm/sched: Check scheduler work queue before calling timeout handling During an IGT GPU reset test we see again oops despite of commit 0c8c901aaaebc9 (drm/sched: Check scheduler ready before calling timeout handling). It uses ready condition whether to call drm_sched_fault which unwind the TDR leads to GPU reset. However it looks the ready condition is overloaded with other meanings, for example, for the following stack is related GPU reset : 0 gfx_v9_0_cp_gfx_start 1 gfx_v9_0_cp_gfx_resume 2 gfx_v9_0_cp_resume 3 gfx_v9_0_hw_init 4 gfx_v9_0_resume 5 amdgpu_device_ip_resume_phase2 does the following: /* start the ring */ gfx_v9_0_cp_gfx_start(adev); ring->sched.ready = true; The same approach is for other ASICs as well : gfx_v8_0_cp_gfx_resume gfx_v10_0_kiq_resume, etc... As a result, our GPU reset test causes GPU fault which calls unconditionally gfx_v9_0_fault and then drm_sched_fault. However now it depends on whether the interrupt service routine drm_sched_fault is executed after gfx_v9_0_cp_gfx_start is completed which sets the ready field of the scheduler to true even for uninitialized schedulers and causes oops vs no fault or when ISR drm_sched_fault is completed prior gfx_v9_0_cp_gfx_start and NULL pointer dereference does not occur. Use the field timeout_wq to prevent oops for uninitialized schedulers. The field could be initialized by the work queue of resetting the domain. v1: Corrections to commit message (Luben)

The product uses or accesses a resource that has not been initialized.

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.