Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
Pre-existing issues: - [High] vlv_atomic_update_fifo() takes a sleepable spinlock (uncore->lock) inside a hardware-interrupt-disabled critical section, leading to a 'sleeping function called from invalid context' BUG on PREEMPT_RT. -- commit 5a85aa91d02b113ff09052cce4d68e8a6b54e2ce Author: Maarten Lankhorst <[email protected]> drm/i915/display: Make set_pipeconf use the fw variants This commit changes i9xx_set_pipeconf() and ilk_set_pipeconf() to use the _fw variants of register read/write functions. This prevents sleepable locks from being taken inside the interrupt-disabled critical section, which was causing a BUG on PREEMPT_RT. > diff --git a/drivers/gpu/drm/i915/display/intel_display.c > b/drivers/gpu/drm/i915/display/intel_display.c > index f5dac380aa7ff..deb93d26e0e94 100644 > --- a/drivers/gpu/drm/i915/display/intel_display.c > +++ b/drivers/gpu/drm/i915/display/intel_display.c > @@ -3030,8 +3030,9 @@ void i9xx_set_pipeconf(const struct intel_crtc_state > *crtc_state) > > val |= TRANSCONF_FRAME_START_DELAY(crtc_state->framestart_delay - 1); > > - intel_de_write(display, TRANSCONF(display, cpu_transcoder), val); > - intel_de_posting_read(display, TRANSCONF(display, cpu_transcoder)); > + intel_de_write_fw(display, TRANSCONF(display, cpu_transcoder), val); > + /* posting read */ > + intel_de_read_fw(display, TRANSCONF(display, cpu_transcoder)); > } [Severity: High] This isn't a bug introduced by this patch, but does the explicit acquisition of a sleepable spinlock inside an interrupt-disabled critical section in vlv_atomic_update_fifo() violate PREEMPT_RT locking rules? drivers/gpu/drm/i915/display/i9xx_wm.c:vlv_atomic_update_fifo() { ... /* * intel_pipe_update_start() has already disabled interrupts * for us, so a plain spin_lock() is sufficient here. */ spin_lock(&uncore->lock); ... } Taking a standard spinlock (which acts as a sleeping rt_mutex on PREEMPT_RT) after local interrupts have been disabled causes a kernel BUG splat 'sleeping function called from invalid context'. The vblank evasion critical section initiated by intel_pipe_update_start() disables local interrupts. Inside this critical section, commit_pipe_pre_planes() calls intel_atomic_update_watermarks(), which on VLV/CHV maps to vlv_atomic_update_fifo(). This function explicitly acquires spin_lock(&uncore->lock). Since this patch fixes the same locking violation in i9xx_set_pipeconf() and ilk_set_pipeconf() by using the _fw variants, is it possible this instance in the exact same critical section was missed? [ ... ] -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=4
