Re: [PATCH v4 2/6] drm/msm: Resume perfcntrs after hw_init

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] drm/msm: self-deadlock on perfcntr_lock in sel_worker() via msm_gpu_hw_init()
--

commit 5d6d3def9b6235a74e135666a5a4eea2adca8e09
Author: Rob Clark <robin.clark@oss.qualcomm.com>

drm/msm: Resume perfcntrs after hw_init

This commit moves msm_perfcntr_resume() from adreno_runtime_resume() and
adreno_recover() into msm_gpu_hw_init() so that performance counter sampling
resumes only after hardware initialization completes.

> diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
> index 0c2c356362518..b9a8c641001d0 100644
> --- a/drivers/gpu/drm/msm/msm_gpu.c
> +++ b/drivers/gpu/drm/msm/msm_gpu.c
> @@ -168,8 +168,10 @@ int msm_gpu_hw_init(struct msm_gpu *gpu)
>  
>  	disable_irq(gpu->irq);
>  	ret = gpu->funcs->hw_init(gpu);
> -	if (!ret)
> +	if (!ret) {
> +		msm_perfcntr_resume(gpu);
>  		gpu->needs_hw_init = false;
> +	}

[Severity: High]
Can calling msm_perfcntr_resume() inside msm_gpu_hw_init() deadlock on
gpu->perfcntr_lock when invoked from sel_worker()?

In drivers/gpu/drm/msm/msm_perfcntr.c, sel_worker() acquires both gpu->lock
and gpu->perfcntr_lock before calling msm_gpu_hw_init():

drivers/gpu/drm/msm/msm_perfcntr.c:sel_worker() {
	...
	scoped_guard (mutex, &gpu->lock) {
		guard(mutex)(&gpu->perfcntr_lock);

		if (stream == gpu->perfcntrs->stream) {
			msm_gpu_hw_init(gpu);
			gpu->funcs->perfcntr_configure(gpu, ring, stream);
		}
	}
}

And msm_perfcntr_resume() acquires gpu->perfcntr_lock again:

drivers/gpu/drm/msm/msm_perfcntr.c:msm_perfcntr_resume() {
	if (!gpu->perfcntrs)
		return 0;
	guard(mutex)(&gpu->perfcntr_lock);
	return msm_perfcntr_resume_locked(gpu->perfcntrs->stream);
}

If the GPU is runtime-PM active while gpu->needs_hw_init is still true (for
example, after adreno_runtime_resume() runs via pm_runtime_get_sync() in
adreno_get_param() or msm_context_set_sysprof() before any job submission
calls msm_gpu_hw_init()), opening a stream in msm_ioctl_perfcntr_config()
unconditionally calls msm_perfcntr_resume_locked(), which starts
stream->sample_timer and queues stream->sel_work.

When sel_worker() runs and calls msm_gpu_hw_init(gpu) with
gpu->needs_hw_init set, msm_gpu_hw_init() disables gpu->irq, runs
gpu->funcs->hw_init(gpu), and calls msm_perfcntr_resume(gpu), which attempts
to take gpu->perfcntr_lock while sel_worker() already holds it.

Even without the recursive lock acquisition, wouldn't calling
msm_perfcntr_resume() from the sel_worker() -> msm_gpu_hw_init() path also
redundantly re-queue stream->sel_work right before sel_worker() calls
gpu->funcs->perfcntr_configure()?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261103231850.17493-1-robin.clark@oss.qualcomm.com?part=2