Re: [PATCH v6 19/24] drm/xe: Add ULLS migration job support to migration layer

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Holding job_mutex while waiting on a dma_fence in xe_migrate_ulls_exit violates the dma_fence contract and risks deadlocks during GPU reset.
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commit bbc9d2795fb53c65f8a7edb5c701c0f994595d7a
Author: Matthew Brost <matthew.brost@intel.com>

drm/xe: Add ULLS migration job support to migration layer

This commit adds a function to enter ULLS mode for migration jobs and a
delayed worker to exit it for power savings. It sets flags on migration
jobs so submission backends can submit in ULLS mode, which is only
supported on DGFX and USM platforms.

Link: https://patch.msgid.link/20260228013501.106680-21-matthew.brost@intel.com

> diff --git a/drivers/gpu/drm/xe/xe_migrate.c b/drivers/gpu/drm/xe/xe_migrate.c
> index 471ae5741836e..3e59aeeca614d 100644
> --- a/drivers/gpu/drm/xe/xe_migrate.c
> +++ b/drivers/gpu/drm/xe/xe_migrate.c

[ ... ]

> @@ -448,6 +468,161 @@ static int xe_migrate_lock_prepare_vm(struct xe_tile *tile, struct xe_migrate *m
[ ... ]
> +static void xe_migrate_ulls_exit(struct work_struct *work)
> +{
[ ... ]
> +	mutex_lock(&m->job_mutex);
> +
> +	if (!xe_exec_queue_is_idle(m->q, 1))
> +		goto unlock_exit;
> +
> +	xe_sched_job_get(job);
> +	fence = __xe_migrate_job_push(m, job, ULLS_EXIT);
> +
> +	/* Serialize the PM put against the ring being taken off the hardware */
> +	dma_fence_wait(fence, false);

[Severity: High]
Can this lead to a deadlock during GPU reset?

In xe_migrate_ulls_exit(), the delayed worker acquires m->job_mutex, pushes
the ULLS_EXIT job, and blocks on its completion fence via dma_fence_wait()
before releasing the mutex.

Since m->job_mutex is explicitly tainted with fs_reclaim during
initialization, marking it as used in memory reclaim paths, blocking on a
dma_fence while holding this lock violates dma_fence locking rules. Fence
signaling can depend on memory allocations, creating a circular dependency
(job_mutex -> dma_fence -> fs_reclaim -> job_mutex).

If the GPU hangs while processing the ULLS_EXIT job, the thread blocks
indefinitely. Will the DRM scheduler's GPU reset recovery path permanently
deadlock here if it needs to evict memory using xe_migrate_copy() or
xe_migrate_clear(), which also attempt to acquire m->job_mutex?

> +	dma_fence_put(fence);
> +
> +	m->ulls.enabled = false;
> +unlock_exit:
> +	if (job)
> +		xe_sched_job_put(job);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260904211613.3934307-1-matthew.brost@intel.com?part=19