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drm/sched: Improve teardown documentation

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If jobs are still enqueued in struct drm_gpu_scheduler.pending_list
when drm_sched_fini() gets called, those jobs will be leaked since that
function stops both job-submission and (automatic) job-cleanup. It is,
thus, up to the driver to take care of preventing leaks.

The related function drm_sched_wqueue_stop() also prevents automatic job
cleanup.

Those pitfals are not reflected in the documentation, currently.

Explicitly inform about the leak problem in the docstring of
drm_sched_fini().

Additionally, detail the purpose of drm_sched_wqueue_{start,stop} and
hint at the consequences for automatic cleanup.

Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241105143137.71893-2-pstanner@redhat.com
This commit is contained in:
Philipp Stanner 2024-11-05 15:31:38 +01:00
parent 21c23e4b64
commit baf4afc583
1 changed files with 21 additions and 2 deletions
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23
drivers/gpu/drm/scheduler/sched_main.c
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@ -1350,6 +1350,19 @@ EXPORT_SYMBOL(drm_sched_init);
* @sched: scheduler instance
*
* Tears down and cleans up the scheduler.
*
* This stops submission of new jobs to the hardware through
* drm_sched_backend_ops.run_job(). Consequently, drm_sched_backend_ops.free_job()
* will not be called for all jobs still in drm_gpu_scheduler.pending_list.
* There is no solution for this currently. Thus, it is up to the driver to make
* sure that
* a) drm_sched_fini() is only called after for all submitted jobs
* drm_sched_backend_ops.free_job() has been called or that
* b) the jobs for which drm_sched_backend_ops.free_job() has not been called
* after drm_sched_fini() ran are freed manually.
*
* FIXME: Take care of the above problem and prevent this function from leaking
* the jobs in drm_gpu_scheduler.pending_list under any circumstances.
*/
void drm_sched_fini(struct drm_gpu_scheduler *sched)
{
@ -1445,8 +1458,10 @@ EXPORT_SYMBOL(drm_sched_wqueue_ready);
/**
* drm_sched_wqueue_stop - stop scheduler submission
*
* @sched: scheduler instance
*
* Stops the scheduler from pulling new jobs from entities. It also stops
* freeing jobs automatically through drm_sched_backend_ops.free_job().
*/
void drm_sched_wqueue_stop(struct drm_gpu_scheduler *sched)
{
@ -1458,8 +1473,12 @@ EXPORT_SYMBOL(drm_sched_wqueue_stop);
/**
* drm_sched_wqueue_start - start scheduler submission
*
* @sched: scheduler instance
*
* Restarts the scheduler after drm_sched_wqueue_stop() has stopped it.
*
* This function is not necessary for 'conventional' startup. The scheduler is
* fully operational after drm_sched_init() succeeded.
*/
void drm_sched_wqueue_start(struct drm_gpu_scheduler *sched)
{