[RFC PATCH 2/2] drm/amdgpu: Use an rwsem for the notifier lock

[Thomas Hellström]

Use an rwsem as the notifier lock, and take it in read mode during
command submission.
This avoids the device-wide serialization of command submission in
the absence of userptr invalidations.

Cc: Christian König <christian.koenig at amd.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu.h              |  2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c |  2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c           | 12 ++++++++----
 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c       |  2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c           | 10 +++++-----
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c          |  2 +-
 6 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
index d356e329e6f8..04fec2299c02 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
@@ -1051,7 +1051,7 @@ struct amdgpu_device {
 	struct rw_semaphore reset_sem;
 	struct amdgpu_doorbell_index doorbell_index;
 
-	struct mutex			notifier_lock;
+	struct rw_semaphore		notifier_sem;
 
 	int asic_reset_res;
 	struct work_struct		xgmi_reset_work;
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
index 2d6b2d77b738..14be51692539 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
@@ -2049,7 +2049,7 @@ static int update_invalid_user_pages(struct amdkfd_process_info *process_info,
 
 		/*
 		 * FIXME: Cannot ignore the return code, must hold
-		 * notifier_lock
+		 * notifier_sem in read mode.
 		 */
 		amdgpu_ttm_tt_get_user_pages_done(bo->tbo.ttm);
 
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
index 0311d799a010..26f447c49bdd 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
@@ -1224,11 +1224,13 @@ static int amdgpu_cs_submit(struct amdgpu_cs_parser *p,
 
 	drm_sched_job_arm(&job->base);
 
-	/* No memory allocation is allowed while holding the notifier lock.
+	/* No memory allocation is allowed while holding the notifier sem.
 	 * The lock is held until amdgpu_cs_submit is finished and fence is
 	 * added to BOs.
 	 */
-	mutex_lock(&p->adev->notifier_lock);
+	r = down_read_interruptible(&p->adev->notifier_sem);
+	if (r)
+		goto error_notifier;
 
 	/* If userptr are invalidated after amdgpu_cs_parser_bos(), return
 	 * -EAGAIN, drmIoctl in libdrm will restart the amdgpu_cs_ioctl.
@@ -1288,13 +1290,15 @@ static int amdgpu_cs_submit(struct amdgpu_cs_parser *p,
 	}
 
 	ttm_eu_fence_buffer_objects(&p->ticket, &p->validated, p->fence);
-	mutex_unlock(&p->adev->notifier_lock);
+	up_read(&p->adev->notifier_sem);
 
 	return 0;
 
 error_abort:
+	up_read(&p->adev->notifier_sem);
+
+error_notifier:
 	drm_sched_job_cleanup(&job->base);
-	mutex_unlock(&p->adev->notifier_lock);
 
 error_unlock:
 	amdgpu_job_free(job);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 48089dc0180b..aa27b462152d 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -3476,7 +3476,7 @@ int amdgpu_device_init(struct amdgpu_device *adev,
 	atomic_set(&adev->in_gpu_reset, 0);
 	init_rwsem(&adev->reset_sem);
 	mutex_init(&adev->psp.mutex);
-	mutex_init(&adev->notifier_lock);
+	init_rwsem(&adev->notifier_sem);
 
 	r = amdgpu_device_init_apu_flags(adev);
 	if (r)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
index d3d340a6129c..e0b1b6e11bf5 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
@@ -71,11 +71,11 @@ static bool amdgpu_mn_invalidate_gfx(struct mmu_interval_notifier *mni,
 	if (!mmu_notifier_range_blockable(range))
 		return false;
 
-	mutex_lock(&adev->notifier_lock);
+	down_write(&adev->notifier_sem);
 
 	mmu_interval_set_seq(mni, cur_seq);
 
-	mutex_unlock(&adev->notifier_lock);
+	up_write(&adev->notifier_sem);
 
 	r = dma_resv_wait_timeout(bo->tbo.base.resv, true, false,
 				  MAX_SCHEDULE_TIMEOUT);
@@ -108,12 +108,12 @@ static bool amdgpu_mn_invalidate_hsa(struct mmu_interval_notifier *mni,
 	if (!mmu_notifier_range_blockable(range))
 		return false;
 
-	mutex_lock(&adev->notifier_lock);
+	down_write(&adev->notifier_sem);
 
 	mmu_interval_set_seq(mni, cur_seq);
 
 	amdgpu_amdkfd_evict_userptr(bo->kfd_bo, bo->notifier.mm);
-	mutex_unlock(&adev->notifier_lock);
+	up_write(&adev->notifier_sem);
 
 	return true;
 }
@@ -215,7 +215,7 @@ int amdgpu_hmm_range_get_pages(struct mmu_interval_notifier *notifier,
 	/*
 	 * Due to default_flags, all pages are HMM_PFN_VALID or
 	 * hmm_range_fault() fails. FIXME: The pages cannot be touched outside
-	 * the notifier_lock, and mmu_interval_read_retry() must be done first.
+	 * the notifier_sem, and mmu_interval_read_retry() must be done first.
 	 */
 	for (i = 0; pages && i < npages; i++)
 		pages[i] = hmm_pfn_to_page(pfns[i]);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 0cf94421665f..b2af53a05fb5 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -723,7 +723,7 @@ bool amdgpu_ttm_tt_get_user_pages_done(struct ttm_tt *ttm)
 
 	if (gtt->range) {
 		/*
-		 * FIXME: Must always hold notifier_lock for this, and must
+		 * FIXME: Must always hold notifier_sem for this, and must
 		 * not ignore the return code.
 		 */
 		r = amdgpu_hmm_range_get_pages_done(gtt->range);
-- 
2.31.1