[PATCH] drm/amdkfd: Fix the deadlock in svm_range_restore_work

[Emily Deng]

It will hit deadlock in svm_range_restore_work ramdonly.
Detail as below:
1.svm_range_restore_work
	->svm_range_list_lock_and_flush_work
	->mmap_write_lock
2.svm_range_restore_work
	->svm_range_validate_and_map
	->amdgpu_vm_update_range
	->amdgpu_vm_ptes_update
	->amdgpu_vm_pt_alloc
	->svm_range_evict_svm_bo_worker
	->mmap_read_lock(deadlock here, because already get mmap_write_lock)

How to fix?
Downgrade the write lock to read lock.

Signed-off-by: Emily Deng <Emily.Deng at amd.com>
---
 drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
index bd3e20d981e0..c907e2de3dde 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
@@ -1841,6 +1841,7 @@ static void svm_range_restore_work(struct work_struct *work)
 	mutex_lock(&process_info->lock);
 	svm_range_list_lock_and_flush_work(svms, mm);
 	mutex_lock(&svms->lock);
+	mmap_write_downgrade(mm);
 
 	evicted_ranges = atomic_read(&svms->evicted_ranges);
 
@@ -1890,7 +1891,7 @@ static void svm_range_restore_work(struct work_struct *work)
 
 out_reschedule:
 	mutex_unlock(&svms->lock);
-	mmap_write_unlock(mm);
+	mmap_read_unlock(mm);
 	mutex_unlock(&process_info->lock);
 
 	/* If validation failed, reschedule another attempt */
-- 
2.34.1