[PATCH 5/5] drm/amdkfd: svm deferred work pin mm

[Philip Yang <Philip.Yang@xxxxxxx>]

Make sure mm does not remove when prange deferred work insert mmu range
notifier, to avoid WARNING:

WARNING: CPU: 6 PID: 1787 at mm/mmu_notifier.c:932 __mmu_interval_notifier_insert+0xdd/0xf0
Workqueue: events svm_range_deferred_list_work [amdgpu]
RIP: 0010:__mmu_interval_notifier_insert+0xdd/0xf0
Call Trace:
  svm_range_deferred_list_work+0x156/0x320 [amdgpu]
  process_one_work+0x29f/0x5e0
  worker_thread+0x39/0x3e0

Signed-off-by: Philip Yang <Philip.Yang@xxxxxxx>
---
 drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
index 2083a10b35c2..fddf0a93d6f1 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
@@ -1992,6 +1992,13 @@ static void svm_range_deferred_list_work(struct work_struct *work)
 			 prange->start, prange->last, prange->work_item.op);
 
 		mm = prange->work_item.mm;
+		if (!mmget_not_zero(mm)) {
+			pr_debug("skip range %p as mm is gone\n", prange);
+			spin_lock(&svms->deferred_list_lock);
+			list_del_init(&prange->deferred_list);
+			continue;
+		}
+
 retry:
 		mmap_write_lock(mm);
 		mutex_lock(&svms->lock);
@@ -2032,6 +2039,7 @@ static void svm_range_deferred_list_work(struct work_struct *work)
 		svm_range_handle_list_op(svms, prange);
 		mutex_unlock(&svms->lock);
 		mmap_write_unlock(mm);
+		mmput(mm);
 
 		spin_lock(&svms->deferred_list_lock);
 	}
-- 
2.17.1