drm/amdkfd: process exit and retry fault race

kfd_process_wq_release drain retry fault to ensure no retry fault comes
after removing kfd process from the hash table, otherwise svm page fault
handler will fail to recover the fault and dump GPU vm fault log.

Refactor deferred list work to get_task_mm and take mmap write lock
to handle all ranges, and avoid mm is gone while inserting mmu notifier.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_svm.c

@@ -1990,43 +1990,42 @@ static void svm_range_deferred_list_work(struct work_struct *work)
 	struct svm_range_list *svms;
 	struct svm_range *prange;
 	struct mm_struct *mm;
+	struct kfd_process *p;
 
 	svms = container_of(work, struct svm_range_list, deferred_list_work);
 	pr_debug("enter svms 0x%p\n", svms);
 
+	p = container_of(svms, struct kfd_process, svms);
+	/* Avoid mm is gone when inserting mmu notifier */
+	mm = get_task_mm(p->lead_thread);
+	if (!mm) {
+		pr_debug("svms 0x%p process mm gone\n", svms);
+		return;
+	}
+retry:
+	mmap_write_lock(mm);
+
+	/* Checking for the need to drain retry faults must be inside
+	 * mmap write lock to serialize with munmap notifiers.
+	 */
+	if (unlikely(READ_ONCE(svms->drain_pagefaults))) {
+		WRITE_ONCE(svms->drain_pagefaults, false);
+		mmap_write_unlock(mm);
+		svm_range_drain_retry_fault(svms);
+		goto retry;
+	}
+
 	spin_lock(&svms->deferred_list_lock);
 	while (!list_empty(&svms->deferred_range_list)) {
 		prange = list_first_entry(&svms->deferred_range_list,
 					  struct svm_range, deferred_list);
+		list_del_init(&prange->deferred_list);
 		spin_unlock(&svms->deferred_list_lock);
+
 		pr_debug("prange 0x%p [0x%lx 0x%lx] op %d\n", prange,
 			 prange->start, prange->last, prange->work_item.op);
 
-		mm = prange->work_item.mm;
-retry:
-		mmap_write_lock(mm);
 		mutex_lock(&svms->lock);
-
-		/* Checking for the need to drain retry faults must be in
-		 * mmap write lock to serialize with munmap notifiers.
-		 *
-		 * Remove from deferred_list must be inside mmap write lock,
-		 * otherwise, svm_range_list_lock_and_flush_work may hold mmap
-		 * write lock, and continue because deferred_list is empty, then
-		 * deferred_list handle is blocked by mmap write lock.
-		 */
-		spin_lock(&svms->deferred_list_lock);
-		if (unlikely(svms->drain_pagefaults)) {
-			svms->drain_pagefaults = false;
-			spin_unlock(&svms->deferred_list_lock);
-			mutex_unlock(&svms->lock);
-			mmap_write_unlock(mm);
-			svm_range_drain_retry_fault(svms);
-			goto retry;
-		}
-		list_del_init(&prange->deferred_list);
-		spin_unlock(&svms->deferred_list_lock);
-
 		mutex_lock(&prange->migrate_mutex);
 		while (!list_empty(&prange->child_list)) {
 			struct svm_range *pchild;
@@ -2042,12 +2041,13 @@ 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);
 
 		spin_lock(&svms->deferred_list_lock);
 	}
 	spin_unlock(&svms->deferred_list_lock);
 
+	mmap_write_unlock(mm);
+	mmput(mm);
 	pr_debug("exit svms 0x%p\n", svms);
 }
 
@@ -2600,7 +2600,7 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 	p = kfd_lookup_process_by_pasid(pasid);
 	if (!p) {
 		pr_debug("kfd process not founded pasid 0x%x\n", pasid);
-		return -ESRCH;
+		return 0;
 	}
 	if (!p->xnack_enabled) {
 		pr_debug("XNACK not enabled for pasid 0x%x\n", pasid);
@@ -2611,10 +2611,12 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
 
 	pr_debug("restoring svms 0x%p fault address 0x%llx\n", svms, addr);
 
+	/* p->lead_thread is available as kfd_process_wq_release flush the work
+	 * before releasing task ref.
+	 */
 	mm = get_task_mm(p->lead_thread);
 	if (!mm) {
 		pr_debug("svms 0x%p failed to get mm\n", svms);
-		r = -ESRCH;
 		goto out;
 	}
 
@@ -2741,6 +2743,13 @@ void svm_range_list_fini(struct kfd_process *p)
 	/* Ensure list work is finished before process is destroyed */
 	flush_work(&p->svms.deferred_list_work);
 
+	/*
+	 * Ensure no retry fault comes in afterwards, as page fault handler will
+	 * not find kfd process and take mm lock to recover fault.
+	 */
+	svm_range_drain_retry_fault(&p->svms);
+
+
 	list_for_each_entry_safe(prange, next, &p->svms.list, list) {
 		svm_range_unlink(prange);
 		svm_range_remove_notifier(prange);