[PATCH v5 15/30] drm/xe/vf: Avoid indefinite blocking in preempt rebind worker for VFs supporting migration

[Matthew Brost <matthew.brost@intel.com>]

Blocking in work queues on a hardware action that may never occur —
especially when it depends on a software fixup also scheduled on the
a work queue — is a recipe for deadlock. This situation arises with
the preempt rebind worker and VF post-migration recovery. To prevent
potential deadlocks, avoid indefinite blocking in the preempt rebind
worker for VFs that support migration.

v4:
 - Use dma_fence_wait_timeout (CI)

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Tomasz Lis <tomasz.lis@intel.com>
---
 drivers/gpu/drm/xe/xe_vm.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index 4e914928e0a9..faca626702b8 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -35,6 +35,7 @@
 #include "xe_pt.h"
 #include "xe_pxp.h"
 #include "xe_res_cursor.h"
+#include "xe_sriov_vf.h"
 #include "xe_svm.h"
 #include "xe_sync.h"
 #include "xe_tile.h"
@@ -111,12 +112,22 @@ static int alloc_preempt_fences(struct xe_vm *vm, struct list_head *list,
 static int wait_for_existing_preempt_fences(struct xe_vm *vm)
 {
 	struct xe_exec_queue *q;
+	bool vf_migration = IS_SRIOV_VF(vm->xe) &&
+		xe_sriov_vf_migration_supported(vm->xe);
+	signed long wait_time = vf_migration ? HZ / 5 : MAX_SCHEDULE_TIMEOUT;
 
 	xe_vm_assert_held(vm);
 
 	list_for_each_entry(q, &vm->preempt.exec_queues, lr.link) {
 		if (q->lr.pfence) {
-			long timeout = dma_fence_wait(q->lr.pfence, false);
+			long timeout;
+
+			timeout = dma_fence_wait_timeout(q->lr.pfence, false,
+							 wait_time);
+			if (!timeout) {
+				xe_assert(vm->xe, vf_migration);
+				return -EAGAIN;
+			}
 
 			/* Only -ETIME on fence indicates VM needs to be killed */
 			if (timeout < 0 || q->lr.pfence->error == -ETIME)
@@ -541,6 +552,19 @@ static void preempt_rebind_work_func(struct work_struct *w)
 out_unlock_outer:
 	if (err == -EAGAIN) {
 		trace_xe_vm_rebind_worker_retry(vm);
+
+		/*
+		 * We can't block in workers on a VF which supports migration
+		 * given this can block the VF post-migration workers from
+		 * getting scheduled.
+		 */
+		if (IS_SRIOV_VF(vm->xe) &&
+		    xe_sriov_vf_migration_supported(vm->xe)) {
+			up_write(&vm->lock);
+			xe_vm_queue_rebind_worker(vm);
+			return;
+		}
+
 		goto retry;
 	}
 
-- 
2.34.1