[Intel-xe] [RFC] drm/xe: Handle -EDEADLK case in preempt worker

[Niranjana Vishwanathapura]

With multiple active VMs, under memory pressure, it is possible that
ttm_bo_validate() run into -EDEADLK in ttm_mem_evict_wait_busy() and
return -ENOMEM.

Until ttm properly handles locking in such scenarios, best thing the
driver can do is unwind the lock and retry.

Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura at intel.com>
---
 drivers/gpu/drm/xe/xe_vm.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index 91576cec000d..df1214f00a06 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -10,6 +10,7 @@
 #include <drm/ttm/ttm_execbuf_util.h>
 #include <drm/ttm/ttm_tt.h>
 #include <drm/xe_drm.h>
+#include <linux/delay.h>
 #include <linux/kthread.h>
 #include <linux/mm.h>
 #include <linux/swap.h>
@@ -508,11 +509,15 @@ void xe_vm_unlock_dma_resv(struct xe_vm *vm,
 		kvfree(tv);
 }
 
+#define XE_VM_REBIND_RETRY_TIMEOUT_MS 1000
+
 static void preempt_rebind_work_func(struct work_struct *w)
 {
 	struct xe_vm *vm = container_of(w, struct xe_vm, preempt.rebind_work);
 	struct xe_vma *vma;
 	struct ttm_validate_buffer tv_onstack[XE_ONSTACK_TV];
+	const ktime_t retry_end = ktime_add_ms(ktime_get(),
+					       XE_VM_REBIND_RETRY_TIMEOUT_MS);
 	struct ttm_validate_buffer *tv;
 	struct ww_acquire_ctx ww;
 	struct list_head objs;
@@ -637,6 +642,19 @@ static void preempt_rebind_work_func(struct work_struct *w)
 		trace_xe_vm_rebind_worker_retry(vm);
 		goto retry;
 	}
+
+	/*
+	 * With multiple active VMs, under memory pressure, it is possible that
+	 * ttm_bo_validate() run into -EDEADLK and in such case returns -ENOMEM.
+	 * Until ttm properly handles locking in such scenarios, best thing the
+	 * driver can do is retry with a timeout. Killing the VM or putting it
+	 * in error state after timeout or other error scenarios is still TBD.
+	 */
+	if ((err == -ENOMEM) && ktime_before(ktime_get(), retry_end)) {
+		msleep(20);
+		trace_xe_vm_rebind_worker_retry(vm);
+		goto retry;
+	}
 	up_write(&vm->lock);
 
 	free_preempt_fences(&preempt_fences);
-- 
2.21.0.rc0.32.g243a4c7e27