drm/xe/devcoredump: Print errno if VM snapshot was not captured

My testing machine has only 8GB of RAM and while running piglit tests
I can reach the OOM cache in xe_vm_snapshot_capture() snap allocaiton
sometimes.

So to differentiate the OOM from race between capture and UMDs
unbinbind VMs here I'm adding a '[0].error: -12' to devcoredump.

v2:
- fix returned errno values

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240307135229.41973-2-jose.souza@intel.com

drivers/gpu/drm/xe/xe_devcoredump.c

@@ -120,10 +120,8 @@ static ssize_t xe_devcoredump_read(char *buffer, loff_t offset,
 		if (coredump->snapshot.hwe[i])
 			xe_hw_engine_snapshot_print(coredump->snapshot.hwe[i],
 						    &p);
-	if (coredump->snapshot.vm) {
-		drm_printf(&p, "\n**** VM state ****\n");
-		xe_vm_snapshot_print(coredump->snapshot.vm, &p);
-	}
+	drm_printf(&p, "\n**** VM state ****\n");
+	xe_vm_snapshot_print(coredump->snapshot.vm, &p);
 
 	return count - iter.remain;
 }

drivers/gpu/drm/xe/xe_vm.c

@@ -3359,8 +3359,10 @@ struct xe_vm_snapshot *xe_vm_snapshot_capture(struct xe_vm *vm)
 
 	if (num_snaps)
 		snap = kvzalloc(offsetof(struct xe_vm_snapshot, snap[num_snaps]), GFP_NOWAIT);
-	if (!snap)
+	if (!snap) {
+		snap = num_snaps ? ERR_PTR(-ENOMEM) : ERR_PTR(-ENODEV);
 		goto out_unlock;
+	}
 
 	snap->num_snaps = num_snaps;
 	i = 0;
@@ -3400,7 +3402,7 @@ struct xe_vm_snapshot *xe_vm_snapshot_capture(struct xe_vm *vm)
 
 void xe_vm_snapshot_capture_delayed(struct xe_vm_snapshot *snap)
 {
-	if (!snap)
+	if (IS_ERR(snap))
 		return;
 
 	for (int i = 0; i < snap->num_snaps; i++) {
@@ -3457,6 +3459,11 @@ void xe_vm_snapshot_print(struct xe_vm_snapshot *snap, struct drm_printer *p)
 {
 	unsigned long i, j;
 
+	if (IS_ERR(snap)) {
+		drm_printf(p, "[0].error: %li\n", PTR_ERR(snap));
+		return;
+	}
+
 	for (i = 0; i < snap->num_snaps; i++) {
 		drm_printf(p, "[%llx].length: 0x%lx\n", snap->snap[i].ofs, snap->snap[i].len);
 
@@ -3483,7 +3490,7 @@ void xe_vm_snapshot_free(struct xe_vm_snapshot *snap)
 {
 	unsigned long i;
 
-	if (!snap)
+	if (IS_ERR(snap))
 		return;
 
 	for (i = 0; i < snap->num_snaps; i++) {