[Intel-xe] [PATCH 1/5] drm/xe: Kill small race with userptr invalidation

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Theoretically, we can hit a small race where we hit an invalidation
after taking the lock in read-mode. In this case, take it in write
mode instead.

I don't think this is really an issue, but more of a robustness thing.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
---
 drivers/gpu/drm/xe/xe_exec.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_exec.c b/drivers/gpu/drm/xe/xe_exec.c
index e44076ee2e11..187108c4be6d 100644
--- a/drivers/gpu/drm/xe/xe_exec.c
+++ b/drivers/gpu/drm/xe/xe_exec.c
@@ -256,6 +256,13 @@ int xe_exec_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 		/* We don't allow execs while the VM is in error state */
 		err = down_read_interruptible(&vm->lock);
 		write_locked = false;
+
+		/* Userptr invalidation while we were still acquiring lock? */
+		if (!err && !xe_vm_no_dma_fences(vm) && xe_vm_userptr_check_repin(vm)) {
+			up_read(&vm->lock);
+			err = down_write_killable(&vm->lock);
+			write_locked = true;
+		}
 	}
 	if (err)
 		goto err_syncs;
-- 
2.34.1