drm/i915: use xa_lock/unlock for fpriv->vm_xa lookups

We don't need the absolute speed of rcu for this. And
i915_address_space in general dont need rcu protection anywhere else,
after we've made gem contexts and engines a lot more immutable.

Note that this semantically reverts

commit aabbe344dc3ca5f7d8263a02608ba6179e8a4499
Author: Chris Wilson <[email protected]>
Date:   Fri Aug 30 19:03:25 2019 +0100

    drm/i915: Use RCU for unlocked vm_idr lookup

except we have the conversion from idr to xarray in between.

v2: kref_get_unless_zero is no longer required (Maarten)

Reviewed-by: Maarten Lankhorst <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Cc: Jon Bloomfield <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Joonas Lahtinen <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: "Thomas Hellström" <[email protected]>
Cc: Matthew Auld <[email protected]>
Cc: Lionel Landwerlin <[email protected]>
Cc: Dave Airlie <[email protected]>
Cc: Jason Ekstrand <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

1 files changed, 4 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 0558921663d9..94175a49c151 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1888,11 +1888,11 @@ i915_gem_vm_lookup(struct drm_i915_file_private *file_priv, u32 id)
 {
 	struct i915_address_space *vm;
 
-	rcu_read_lock();
+	xa_lock(&file_priv->vm_xa);
 	vm = xa_load(&file_priv->vm_xa, id);
-	if (vm && !kref_get_unless_zero(&vm->ref))
-		vm = NULL;
-	rcu_read_unlock();
+	if (vm)
+		kref_get(&vm->ref);
+	xa_unlock(&file_priv->vm_xa);
 
 	return vm;
 }