fix(core): drop PendingSubmission's guards in reverse acquisition order (#9960)

Co-authored-by: Erich Gubler <erichdongubler@gmail.com>

Author: AdrianEddy

CHANGELOG.md

@@ -80,6 +80,7 @@ Bottom level categories:
 
 - Zero-initialize padding (if any) at the end of a buffer allocation. This was application-visible in rare cases on Vulkan when a shader read beyond the valid range of a vertex buffer. By @andyleiserson in [#9791](https://github.com/gfx-rs/wgpu/pull/9791).
 - Fix required immediate slots calculation and remove `naga::valid::FunctionInfo::immediate_slots_used`. By @beicause in [#9725](https://github.com/gfx-rs/wgpu/pull/9725).
+- Fix `PendingSubmission` releasing its lock guards out of stacking order, which tripped `--cfg wgpu_validate_locks` on any submission. By @AdrianEddy in [#9960](https://github.com/gfx-rs/wgpu/pull/9960).
 
 #### naga
 

wgpu-core/src/device/queue.rs

@@ -638,8 +638,10 @@ impl WebGpuError for QueueSubmitError {
 /// [`submit`]: `PendingSubmission::submit`
 pub(crate) struct PendingSubmission<'a> {
     queue: &'a Queue,
-    snatch_guard: SnatchGuard<'a>,
+    // NOTE: Guards must be declared in reverse of acquisition order, so  `wgpu_validate_locks`
+    // succeeds.
     command_index_guard: RwLockWriteGuard<'a, CommandIndices>,
+    snatch_guard: SnatchGuard<'a>,
     // Command buffers to be executed, along with trackers for the resources they use.
     pub executions: Vec<EncoderInFlight>,
     // Surface textures referenced by command buffers in this submission. These need to be