rust: block: fix GenDisk cleanup paths

GenDiskBuilder::build() still has fallible work after
__blk_mq_alloc_disk(), but its error path only recovers the
foreign queue data. That leaks the temporary gendisk and
request_queue until later teardown. If the caller moved the last
Arc<TagSet<T>> into build(), the leaked queue can retain blk-mq
state after the tag set is dropped.

Fix the pre-registration failure path by dropping the temporary
gendisk reference with put_disk() before recovering queue_data,
so disk_release() can tear down the owned queue.

Also pair GenDisk::drop() with put_disk() after del_gendisk().
Once a Rust GenDisk has been added with device_add_disk(),
del_gendisk() only unregisters it; the final gendisk reference
still has to be dropped to complete the release path.

Fixes: 3253aba ("rust: block: introduce `kernel::block::mq` module")
Cc: stable@kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Signed-off-by: Haoze Xie <royenheart@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Link: https://patch.msgid.link/b70aff9a920cc42110fe5cf454c3099561863519.1780063368.git.royenheart@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: royenheart

rust/kernel/block/mq/gen_disk.rs

@@ -150,6 +150,19 @@ impl GenDiskBuilder {
         // SAFETY: `gendisk` is a valid pointer as we initialized it above
         unsafe { (*gendisk).fops = &TABLE };
 
+        let cleanup_failure = ScopeGuard::new_with_data((gendisk, data), |(gendisk, data)| {
+            // SAFETY: `gendisk` came from `__blk_mq_alloc_disk()` above and
+            // has not been added to the VFS on this cleanup path.
+            unsafe { bindings::put_disk(gendisk) };
+            // SAFETY: `data` came from `into_foreign()` above and has not been
+            // converted back on this cleanup path.
+            drop(unsafe { T::QueueData::from_foreign(data) });
+        });
+
+        // The failure guard now owns both pieces of cleanup; the early guard
+        // must not run on this path anymore.
+        recover_data.dismiss();
+
         let mut writer = NullTerminatedFormatter::new(
             // SAFETY: `gendisk` points to a valid and initialized instance. We
             // have exclusive access, since the disk is not added to the VFS
@@ -172,7 +185,7 @@ impl GenDiskBuilder {
             },
         )?;
 
-        recover_data.dismiss();
+        cleanup_failure.dismiss();
 
         // INVARIANT: `gendisk` was initialized above.
         // INVARIANT: `gendisk` was added to the VFS via `device_add_disk` above.
@@ -215,6 +228,11 @@ impl<T: Operations> Drop for GenDisk<T> {
         // to the VFS.
         unsafe { bindings::del_gendisk(self.gendisk) };
 
+        // SAFETY: By type invariant, `self.gendisk` was added to the VFS, so
+        // `put_disk()` must follow `del_gendisk()` to drop the final gendisk
+        // reference and trigger the remaining release path.
+        unsafe { bindings::put_disk(self.gendisk) };
+
         // SAFETY: `queue.queuedata` was created by `GenDiskBuilder::build` with
         // a call to `ForeignOwnable::into_foreign` to create `queuedata`.
         // `ForeignOwnable::from_foreign` is only called here.