io_uring: drop mm and files after task_work_run

stable inclusion
from stable-5.10.9
commit f7f32822a44af3b09a1641d26803a8fea714ff88
bugzilla: 47457

--------------------------------

[ Upstream commit d434ab6d ]

__io_req_task_submit() run by task_work can set mm and files, but
io_sq_thread() in some cases, and because __io_sq_thread_acquire_mm()
and __io_sq_thread_acquire_files() do a simple current->mm/files check
it may end up submitting IO with mm/files of another task.

We also need to drop it after in the end to drop potentially grabbed
references to them.

Cc: stable@vger.kernel.org # 5.9+
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

fs/io_uring.c

@@ -6841,6 +6841,7 @@ static int io_sq_thread(void *data)
 
 		if (ret & SQT_SPIN) {
 			io_run_task_work();
+			io_sq_thread_drop_mm();
 			cond_resched();
 		} else if (ret == SQT_IDLE) {
 			if (kthread_should_park())
@@ -6855,6 +6856,7 @@ static int io_sq_thread(void *data)
 	}
 
 	io_run_task_work();
+	io_sq_thread_drop_mm();
 
 	if (cur_css)
 		io_sq_thread_unassociate_blkcg();