io_uring: handle TIF_NOTIFY_RESUME when checking for task_work

If TIF_NOTIFY_RESUME is set, then we need to call resume_user_mode_work()
for PF_IO_WORKER threads. They never return to usermode, hence never get
a chance to process any items that are marked by this flag. Most notably
this includes the final put of files, but also any throttling markers set
by block cgroups.

Cc: stable@vger.kernel.org # 5.10+
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.h

@@ -3,6 +3,7 @@
 
 #include <linux/errno.h>
 #include <linux/lockdep.h>
+#include <linux/resume_user_mode.h>
 #include <linux/io_uring_types.h>
 #include <uapi/linux/eventpoll.h>
 #include "io-wq.h"
@@ -274,6 +275,13 @@ static inline int io_run_task_work(void)
 	 */
 	if (test_thread_flag(TIF_NOTIFY_SIGNAL))
 		clear_notify_signal();
+	/*
+	 * PF_IO_WORKER never returns to userspace, so check here if we have
+	 * notify work that needs processing.
+	 */
+	if (current->flags & PF_IO_WORKER &&
+	    test_thread_flag(TIF_NOTIFY_RESUME))
+		resume_user_mode_work(NULL);
 	if (task_work_pending(current)) {
 		__set_current_state(TASK_RUNNING);
 		task_work_run();