task_work: add a scheduling point in task_work_run()

It seems commit 4a9d4b0 ("switch fput to task_work_add") re-
introduced the problem addressed in 944be0b ("close_files(): add
scheduling point")

If a server process with a lot of files (say 2 million tcp sockets) is
killed, we can spend a lot of time in task_work_run() and trigger a soft
lockup.

Signed-off-by: Eric Dumazet <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/task_work.c

@@ -75,6 +75,7 @@ void task_work_run(void)
 			p = q->next;
 			q->func(q);
 			q = p;
+			cond_resched();
 		}
 	}
 }