io_uring: cancel by ->task not pid

For an exiting process it tries to cancel all its inflight requests. Use
req->task to match such instead of work.pid. We always have req->task
set, and it will be valid because we're matching only current exiting
task.

Also, remove work.pid and everything related, it's useless now.
Reported-by: NEric W. Biederman <ebiederm@xmission.com>
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

fs/io-wq.h

@@ -90,7 +90,6 @@ struct io_wq_work {
 	const struct cred *creds;
 	struct fs_struct *fs;
 	unsigned flags;
-	pid_t task_pid;
 };
 
 static inline struct io_wq_work *wq_next_work(struct io_wq_work *work)

fs/io_uring.c

@@ -1063,8 +1063,6 @@ static inline void io_req_work_grab_env(struct io_kiocb *req,
 		}
 		spin_unlock(&current->fs->lock);
 	}
-	if (!req->work.task_pid)
-		req->work.task_pid = task_pid_vnr(current);
 }
 
 static inline void io_req_work_drop_env(struct io_kiocb *req)
@@ -7451,11 +7449,12 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx,
 	}
 }
 
-static bool io_cancel_pid_cb(struct io_wq_work *work, void *data)
+static bool io_cancel_task_cb(struct io_wq_work *work, void *data)
 {
-	pid_t pid = (pid_t) (unsigned long) data;
+	struct io_kiocb *req = container_of(work, struct io_kiocb, work);
+	struct task_struct *task = data;
 
-	return work->task_pid == pid;
+	return req->task == task;
 }
 
 static int io_uring_flush(struct file *file, void *data)
@@ -7467,11 +7466,8 @@ static int io_uring_flush(struct file *file, void *data)
 	/*
 	 * If the task is going away, cancel work it may have pending
 	 */
-	if (fatal_signal_pending(current) || (current->flags & PF_EXITING)) {
-		void *data = (void *) (unsigned long)task_pid_vnr(current);
-
-		io_wq_cancel_cb(ctx->io_wq, io_cancel_pid_cb, data, true);
-	}
+	if (fatal_signal_pending(current) || (current->flags & PF_EXITING))
+		io_wq_cancel_cb(ctx->io_wq, io_cancel_task_cb, current, true);
 
 	return 0;
 }