io-wq: add support for uncancellable work

Not all work can be cancelled, some of it we may need to guarantee
that it runs to completion. Allow the caller to set IO_WQ_WORK_NO_CANCEL
on work that must not be cancelled. Note that the caller work function
must also check for IO_WQ_WORK_NO_CANCEL on work that is marked
IO_WQ_WORK_CANCEL.
Signed-off-by: NJens Axboe <axboe@kernel.dk>

fs/io-wq.c

@@ -456,6 +456,10 @@ static void io_worker_handle_work(struct io_worker *worker)
 		}
 		if (!worker->creds)
 			worker->creds = override_creds(wq->creds);
+		/*
+		 * OK to set IO_WQ_WORK_CANCEL even for uncancellable work,
+		 * the worker function will do the right thing.
+		 */
 		if (test_bit(IO_WQ_BIT_CANCEL, &wq->state))
 			work->flags |= IO_WQ_WORK_CANCEL;
 		if (worker->mm)
@@ -828,6 +832,7 @@ static bool io_work_cancel(struct io_worker *worker, void *cancel_data)
 	 */
 	spin_lock_irqsave(&worker->lock, flags);
 	if (worker->cur_work &&
+	    !(worker->cur_work->flags & IO_WQ_WORK_NO_CANCEL) &&
 	    data->cancel(worker->cur_work, data->caller_data)) {
 		send_sig(SIGINT, worker->task, 1);
 		ret = true;
@@ -902,7 +907,8 @@ static bool io_wq_worker_cancel(struct io_worker *worker, void *data)
 		return false;
 
 	spin_lock_irqsave(&worker->lock, flags);
-	if (worker->cur_work == work) {
+	if (worker->cur_work == work &&
+	    !(worker->cur_work->flags & IO_WQ_WORK_NO_CANCEL)) {
 		send_sig(SIGINT, worker->task, 1);
 		ret = true;
 	}

fs/io-wq.h

@@ -12,6 +12,7 @@ enum {
 	IO_WQ_WORK_UNBOUND	= 32,
 	IO_WQ_WORK_INTERNAL	= 64,
 	IO_WQ_WORK_CB		= 128,
+	IO_WQ_WORK_NO_CANCEL	= 256,
 
 	IO_WQ_HASH_SHIFT	= 24,	/* upper 8 bits are used for hash key */
 };

fs/io_uring.c

@@ -3460,8 +3460,11 @@ static void io_wq_submit_work(struct io_wq_work **workptr)
 	struct io_kiocb *nxt = NULL;
 	int ret = 0;
 
-	if (work->flags & IO_WQ_WORK_CANCEL)
+	/* if NO_CANCEL is set, we must still run the work */
+	if ((work->flags & (IO_WQ_WORK_CANCEL|IO_WQ_WORK_NO_CANCEL)) ==
+				IO_WQ_WORK_CANCEL) {
 		ret = -ECANCELED;
+	}
 
 	if (!ret) {
 		req->has_user = (work->flags & IO_WQ_WORK_HAS_MM) != 0;