Merge tag 'io_uring-6.12-20241011' of git://git.kernel.dk/linux

Pull io_uring fixes from Jens Axboe:

 - Explicitly have a mshot_finished condition for IORING_OP_RECV in
   multishot mode, similarly to what IORING_OP_RECVMSG has. This doesn't
   fix a bug right now, but it makes it harder to actually have a bug
   here if a request takes multiple iterations to finish.

 - Fix handling of retry of read/write of !FMODE_NOWAIT files. If they
   are pollable, that's all we need.

* tag 'io_uring-6.12-20241011' of git://git.kernel.dk/linux:
  io_uring/rw: allow pollable non-blocking attempts for !FMODE_NOWAIT
  io_uring/rw: fix cflags posting for single issue multishot read

Author: torvalds

io_uring/rw.c

@@ -31,9 +31,19 @@ struct io_rw {
 	rwf_t				flags;
 };
 
-static inline bool io_file_supports_nowait(struct io_kiocb *req)
+static bool io_file_supports_nowait(struct io_kiocb *req, __poll_t mask)
 {
-	return req->flags & REQ_F_SUPPORT_NOWAIT;
+	/* If FMODE_NOWAIT is set for a file, we're golden */
+	if (req->flags & REQ_F_SUPPORT_NOWAIT)
+		return true;
+	/* No FMODE_NOWAIT, if we can poll, check the status */
+	if (io_file_can_poll(req)) {
+		struct poll_table_struct pt = { ._key = mask };
+
+		return vfs_poll(req->file, &pt) & mask;
+	}
+	/* No FMODE_NOWAIT support, and file isn't pollable. Tough luck. */
+	return false;
 }
 
 #ifdef CONFIG_COMPAT
@@ -796,8 +806,8 @@ static int io_rw_init_file(struct io_kiocb *req, fmode_t mode, int rw_type)
 	 * supports async. Otherwise it's impossible to use O_NONBLOCK files
 	 * reliably. If not, or it IOCB_NOWAIT is set, don't retry.
 	 */
-	if ((kiocb->ki_flags & IOCB_NOWAIT) ||
-	    ((file->f_flags & O_NONBLOCK) && !io_file_supports_nowait(req)))
+	if (kiocb->ki_flags & IOCB_NOWAIT ||
+	    ((file->f_flags & O_NONBLOCK && (req->flags & REQ_F_SUPPORT_NOWAIT))))
 		req->flags |= REQ_F_NOWAIT;
 
 	if (ctx->flags & IORING_SETUP_IOPOLL) {
@@ -838,7 +848,7 @@ static int __io_read(struct io_kiocb *req, unsigned int issue_flags)
 
 	if (force_nonblock) {
 		/* If the file doesn't support async, just async punt */
-		if (unlikely(!io_file_supports_nowait(req)))
+		if (unlikely(!io_file_supports_nowait(req, EPOLLIN)))
 			return -EAGAIN;
 		kiocb->ki_flags |= IOCB_NOWAIT;
 	} else {
@@ -951,13 +961,6 @@ int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags)
 
 	ret = __io_read(req, issue_flags);
 
-	/*
-	 * If the file doesn't support proper NOWAIT, then disable multishot
-	 * and stay in single shot mode.
-	 */
-	if (!io_file_supports_nowait(req))
-		req->flags &= ~REQ_F_APOLL_MULTISHOT;
-
 	/*
 	 * If we get -EAGAIN, recycle our buffer and just let normal poll
 	 * handling arm it.
@@ -972,14 +975,15 @@ int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags)
 		if (issue_flags & IO_URING_F_MULTISHOT)
 			return IOU_ISSUE_SKIP_COMPLETE;
 		return -EAGAIN;
-	}
-
-	/*
-	 * Any successful return value will keep the multishot read armed.
-	 */
-	if (ret > 0 && req->flags & REQ_F_APOLL_MULTISHOT) {
+	} else if (ret <= 0) {
+		io_kbuf_recycle(req, issue_flags);
+		if (ret < 0)
+			req_set_fail(req);
+	} else {
 		/*
-		 * Put our buffer and post a CQE. If we fail to post a CQE, then
+		 * Any successful return value will keep the multishot read
+		 * armed, if it's still set. Put our buffer and post a CQE. If
+		 * we fail to post a CQE, or multishot is no longer set, then
 		 * jump to the termination path. This request is then done.
 		 */
 		cflags = io_put_kbuf(req, ret, issue_flags);
@@ -1026,7 +1030,7 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
 
 	if (force_nonblock) {
 		/* If the file doesn't support async, just async punt */
-		if (unlikely(!io_file_supports_nowait(req)))
+		if (unlikely(!io_file_supports_nowait(req, EPOLLOUT)))
 			goto ret_eagain;
 
 		/* Check if we can support NOWAIT. */