io_uring: commit non-pollable provided mapped buffers upfront

For recv/recvmsg, IO either completes immediately or gets queued for a
retry. This isn't the case for read/readv, if eg a normal file or a block
device is used. Here, an operation can get queued with the block layer.
If this happens, ring mapped buffers must get committed immediately to
avoid that the next read can consume the same buffer.

Check if we're dealing with pollable file, when getting a new ring mapped
provided buffer. If it's not, commit it immediately rather than wait post
issue. If we don't wait, we can race with completions coming in, or just
plain buffer reuse by committing after a retry where others could have
grabbed the same buffer.

Fixes: c7fb194 ("io_uring: add support for ring mapped supplied buffers")
Reviewed-by: Hao Xu <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

fs/io_uring.c

@@ -3836,7 +3836,7 @@ static void __user *io_ring_buffer_select(struct io_kiocb *req, size_t *len,
 	req->buf_list = bl;
 	req->buf_index = buf->bid;
 
-	if (issue_flags & IO_URING_F_UNLOCKED) {
+	if (issue_flags & IO_URING_F_UNLOCKED || !file_can_poll(req->file)) {
 		/*
 		 * If we came in unlocked, we have no choice but to consume the
 		 * buffer here. This does mean it'll be pinned until the IO