io_uring: do not recycle buffer in READV

READV cannot recycle buffers as it would lose some of the data required to
reimport that buffer.

Reported-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Fixes: b66e65f ("io_uring: never call io_buffer_select() for a buffer re-select")
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220721131325.624788-1-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -1737,6 +1737,14 @@ static void io_kbuf_recycle(struct io_kiocb *req, unsigned issue_flags)
 	    (req->flags & REQ_F_PARTIAL_IO))
 		return;
 
+	/*
+	 * READV uses fields in `struct io_rw` (len/addr) to stash the selected
+	 * buffer data. However if that buffer is recycled the original request
+	 * data stored in addr is lost. Therefore forbid recycling for now.
+	 */
+	if (req->opcode == IORING_OP_READV)
+		return;
+
 	/*
 	 * We don't need to recycle for REQ_F_BUFFER_RING, we can just clear
 	 * the flag and hence ensure that bl->head doesn't get incremented.