lightnvm: pblk: schedule if data is not ready

When user threads place data into the write buffer, they reserve space
and do the memory copy out of the lock. As a consequence, when the write
thread starts persisting data, there is a chance that it is not copied
yet. In this case, avoid polling, and schedule before retrying.
Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <matias@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/lightnvm/pblk-rb.c

@@ -578,8 +578,10 @@ unsigned int pblk_rb_read_to_bio(struct pblk_rb *rb, struct nvm_rq *rqd,
 		 */
 try:
 		flags = READ_ONCE(entry->w_ctx.flags);
-		if (!(flags & PBLK_WRITTEN_DATA))
+		if (!(flags & PBLK_WRITTEN_DATA)) {
+			io_schedule();
 			goto try;
+		}
 
 		page = virt_to_page(entry->data);
 		if (!page) {