[PATCH v7 21/24] iomap: Restructure iomap_readpages_actor

[Matthew Wilcox <willy@infradead.org>]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

By putting the 'have we reached the end of the page' condition at the end
of the loop instead of the beginning, we can remove the 'submit the last
page' code from iomap_readpages().  Also check that iomap_readpage_actor()
didn't return 0, which would lead to an endless loop.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/iomap/buffered-io.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index cb3511eb152a..31899e6cb0f8 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -400,15 +400,9 @@ iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length,
 		void *data, struct iomap *iomap, struct iomap *srcmap)
 {
 	struct iomap_readpage_ctx *ctx = data;
-	loff_t done, ret;
-
-	for (done = 0; done < length; done += ret) {
-		if (ctx->cur_page && offset_in_page(pos + done) == 0) {
-			if (!ctx->cur_page_in_bio)
-				unlock_page(ctx->cur_page);
-			put_page(ctx->cur_page);
-			ctx->cur_page = NULL;
-		}
+	loff_t ret, done = 0;
+
+	while (done < length) {
 		if (!ctx->cur_page) {
 			ctx->cur_page = iomap_next_page(inode, ctx->pages,
 					pos, length, &done);
@@ -418,6 +412,20 @@ iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length,
 		}
 		ret = iomap_readpage_actor(inode, pos + done, length - done,
 				ctx, iomap, srcmap);
+		done += ret;
+
+		/* Keep working on a partial page */
+		if (ret && offset_in_page(pos + done))
+			continue;
+
+		if (!ctx->cur_page_in_bio)
+			unlock_page(ctx->cur_page);
+		put_page(ctx->cur_page);
+		ctx->cur_page = NULL;
+
+		/* Don't loop forever if we made no progress */
+		if (WARN_ON(!ret))
+			break;
 	}
 
 	return done;
@@ -451,11 +459,7 @@ iomap_readpages(struct address_space *mapping, struct list_head *pages,
 done:
 	if (ctx.bio)
 		submit_bio(ctx.bio);
-	if (ctx.cur_page) {
-		if (!ctx.cur_page_in_bio)
-			unlock_page(ctx.cur_page);
-		put_page(ctx.cur_page);
-	}
+	BUG_ON(ctx.cur_page);
 
 	/*
 	 * Check that we didn't lose a page due to the arcance calling
-- 
2.25.0