[PATCH 05/13] mm: simplify generic_file_buffered_read_no_cached_page

From: Christoph Hellwig <hch@lst.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Kent Overstreet <kent.overstreet@gmail.com>,
	Matthew Wilcox <willy@infradead.org>,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH 05/13] mm: simplify generic_file_buffered_read_no_cached_page
Date: Sat, 31 Oct 2020 09:59:56 +0100	[thread overview]
Message-ID: <20201031090004.452516-6-hch@lst.de> (raw)
In-Reply-To: <20201031090004.452516-1-hch@lst.de>

Return an errno and add a new by reference argument for the allocated
page, which allows to cleanup the error unwindining in the function
and the caller.  Also rename the function to filemap_new_page which is
both shorter and more descriptive.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 mm/filemap.c | 53 ++++++++++++++++------------------------------------
 1 file changed, 16 insertions(+), 37 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 5cdf8090d4e12c..9e1cc18afe1134 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2300,41 +2300,27 @@ static int filemap_make_page_uptodate(struct kiocb *iocb, struct iov_iter *iter,
 	return error;
 }
 
-static struct page *
-generic_file_buffered_read_no_cached_page(struct kiocb *iocb,
-					  struct iov_iter *iter)
+static int filemap_new_page(struct kiocb *iocb, struct iov_iter *iter,
+		struct page **page)
 {
-	struct file *filp = iocb->ki_filp;
-	struct address_space *mapping = filp->f_mapping;
+	struct address_space *mapping = iocb->ki_filp->f_mapping;
+	gfp_t gfp = mapping_gfp_constraint(mapping, GFP_KERNEL);
 	pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
-	struct page *page;
 	int error;
 
 	if (iocb->ki_flags & IOCB_NOIO)
-		return ERR_PTR(-EAGAIN);
+		return -EAGAIN;
 
-	/*
-	 * Ok, it wasn't cached, so we need to create a new
-	 * page..
-	 */
-	page = page_cache_alloc(mapping);
+	*page = page_cache_alloc(mapping);
 	if (!page)
-		return ERR_PTR(-ENOMEM);
-
-	error = add_to_page_cache_lru(page, mapping, index,
-				      mapping_gfp_constraint(mapping, GFP_KERNEL));
+		return -ENOMEM;
+	error = add_to_page_cache_lru(*page, mapping, index, gfp);
 	if (error) {
-		put_page(page);
-		return error != -EEXIST ? ERR_PTR(error) : NULL;
+		put_page(*page);
+		return error;
 	}
 
-	error = filemap_readpage(iocb, page);
-	if (error) {
-		if (error == AOP_TRUNCATED_PAGE)
-			return NULL;
-		return ERR_PTR(error);
-	}
-	return page;
+	return filemap_readpage(iocb, *page);
 }
 
 static int generic_file_buffered_read_get_pages(struct kiocb *iocb,
@@ -2366,18 +2352,14 @@ static int generic_file_buffered_read_get_pages(struct kiocb *iocb,
 	nr_got = find_get_pages_contig(mapping, index, nr, pages);
 	if (nr_got)
 		goto got_pages;
-
-	pages[0] = generic_file_buffered_read_no_cached_page(iocb, iter);
-	err = PTR_ERR_OR_ZERO(pages[0]);
-	if (!IS_ERR_OR_NULL(pages[0]))
+	err = filemap_new_page(iocb, iter, &pages[0]);
+	if (!err)
 		nr_got = 1;
 got_pages:
 	for (i = 0; i < nr_got; i++) {
 		err = filemap_make_page_uptodate(iocb, iter, pages[i],
 				index + i, i == 0);
 		if (err) {
-			if (err == AOP_TRUNCATED_PAGE)
-				err = 0;
 			for (j = i + 1; j < nr_got; j++)
 				put_page(pages[j]);
 			nr_got = i;
@@ -2387,12 +2369,9 @@ static int generic_file_buffered_read_get_pages(struct kiocb *iocb,
 
 	if (likely(nr_got))
 		return nr_got;
-	if (err)
-		return err;
-	/*
-	 * No pages and no error means we raced and should retry:
-	 */
-	goto find_page;
+	if (err == -EEXIST || err == AOP_TRUNCATED_PAGE)
+		goto find_page;
+	return err;
 }
 
 /**
-- 
2.28.0

