[PATCH 3.16 115/204] fs/mpage.c: fix mpage_writepage() for pages with buffers

[Ben Hutchings]

3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Matthew Wilcox <willy@xxxxxxxxxxxxx>

commit f892760aa66a2d657deaf59538fb69433036767c upstream.

When using FAT on a block device which supports rw_page, we can hit
BUG_ON(!PageLocked(page)) in try_to_free_buffers().  This is because we
call clean_buffers() after unlocking the page we've written.  Introduce
a new clean_page_buffers() which cleans all buffers associated with a
page and call it from within bdev_write_page().

[akpm@xxxxxxxxxxxxxxxxxxxx: s/PAGE_SIZE/~0U/ per Linus and Matthew]
Link: http://lkml.kernel.org/r/20171006211541.GA7409@xxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Reported-by: Toshi Kani <toshi.kani@xxxxxxx>
Reported-by: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
Tested-by: Toshi Kani <toshi.kani@xxxxxxx>
Acked-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/block_dev.c              |  6 ++++--
 fs/mpage.c                  | 14 +++++++++++---
 include/linux/buffer_head.h |  1 +
 3 files changed, 16 insertions(+), 5 deletions(-)

--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -419,10 +419,12 @@ int bdev_write_page(struct block_device
 		return -EOPNOTSUPP;
 	set_page_writeback(page);
 	result = ops->rw_page(bdev, sector + get_start_sect(bdev), page, rw);
-	if (result)
+	if (result) {
 		end_page_writeback(page);
-	else
+	} else {
+		clean_page_buffers(page);
 		unlock_page(page);
+	}
 	return result;
 }
 EXPORT_SYMBOL_GPL(bdev_write_page);
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -457,6 +457,16 @@ static void clean_buffers(struct page *p
 		try_to_free_buffers(page);
 }
 
+/*
+ * For situations where we want to clean all buffers attached to a page.
+ * We don't need to calculate how many buffers are attached to the page,
+ * we just need to specify a number larger than the maximum number of buffers.
+ */
+void clean_page_buffers(struct page *page)
+{
+	clean_buffers(page, ~0U);
+}
+
 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
 		      void *data)
 {
@@ -594,10 +604,8 @@ alloc_new:
 	if (bio == NULL) {
 		if (first_unmapped == blocks_per_page) {
 			if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
-								page, wbc)) {
-				clean_buffers(page, first_unmapped);
+								page, wbc))
 				goto out;
-			}
 		}
 		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 				bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -222,6 +222,7 @@ int generic_write_end(struct file *, str
 				loff_t, unsigned, unsigned,
 				struct page *, void *);
 void page_zero_new_buffers(struct page *page, unsigned from, unsigned to);
+void clean_page_buffers(struct page *page);
 int cont_write_begin(struct file *, struct address_space *, loff_t,
 			unsigned, unsigned, struct page **, void **,
 			get_block_t *, loff_t *);