[PATCH 3.16 046/306] ext4: bugfix for mmaped pages in mpage_release_unused_pages()

[Ben Hutchings]

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

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

From: wangguang <wang.guang55@xxxxxxxxxx>

commit 4e800c0359d9a53e6bf0ab216954971b2515247f upstream.

Pages clear buffers after ext4 delayed block allocation failed,
However, it does not clean its pte_dirty flag.
if the pages unmap ,in cording to the pte_dirty ,
unmap_page_range may try to call __set_page_dirty,

which may lead to the bugon at
mpage_prepare_extent_to_map:head = page_buffers(page);.

This patch just call clear_page_dirty_for_io to clean pte_dirty
at mpage_release_unused_pages for pages mmaped.

Steps to reproduce the bug:

ï1ï mmap a file in ext4
	addr = (char *)mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED,
	       	            fd, 0);
	memset(addr, 'i', 4096);

ï2ï return EIO at

	ext4_writepages->mpage_map_and_submit_extent->mpage_map_one_extent

which causes this log message to be print:

                ext4_msg(sb, KERN_CRIT,
                        "Delayed block allocation failed for "
                        "inode %lu at logical offset %llu with"
                        " max blocks %u with error %d",
                        inode->i_ino,
                        (unsigned long long)map->m_lblk,
                        (unsigned)map->m_len, -err);

(3ïUnmap the addr cause warning at

	__set_page_dirty:WARN_ON_ONCE(warn && !PageUptodate(page));

(4) wait for a minute,then bugon happen.

Signed-off-by: wangguang <wangguang03@xxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/ext4/inode.c | 2 ++
 1 file changed, 2 insertions(+)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1494,6 +1494,8 @@ static void mpage_release_unused_pages(s
 			BUG_ON(!PageLocked(page));
 			BUG_ON(PageWriteback(page));
 			if (invalidate) {
+				if (page_mapped(page))
+					clear_page_dirty_for_io(page);
 				block_invalidatepage(page, 0, PAGE_CACHE_SIZE);
 				ClearPageUptodate(page);
 			}