Patch "ext4: bugfix for mmaped pages in mpage_release_unused_pages()" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

ext4: bugfix for mmaped pages in mpage_release_unused_pages()

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ext4-bugfix-for-mmaped-pages-in-mpage_release_unused_pages.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: wangguang <[email protected]>
Date: Thu, 15 Sep 2016 11:32:46 -0400
Subject: ext4: bugfix for mmaped pages in mpage_release_unused_pages()
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From: wangguang <[email protected]>

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:

（1） mmap a file in ext4

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

（2） 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);

(3）Unmap the addr cause warning at

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

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

---
 fs/ext4/inode.c |    2 ++
 1 file changed, 2 insertions(+)

@@ -1649,6 +1649,8 @@ 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_SIZE);
 				ClearPageUptodate(page);
 			}

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/ext4-bugfix-for-mmaped-pages-in-mpage_release_unused_pages.patch