bugfix-for-mmaped-pages-in-mpage_release_unused_pages

   1 ext4: bugfix for mmaped pages in mpage_release_unused_pages()
   2
   3 From: wangguang <wang.guang55@zte.com.cn>
   4
   5 Pages clear buffers after ext4 delayed block allocation failed,
   6 However, it does not clean its pte_dirty flag.
   7 if the pages unmap ,in cording to the pte_dirty ,
   8 unmap_page_range may try to call __set_page_dirty,
   9
  10 which may lead to the bugon at
  11 mpage_prepare_extent_to_map:head = page_buffers(page);.
  12
  13 This patch just call clear_page_dirty_for_io to clean pte_dirty
  14 at mpage_release_unused_pages for pages mmaped.
  15
  16 Steps to reproduce the bug:
  17
  18 （1） mmap a file in ext4
  19         addr = (char *)mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED,
  20                             fd, 0);
  21         memset(addr, 'i', 4096);
  22
  23 （2） return EIO at
  24
  25         ext4_writepages->mpage_map_and_submit_extent->mpage_map_one_extent
  26
  27 which causes this log message to be print:
  28
  29                 ext4_msg(sb, KERN_CRIT,
  30                         "Delayed block allocation failed for "
  31                         "inode %lu at logical offset %llu with"
  32                         " max blocks %u with error %d",
  33                         inode->i_ino,
  34                         (unsigned long long)map->m_lblk,
  35                         (unsigned)map->m_len, -err);
  36
  37 (3）Unmap the addr cause warning at
  38
  39         __set_page_dirty:WARN_ON_ONCE(warn && !PageUptodate(page));
  40
  41 (4) wait for a minute,then bugon happen.
  42
  43 Signed-off-by: wangguang <wangguang03@zte.com>
  44 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  45
  46
  47 ---
  48  fs/ext4/inode.c | 2 ++
  49  1 file changed, 2 insertions(+)
  50
  51 diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
  52 index f058afb..9b464e5 100644
  53 --- a/fs/ext4/inode.c
  54 +++ b/fs/ext4/inode.c
  55 @@ -1649,6 +1649,8 @@ static void mpage_release_unused_pages(struct mpage_da_data *mpd,
  56                         BUG_ON(!PageLocked(page));
  57                         BUG_ON(PageWriteback(page));
  58                         if (invalidate) {
  59 +                               if (page_mapped(page))
  60 +                                       clear_page_dirty_for_io(page);
  61                                 block_invalidatepage(page, 0, PAGE_SIZE);
  62                                 ClearPageUptodate(page);
  63                         }