Revert "ext4: Stop trying writing pages if no free blocks generated"

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7CBCS


CVE: NA

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

This reverts commit 07a8109d.

When ext4 runs out of space, there could be a potential data lost in
ext4_writepages:
If there are many preallocated blocks for some files, e4b bitmap is
different from block bitmap, and there are more free blocks accounted
by block bitmap.

    ext4_writepages                         P2
ext4_mb_new_blocks                  ext4_map_blocks
 ext4_mb_regular_allocator // No free bits in e4b bitmap
 ext4_mb_discard_preallocations_should_retry
  ext4_mb_discard_preallocations
   ext4_mb_discard_group_preallocations
    ext4_mb_release_inode_pa // updates e4b bitmap by pa->pa_free
     mb_free_blocks
                                     ext4_mb_new_blocks
                                      ext4_mb_regular_allocator
                                      // Got e4b bitmap's free bits
 ext4_mb_regular_allocator  // After 3 times retrying, ret ENOSPC

ext4_writepages
 mpage_map_and_submit_extent
  mpage_map_one_extent // ret ENOSPC
  if (err == -ENOSPC && EXT4_SB(sb)->s_mb_free_pending)
  // s_mb_free_pending is 0
  *give_up_on_write = true  // Abandon writeback, data lost!

Fixes: 07a8109d ("ext4: Stop trying writing pages if no free ...")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>