ubifs: Fix 'ui->dirty' race between do_tmpfile() and writeback work

ubifs: Fix 'ui->dirty' race between do_tmpfile() and writeback work

'ui->dirty' is not protected by 'ui_mutex' in function do_tmpfile() which
may race with ubifs_write_inode[wb_workfn] to access/update 'ui->dirty',
finally dirty space is released twice.

	open(O_TMPFILE)                wb_workfn
do_tmpfile
  ubifs_budget_space(ino_req = { .dirtied_ino = 1})
  d_tmpfile // mark inode(tmpfile) dirty
  ubifs_jnl_update // without holding tmpfile's ui_mutex
    mark_inode_clean(ui)
      if (ui->dirty)
        ubifs_release_dirty_inode_budget(ui)  // release first time
                                   ubifs_write_inode
				     mutex_lock(&ui->ui_mutex)
                                     ubifs_release_dirty_inode_budget(ui)
				     // release second time
				     mutex_unlock(&ui->ui_mutex)
      ui->dirty = 0

Run generic/476 can reproduce following message easily
(See reproducer in [Link]):

  UBIFS error (ubi0:0 pid 2578): ubifs_assert_failed [ubifs]: UBIFS assert
  failed: c->bi.dd_growth >= 0, in fs/ubifs/budget.c:554
  UBIFS warning (ubi0:0 pid 2578): ubifs_ro_mode [ubifs]: switched to
  read-only mode, error -22
  Workqueue: writeback wb_workfn (flush-ubifs_0_0)
  Call Trace:
    ubifs_ro_mode+0x54/0x60 [ubifs]
    ubifs_assert_failed+0x4b/0x80 [ubifs]
    ubifs_release_budget+0x468/0x5a0 [ubifs]
    ubifs_release_dirty_inode_budget+0x53/0x80 [ubifs]
    ubifs_write_inode+0x121/0x1f0 [ubifs]
    ...
    wb_workfn+0x283/0x7b0

Fix it by holding tmpfile ubifs inode lock during ubifs_jnl_update().
Similar problem exists in whiteout renaming, but previous fix("ubifs:
Rename whiteout atomically") has solved the problem.

Fixes: 474b93704f32163 ("ubifs: Implement O_TMPFILE")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=214765
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>