On Tue 03-05-11 16:08:36, Surbhi Palande wrote:

On munmap() zap_pte_range() is called which dirties the PTE dirty pages as
Toshiyuki pointed out.

zap_pte_range()
  mapping->a_ops->set_page_dirty (= ext4_journalled_set_page_dirty)  

So, I think that it is here that we should do the checking for a ext4 F.S
frozen state and also prevent a parallel ext4 F.S freeze from happening.

Attaching a patch for initial review. Please do let me know your thoughts! 

  This is definitely the wrong place. ->set_page_dirty() callbacks are
called with various locks held and the page need not be locked (thus
dereferencing page->mapping is oopsable). Moreover this particular callback
is called only in data=journal mode.

Believe me, the right place is page_mkwrite() - you have to catch the
read-only => read-write page transition. Once the page is mapped
read-write, you've already lost the race.

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR