get_empty_filp

[Lee Chin]

Hello All,
I am seeing a bug in get_empty_filp (fs/file_table.c) where
files_stat.nr_free_files is out of sync with respect to the actual number of
elements in free_list.

More precicely, for some reason, free_list became empty (free_list.next and
free_list.prev pointed back to free_list) but files_stat.nr_free_files was
180.  So the code list_entry(free_list.next...) returned a bad pointer (in
this case a pointer to free_list) and the memset in the get_empty_filp
overwrote the files_lock.

As far as I can see, one way this can happen is if in _fput, the list_del
and list_add routines took the *file off of teh free_list and put it back on
the free_list, causing the statement files_stat.nr_free_files++ to be out of
sync.

My question is... can anyone call _fput where the *file parameter is already
on the free_list?

Thanks
Lee

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