On 08/14, David Hildenbrand wrote:
>
> >OK, I seem to understand... without mmap_read_lock() it is possible that
> >
> > - dup_mm_exe_file() sees mm->exe_file = old_exe_file
> >
> > - replace_mm_exe_file() does allow_write_access(old_exe_file)
> >
> > - another process does get_write_access(old_exe_file)
> >
> > - dup_mm_exe_file()->deny_write_access() fails
> >
> >Right?
>
> From what I recall, yes.
Thanks! but then... David, this all is subjective, feel free to ignore, but
the current code doesn't look good to me, I mean the purpose of mmap_read_lock()
is very unclear. To me something like
if (old_exe_file) {
/*
* Ensure that if we race with dup_mm_exe_file() and it sees
* mm->exe_file == old_exe_file deny_write_access(old_exe_file)
* can't fail after we do allow_write_access() and another task
* does get_write_access(old_exe_file).
*/
mmap_read_lock(mm);
mmap_read_unlock(mm);
allow_write_access(old_exe_file);
fput(old_exe_file);
}
looks more understandable...
But this patch from Mateusz looks even better to me. So, FWIW,
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
