Use of mmap_sem in map_user_kiobuf

[Adrian Cox <adrian@humboldt.co.uk>]

Does map_user_kiobuf really need to get a write lock on the mmap_sem? 
 From examination of the code, all it can do is expand_stack(), fault in 
pages, and increment the count on a page.

Is there anything I've missed? Would it be safe to use down_read(), 
up_read() instead?

-- 
Adrian Cox   http://www.humboldt.co.uk/

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