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    SubjectRe: fs_stack/eCryptfs: remove 3rd arg of copy_attr_all, add locking to copy_inode_size
    On Thu, 3 Apr 2008, Erez Zadok wrote:
    > In message <>, "Josef 'Jeff' Sipek" writes:
    > > I think you need to check CONFIG_PREEMPT as well.
    > I'm not sure if it's needed in case of CONFIG_PREEMPT. Anyone? The code
    > for i_size_write (below), and the comment at the top of the function,
    > suggest that the spinlock is needed only to prevent the lots seqcount.


    > BTW, some time ago I reviewed all callers of i_size_write. I did so again
    > just now, and the results were the same:
    > - a LOT of callers of i_size_write don't take any lock

    They mostly know that i_mutex is already held (as i_size_write comment
    mentions); but I believe that's up to the individual filesystem.

    > - some take another spinlock in a different data structure
    > - those that do take the spinlock, do so unconditionally
    > - only unionfs and fs/stack.c wrap the spinlock in
    > #if BITS_PER_LONG == 32 && defined(CONFIG_SMP)

    I chose to follow the #ifdeffery of i_size_write(),
    but you could do it unconditionally if you prefer:
    just a little more overhead when it's not needed.

    As I've said elsewhere, I don't think the result can be entirely
    safe against concurrent changes in the lower filesystem, using
    different locking; but I don't know how resilient unionfs is
    expected to be against messing directly with lower at the same
    time as upper level.


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