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    SubjectRe: [PATCH 04/24] sysfs: Normalize removing sysfs directories.
    Tejun Heo <> writes:

    > Eric W. Biederman wrote:
    >> Also, I'm quite uncomfortable with these things
    >>> being done in non-atomic manner. It can be made to work but things
    >>> like this can lead to subtle race conditions and with the kind of
    >>> layering we put on top of sysfs (kobject, driver model, driver
    >>> midlayers and so on), it isn't all that easy to verify what's going
    >>> on, so NACK for this one.
    >> Total nonsense.
    >> Mucking about with sysfs after we start deleting a directory is a bug.
    >> At worst my change makes a buggy race slightly less deterministic.
    >> I am not ready to consider keeping the current unnecessary atomic
    >> removal step. That unnecessary atomicity makes the following patches
    >> more difficult, and requires a lot of unnecessary retesting.
    >> What do you think the extra unnecessary atomicity helps protect?
    > It's just not a clean API. When people are trying to code things way
    > up in the stack, they aren't likely to look up the code to see what
    > assumptions are being made especially when the stack is deep and
    > complex and sysfs is near the bottom of the tall stack. IMHO
    > implementing the usually expected semantics at this depth is worth
    > every effort. It's just good implementation style which might look
    > like wasted effort but will harden the stack in the long run. Plus,
    > it's not like making it atomic is difficult or anything.

    I guess we are going to have to disagree on this one.

    My take is simply that a correct user has to wait until no one else
    can find the kobject before calling kobject_del. At which point
    races are impossible, and it doesn't matter if sysfs_mutex is held
    across the entire operation.

    For the long term I still intend to kill __sysfs_remove_dir. Just
    not in this patch series.


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      Last update: 2009-05-30 15:11    [W:0.025 / U:17.296 seconds]
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