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    SubjectRe: [PATCH 04/13] fsnotify: add in inode fsnotify markings
    On Thu, Mar 19, 2009 at 02:05:14PM -0400, Eric Paris wrote:
    > This patch creates in inode fsnotify markings. dnotify will make use of in
    > inode markings to mark which inodes it wishes to send events for. fanotify
    > will use this to mark which inodes it does not wish to send events for.

    Hrm... What happens if fsnotify_clear_marks_by_inode() is called, gets
    the only mark we had for a group, removes it from all lists, drops all
    locks and races with the final fsnotify_put_group()? Said put_group
    sees nothing whatsoever on the per-group mark list (the only mark we
    used to have there is already evicted) and the group is cheerfully
    freed. Then fsnotify_destroy_mark_by_entry() calls
    group->ops->freeing_mark(entry, group)
    with group already freed... Gets really interesting in case of inotify -
    there ->freeing_mark() leads to blocking allocations and really touches
    group in non-trivial ways.

    Note that for inotify ->freeing_mark() will happily add notification to
    group's queue and that's another race of the same nature - even if
    group itself isn't yet freed, that final put_group() might bloody well
    get past flushing the queue.

    I really don't like the idea of having marks contributing to group refcount -
    that would have solved this one, but we'd get potential leaks from hell ;-/
    Maybe a separate counter controlling only actual freeing of group?


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