kernfs: invoke dir_ops while holding active ref of the target node
kernfs_dir_ops are currently being invoked without any active reference, which makes it tricky for the invoked operations to determine whether the objects associated those nodes are safe to access and will remain that way for the duration of such operations. kernfs already has active_ref mechanism to deal with this which makes the removal of a given node the synchronization point for gating the file operations. There's no reason for dir_ops to be any different. Update the dir_ops handling so that active_ref is held while the dir_ops are executing. This guarantees that while a dir_ops is executing the target nodes stay alive. As kernfs_dir_ops doesn't have any in-kernel user at this point, this doesn't affect anybody. Signed-off-by: NTejun Heo <tj@kernel.org> Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
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