Question about (or bug in?) the kobject implementation

From: Alan Stern (stern_at_rowland.harvard.edu)
Date: 02/25/04

  • Next message: Grigor Gatchev: "Re: A Layered Kernel: Proposal" 
    Date:	Wed, 25 Feb 2004 10:05:37 -0500 (EST)
To: Kernel development list <linux-kernel@vger.kernel.org>

    Is it supposed to be legal to repeatedly call kobject_add() and
    kobject_del() for the same kobject? That is, is

            kobject_add(&kobj);
            ...
            kobject_del(&kobj);
            ...
            kobject_add(&kobj);
            ...
            kobject_del(&kobj);

    supposed to work? The API doesn't forbid it, and there's no apparent
    reason why it should be illegal.

    I ask because the current implementation is set up in such a way that
    doing this will mess up the reference counting for the kobject's parent.
    The problem is that the parent's refcount is increased each time
    kobject_add() is called, but it is only decremented in kobject_cleanup(),
    not in kobject_del(). Thus, the statements above will leave the parent's
    refcount permanently increased by 1, potentially causing a memory leak.

    Why would anyone want to do this, you ask? Well the USB subsystem does it
    already. Each USB device can have several configurations, only one of
    which is active at any time. Corresponding to each configuration is a set
    of struct devices, and they (together with their embedded kobjects) are
    allocated and initialized when the USB device is first detected. The
    struct devices are add()'ed and del()'ed as configurations are activated
    and deactivated, leading to just the sort of call sequence shown above.

    Alan Stern

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  • Next message: Grigor Gatchev: "Re: A Layered Kernel: Proposal"

    Relevant Pages

    • Re: Question about (or bug in?) the kobject implementation
      ... > kobject_del() for the same kobject? ... > allocated and initialized when the USB device is first detected. ... > struct devices are add'ed and del'ed as configurations are activated ... send the line "unsubscribe linux-kernel" in ...
      (Linux-Kernel)
    • Re: Question about (or bug in?) the kobject implementation
      ... >> allocated and initialized when the USB device is first detected. ... >> struct devices are add'ed and del'ed as configurations are activated ... I have a patch to do that. ... send the line "unsubscribe linux-kernel" in ...
      (Linux-Kernel)