Re: Problem with dev_kfree_skb_any() in 2.6.0

From: David S. Miller (davem_at_redhat.com)
Date: 12/30/03

  • Next message: Gene Heskett: "Re: [PATCH] drivers/cdrom/sjcd.c check_region() fix" 
    Date:	Mon, 29 Dec 2003 22:01:22 -0800
To: Jeff Garzik <jgarzik@pobox.com>

    On Tue, 30 Dec 2003 00:15:19 -0500
    Jeff Garzik <jgarzik@pobox.com> wrote:

    > OK, agreed. But fixing it in the driver is still incorrect, also.
    >
    > We need a single solution in the net stack, not a per-driver solution.

    I totally disagree.

    Let's quickly review, this is illegal:

            local_irq_disable();
            {
                    local_bh_disable();
                    ... do kfree_skb work ...
                    local_bh_enable();
            }
            local_irq_enable();

    as is this:

            local_irq_disable();
            {
                    ... queue to softirq TX work ...
            }
            local_irq_enable();
            ... oops this won't make softirq TX work get run ...

    The driver must therefore recognize that it may only free packets
    in it's IRQ handler or in situations where BH protection has occurred
    at a higher level or BH protection is the only protection it uses
    from base context.

    This is similar to how the driver must be aware that
    netif_receive_skb() can cause it's ->hard_start_xmit() method to run
    and therefore it must prevent deadlocks that might occur as a result
    of locks held during the netif_receive_skb() call.

    So let's fix the drivers. :)
    -
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  • Next message: Gene Heskett: "Re: [PATCH] drivers/cdrom/sjcd.c check_region() fix"

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