netdev - Re: [PATCH] usbnet: drop unneeded check for NULL

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Date:	Wed, 5 Sep 2012 06:47:12 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	oliver@...kum.org, netdev@...r.kernel.org
Subject: Re: [PATCH] usbnet: drop unneeded check for NULL

On Tue, Sep 04, 2012 at 12:37:40PM -0400, David Miller wrote:
> From: Oliver Neukum <oliver@...kum.org>
> Date: Tue, 04 Sep 2012 18:13:18 +0200
> 
> > If that check is ever needed and tx_fixup not needed, the driver will oops here.
> > The check is wrong in any case.
> 
> Right, we are dealing with two different things here.
> 
> Tree-wide there was a blind set of changes to protect skb_tx_timestamp()
> calls with a NULL skb check.
> 
> But in this specific case, it's completely unnecessary.
> 
> So Oliver's change is definitely correct and I will add it to net-next

Looking at git blame on usbnet.c we see ...

    23ba0799	if (skb)
    23ba0799		skb_tx_timestamp(skb);

and reading on ...

    commit 23ba07991dad5a96a024c1b45cb602eef5f83df8
    Author: Konstantin Khlebnikov <khlebnikov@...nvz.org>
    Date:   Mon Nov 7 05:54:58 2011 +0000

    usbnet: fix oops in usbnet_start_xmit
    
    This patch fixes the bug added in commit v3.1-rc7-1055-gf9b491e
    SKB can be NULL at this point, at least for cdc-ncm.
    
    Signed-off-by: Konstantin Khlebnikov <khlebnikov@...nvz.org>
    Acked-by: Richard Cochran <richardcochran@...il.com>
    Signed-off-by: David S. Miller <davem@...emloft.net>

and finally cdc-ncm.c reveals

static void cdc_ncm_txpath_bh(unsigned long param)
{
	struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)param;

	spin_lock_bh(&ctx->mtx);
	if (ctx->tx_timer_pending != 0) {
		ctx->tx_timer_pending--;
		cdc_ncm_tx_timeout_start(ctx);
		spin_unlock_bh(&ctx->mtx);
	} else if (ctx->netdev != NULL) {
		spin_unlock_bh(&ctx->mtx);
		netif_tx_lock_bh(ctx->netdev);
		usbnet_start_xmit(NULL, ctx->netdev);
----------------------------------^^^^
		netif_tx_unlock_bh(ctx->netdev);
	}
}

and so I think the problem that the test addresses is still present,
or am I missing something?

Thanks,
Richard
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