linux-kernel - Re: [RESEND PATCH 1/1] staging:vt6655: remove checks around dev_kfree

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Date:	Thu, 16 Jul 2015 08:45:09 +0000 (GMT)
From:	Maninder Singh <maninder1.s@...sung.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	"forest@...ttletooquiet.net" <forest@...ttletooquiet.net>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"gclement@...bob.org" <gclement@...bob.org>,
	"tvboxspy@...il.com" <tvboxspy@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"joe@...ches.com" <joe@...ches.com>,
	PANKAJ MISHRA <pankaj.m@...sung.com>
Subject: Re: [RESEND PATCH 1/1] staging:vt6655: remove checks around
 dev_kfree_skb

Hi Dan,

>I hate these patches.  I have told Markus to stop sending them but he
>has issues so now I only complain when they introduce a bug.  There was
>one bug I have missed because it was a benchmark regression and I knew
>it was theoretically possible but I didn't know the code well enough to
>say which were fast paths...

>My main objection is that relying on the sanity check inside the
>function call makes the code more subtle to understand.  We know we need
>a NULL check but it is hidden away in another file.  The motivation for
>this patch you are sending is "There is a sanity check in dev_kfree_skb()
>so let's do an insane thing and save some lines of code."

>For this particular patch we assume throughout the whole driver that
>"pTDInfo->skb" can be NULL so making it inconsistent in this one place
>is wrong

Agreed,
But these changes are suggested because:-

where we are checking for (pTDInfo->skb), we are using it  in above line.
and it does not look good, thats why we should remove thse checks and i have suggested
changes.

code snippet:-
-----------------------

if (pTDInfo->skb_dma && (pTDInfo->skb_dma != pTDInfo->buf_dma))
    dma_unmap_single(&pDevice->pcid->dev, pTDInfo->skb_dma,
             pTDInfo->skb->len, DMA_TO_DEVICE);

----> In this we did not check for pTDInfo->skb

if (pTDInfo->skb)
    dev_kfree_skb(pTDInfo->skb);

But if am wrong, sorry for the patch.

Thanks,
Maninder
............