linux-kernel - Re: [PATCH net-next] liquidio: Remove unneeded cast from memory allocation

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Message-ID: <BYAPR18MB24230A8301FD9849F9943B9DAC730@BYAPR18MB2423.namprd18.prod.outlook.com>
Date:   Tue, 28 Jul 2020 15:39:49 +0000
From:   Derek Chickles <dchickles@...vell.com>
To:     "wanghai (M)" <wanghai38@...wei.com>,
        Joe Perches <joe@...ches.com>,
        Satananda Burla <sburla@...vell.com>,
        Felix Manlunas <fmanlunas@...vell.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] liquidio: Remove unneeded cast from memory
 allocation

> From: wanghai (M) <wanghai38@...wei.com>
> Subject: [EXT] Re: [PATCH net-next] liquidio: Remove unneeded cast from
> memory allocation
> 
> 在 2020/7/28 17:11, Joe Perches 写道:
> > On Tue, 2020-07-28 at 16:42 +0800, wanghai (M) wrote:
> >> 在 2020/7/25 5:29, Joe Perches 写道:
> >>> On Fri, 2020-07-24 at 21:00 +0800, Wang Hai wrote:
> >>>> Remove casting the values returned by memory allocation function.
> >>>>
> >>>> Coccinelle emits WARNING:
> >>>>
> >>>> ./drivers/net/ethernet/cavium/liquidio/octeon_device.c:1155:14-36:
> WARNING:
> >>>>    casting value returned by memory allocation function to (struct
> octeon_dispatch *) is useless.
> >>> []
> >>>> diff --git a/drivers/net/ethernet/cavium/liquidio/octeon_device.c
> >>>> b/drivers/net/ethernet/cavium/liquidio/octeon_device.c
> >>> []
> >>>> @@ -1152,8 +1152,7 @@ octeon_register_dispatch_fn(struct
> >>>> octeon_device *oct,
> >>>>
> >>>>    		dev_dbg(&oct->pci_dev->dev,
> >>>>    			"Adding opcode to dispatch list linked list\n");
> >>>> -		dispatch = (struct octeon_dispatch *)
> >>>> -			   vmalloc(sizeof(struct octeon_dispatch));
> >>>> +		dispatch = vmalloc(sizeof(struct octeon_dispatch));
> >>> More the question is why this is vmalloc at all as the structure
> >>> size is very small.
> >>>
> >>> Likely this should just be kmalloc.
> >>>
> >>>
> >> Thanks for your advice.  It is indeed best to use kmalloc here.

I think that is fine as well. We just used vmalloc since there is no need
for a physically contiguous piece of memory.

...

> 
> Can it be modified like this?
> 
> --- a/drivers/net/ethernet/cavium/liquidio/octeon_device.c
> +++ b/drivers/net/ethernet/cavium/liquidio/octeon_device.c
> @@ -1152,11 +1152,8 @@ octeon_register_dispatch_fn(struct
> octeon_device *oct,
> 
>                  dev_dbg(&oct->pci_dev->dev,
>                          "Adding opcode to dispatch list linked list\n");
> -               dispatch = (struct octeon_dispatch *)
> -                          vmalloc(sizeof(struct octeon_dispatch));
> +               dispatch = kmalloc(sizeof(struct octeon_dispatch),
> GFP_KERNEL);
>                  if (!dispatch) {
> -                       dev_err(&oct->pci_dev->dev,
> -                               "No memory to add dispatch function\n");
>                          return 1;
>                  }
>                  dispatch->opcode = combined_opcode;

Looks fine to me.

Thanks,
Derek