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

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Date:   Tue, 28 Jul 2020 21:38:14 +0800
From:   "wanghai (M)" <wanghai38@...wei.com>
To:     Joe Perches <joe@...ches.com>, <dchickles@...vell.com>,
        <sburla@...vell.com>, <fmanlunas@...vell.com>,
        <davem@...emloft.net>, <kuba@...nel.org>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: 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.
>>>>    		if (!dispatch) {
>>>>    			dev_err(&oct->pci_dev->dev,
>>>>    				"No memory to add dispatch function\n");
>>> And this dev_err is unnecessary.
>>>
>>>
>> I don't understand why dev_err is not needed here. We can easily know
>> that an error has occurred here through dev_err
> Memory allocation failures without __GFP_NOWARN. already
> do a dump_stack to show the location of the code that
> could not successfully allocate memory.
>
>
Thanks for your explanation. I got it.

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;

> .
>