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

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Message-ID: <bffcc7d513e186734d224bda6afdd55033b451de.camel@perches.com>
Date:   Tue, 28 Jul 2020 02:11:26 -0700
From:   Joe Perches <joe@...ches.com>
To:     "wanghai (M)" <wanghai38@...wei.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

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.