linux-kernel - Re: [PATCH] wlcore: consolidate kmalloc + memset 0 into kzalloc

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Message-ID: <20151222072951.GA31496@osadl.at>
Date:	Tue, 22 Dec 2015 07:29:51 +0000
From:	Nicholas Mc Guire <der.herr@...r.at>
To:	Julian Calaby <julian.calaby@...il.com>
Cc:	Nicholas Mc Guire <hofrat@...dl.org>,
	Kalle Valo <kvalo@...eaurora.org>,
	Eliad Peller <eliad@...ery.com>,
	Johannes Berg <johannes.berg@...el.com>,
	Arik Nemtsov <arik@...ery.com>,
	Tony Lindgren <tony@...mide.com>,
	Luciano Coelho <luca@...lho.fi>,
	Eyal Reizer <eyalreizer@...il.com>,
	Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] wlcore: consolidate kmalloc + memset 0 into kzalloc

On Tue, Dec 22, 2015 at 09:56:10AM +1100, Julian Calaby wrote:
> Hi,
> 
> On Tue, Dec 22, 2015 at 3:47 AM, Nicholas Mc Guire <hofrat@...dl.org> wrote:
> > This is an API consolidation only. The use of kmalloc + memset to 0
> > is equivalent to kzalloc.
> >
> > Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> > ---
> >
> > Found by coccinelle script (relaxed version of
> > scripts/coccinelle/api/alloc/kzalloc-simple.cocci)
> >
> > Patch was compile tested with: x86_64_defconfig +
> > CONFIG_WL12XX=m (implies CONFIG_WLCORE=m)
> >
> > Patch is against linux-next (localversion-next is -next-20151221)
> >
> >  drivers/net/wireless/ti/wlcore/main.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/wireless/ti/wlcore/main.c b/drivers/net/wireless/ti/wlcore/main.c
> > index ec7f6af..dfc49bf 100644
> > --- a/drivers/net/wireless/ti/wlcore/main.c
> > +++ b/drivers/net/wireless/ti/wlcore/main.c
> > @@ -838,7 +838,7 @@ static void wl12xx_read_fwlog_panic(struct wl1271 *wl)
> >
> >         wl1271_info("Reading FW panic log");
> >
> > -       block = kmalloc(wl->fw_mem_block_size, GFP_KERNEL);
> > +       block = kzalloc(wl->fw_mem_block_size, GFP_KERNEL);
> >         if (!block)
> >                 return;
> >
> > @@ -885,7 +885,6 @@ static void wl12xx_read_fwlog_panic(struct wl1271 *wl)
> >                         goto out;
> >                 }
> > -               memset(block, 0, wl->fw_mem_block_size);
> 
> I don't think you can't remove this line. It appears that the loop
> this is part of resets block to be all zero, reads a chunk of data in,
> then operates on it. I'm guessing that the code after the following
> line expects that there isn't any data left over from previous runs
> through the loop.
>
the rational for this being ok is thta the copy operation into block is: 
                ret = wlcore_read_hwaddr(wl, addr, block,
                                        wl->fw_mem_block_size, false);

this will end up in the .read methods where block should be completely 
overwritten (length == full block size), so within the loop if successful
this should be correct - if not successful it would "goto out" witout 
using the content of block.

Am I overlooking something here ?

thx!
hofrat
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