linux-kernel - Re: [PATCH 01/14] pch_uart: drop double zeroing

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Date:   Sun, 27 Sep 2020 14:11:36 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Julia Lawall <julia.lawall@...ia.fr>
Cc:     kernel-janitors@...r.kernel.org, Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/14] pch_uart: drop double zeroing

On Sun, Sep 20, 2020 at 02:47:11PM +0200, Julia Lawall wrote:
> 
> 
> On Sun, 20 Sep 2020, Greg Kroah-Hartman wrote:
> 
> > On Sun, Sep 20, 2020 at 01:26:13PM +0200, Julia Lawall wrote:
> > > sg_init_table zeroes its first argument, so the allocation of that argument
> > > doesn't have to.
> > >
> > > the semantic patch that makes this change is as follows:
> > > (http://coccinelle.lip6.fr/)
> > >
> > > // <smpl>
> > > @@
> > > expression x,n,flags;
> > > @@
> > >
> > > x =
> > > - kcalloc
> > > + kmalloc_array
> > >   (n,sizeof(struct scatterlist),flags)
> > > ...
> > > sg_init_table(x,n)
> > > // </smpl>
> > >
> > > Signed-off-by: Julia Lawall <Julia.Lawall@...ia.fr>
> >
> > It inits the first entry in the array, but what about all of the other
> > ones?  Is that "safe" to have uninitialized data in them like your
> > change causes to happen?
> 
> Sorry, I don't follow.  The complete code is:
> 
>         priv->sg_tx_p = kcalloc(num, sizeof(struct scatterlist), GFP_ATOMIC);
>         if (!priv->sg_tx_p) {
> 		dev_err(priv->port.dev, "%s:kzalloc Failed\n", __func__);
>                 return 0;
> 	}
> 
> 	sg_init_table(priv->sg_tx_p, num); /* Initialize SG table */
> 
> and the definition of sg_init_table is:
> 
> void sg_init_table(struct scatterlist *sgl, unsigned int nents)
> {
> 	memset(sgl, 0, sizeof(*sgl) * nents);
> 	sg_init_marker(sgl, nents);
> }

Ah, missed the "* nents" thing there, sorry, my fault.

greg k-h