linux-kernel - Re: [PATCH v2] x86/xen: Add some null pointer checking to smp.c

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Date: Mon, 22 Jan 2024 11:30:02 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Kunwu Chan <chentao@...inos.cn>
Cc: Markus Elfring <Markus.Elfring@....de>, xen-devel@...ts.xenproject.org,
	kernel-janitors@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	kernel test robot <lkp@...el.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Jürgen Groß <jgross@...e.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Subject: Re: [PATCH v2] x86/xen: Add some null pointer checking to smp.c

On Fri, Jan 19, 2024 at 05:22:25PM +0800, Kunwu Chan wrote:
> On 2024/1/17 18:40, Markus Elfring wrote:
> > > kasprintf() returns a pointer to dynamically allocated memory
> > > which can be NULL upon failure. Ensure the allocation was successful
> > > by checking the pointer validity.
> > …
> > > +++ b/arch/x86/xen/smp.c
> > > @@ -61,10 +61,14 @@ void xen_smp_intr_free(unsigned int cpu)
> > > 
> > >   int xen_smp_intr_init(unsigned int cpu)
> > >   {
> > > -	int rc;
> > > +	int rc = 0;
> > 
> > I find the indication of a successful function execution sufficient by
> > the statement “return 0;” at the end.
> > How do you think about to omit such an extra variable initialisation?
> Thanks, it's no need now. I'll remove it in v3.

This advice is good.  Don't do unnecessary assignments.

> > 
> > 
> > >   	char *resched_name, *callfunc_name, *debug_name;
> > > 
> > >   	resched_name = kasprintf(GFP_KERNEL, "resched%d", cpu);
> > > +	if (!resched_name) {
> > > +		rc = -ENOMEM;
> > > +		goto fail;
> > > +	}
> > >   	per_cpu(xen_resched_irq, cpu).name = resched_name;
> > >   	rc = bind_ipi_to_irqhandler(XEN_RESCHEDULE_VECTOR,
> > >   				    cpu,
> > 
> > You propose to apply the same error code in four if branches.
> > I suggest to avoid the specification of duplicate assignment statements
> > for this purpose.
> > How do you think about to use another label like “e_nomem”?
> I'll add a new label to simply the code.

I'm not a Xen maintainer so I can't really comment on their style
choices.  However, as one of the kernel-janitors list people, I would
say that not everyone agrees with Markus's style preferences.  Markus
was banned from the list for a while, but we unbanned everyone when we
transitioned to the new list infrastructure.  Do a search on lore to
find out more.  https://lore.kernel.org/all/?q=Elfring

Perhaps wait for feedback from the maintainers for how to proceed?

regards,
dan carpenter