linux-kernel - Re: [PATCH v3 04/11] net: qrtr: support identical node ids

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Message-ID: <20250804095522.GP8494@horms.kernel.org>
Date: Mon, 4 Aug 2025 10:55:22 +0100
From: Simon Horman <horms@...nel.org>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Mihai Moldovan <ionic@...ic.de>, linux-arm-msm@...r.kernel.org,
	Manivannan Sadhasivam <mani@...nel.org>,
	Denis Kenzior <denkenz@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Kuniyuki Iwashima <kuniyu@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Willem de Bruijn <willemb@...gle.com>,
	"David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH v3 04/11] net: qrtr: support identical node ids

On Fri, Aug 01, 2025 at 08:25:58PM +0300, Dan Carpenter wrote:
> On Sun, Jul 27, 2025 at 03:40:14PM +0100, Simon Horman wrote:
> > + Dan Carpenter
> > 
> > On Sun, Jul 27, 2025 at 03:09:38PM +0200, Mihai Moldovan wrote:
> > > * On 7/24/25 15:08, Simon Horman wrote:

...

> > This seems to a regression in Smatch wrt this particular case for this
> > code. I bisected Smatch and it looks like it was introduced in commit
> > d0367cd8a993 ("ranges: use absolute instead implied for possibly_true/false")
> > 
> > I CCed Dan in case he wants to dig into this.
> 
> The code looks like this:
> 
> 	spin_lock_irqsave(&qrtr_nodes_lock, flags);
> 
>         if (node->ep->id > QRTR_INDEX_HALF_UNSIGNED_MAX ||
>             nid > QRTR_INDEX_HALF_UNSIGNED_MAX)
>                 return -EINVAL;
> 
> The problem is that QRTR_INDEX_HALF_UNSIGNED_MAX is U32_MAX and
> node->ep->id and nid are both u32 type.  The return statement is dead
> code and I deliberately silenced warnings on impossible paths.
> 
> The following patch will enable the warning again and I'll test it tonight
> to see what happens.  If it's not too painful then I'll delete it
> properly, but if it's generates a bunch of false positives then, in the
> end, I'm not overly stressed about bugs in dead code.

Thanks Dan,

I think the key point here is that neither Mihai nor I noticed
the dead code. Thanks for pointing that out.

...