linux-kernel - Re: [PATCH v2] x86/resctrl: fix a NULL vs IS

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Message-ID: <20200602221727.GA59412@romley-ivt3.sc.intel.com>
Date:   Tue, 2 Jun 2020 15:17:28 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Reinette Chatre <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH v2] x86/resctrl: fix a NULL vs IS_ERR() static checker
 warning

On Tue, Jun 02, 2020 at 10:36:11PM +0300, Dan Carpenter wrote:
> The callers don't expect *d_cdp to be set to an error pointer, they only
> check for NULL.  This leads to a static checker warning:
> 
>     arch/x86/kernel/cpu/resctrl/rdtgroup.c:2648 __init_one_rdt_domain()
>     warn: 'd_cdp' could be an error pointer
> 
> This would not trigger a bug in this specific case because
> __init_one_rdt_domain() calls it with a valid domain that would not have
> a negative id and thus not trigger the return of the ERR_PTR(). If this
> was a negative domain id then the call to rdt_find_domain() in
> domain_add_cpu() would have returned the ERR_PTR() much earlier and the
> creation of the domain with an invalid id would have been prevented.
> 
> Even though a bug is not triggered currently the right and safe thing to
> do is to set the pointer to NULL because that is what can be checked for
> when the caller is handling the CDP and non-CDP cases.
> 
> Fixes: 52eb74339a62 ("x86/resctrl: Fix rdt_find_domain() return value and checks")

Acked-by: Fenghua Yu <fenghua.yu@...el.com>