linux-kernel - RE: [PATCH v3 03/15] iommu: Always register bus notifiers

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Date:   Thu, 7 Jul 2022 06:34:36 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Robin Murphy <robin.murphy@....com>,
        "joro@...tes.org" <joro@...tes.org>
CC:     "will@...nel.org" <will@...nel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "vasant.hegde@....com" <vasant.hegde@....com>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "gerald.schaefer@...ux.ibm.com" <gerald.schaefer@...ux.ibm.com>,
        "schnelle@...ux.ibm.com" <schnelle@...ux.ibm.com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 03/15] iommu: Always register bus notifiers

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Thursday, July 7, 2022 8:21 AM
> 
> On 2022/7/6 21:43, Robin Murphy wrote:
> > On 2022-07-06 02:53, Baolu Lu wrote:
> >> On 2022/7/6 01:08, Robin Murphy wrote:
> >>>   /*
> >>>    * Use a function instead of an array here because the domain-type
> >>> is a
> >>>    * bit-field, so an array would waste memory.
> >>> @@ -152,6 +172,10 @@ static int __init iommu_subsys_init(void)
> >>>               (iommu_cmd_line & IOMMU_CMD_LINE_STRICT) ?
> >>>                   "(set via kernel command line)" : "");
> >>> +    /* If the system is so broken that this fails, it will WARN
> >>> anyway */
> >>
> >> Can you please elaborate a bit on this? iommu_bus_init() still return
> >> errors.
> >
> > Indeed, it's commenting on the fact that we don't try to clean up or
> > propagate an error value further even if it did ever manage to return
> > one. I feared that if I strip the error handling out of iommu_bus_init()
> > itself on the same reasoning, we'll just get constant patches from the
> > static checker brigade trying to add it back, so it seemed like the
> > neatest compromise to keep that decision where it's obviously in an
> > early initcall, rather than in the helper function which can be viewed
> > out of context. However, I'm happy to either expand this comment or go
> > the whole way and make iommu_bus_init() return void if you think it's
> > worthwhile.
> 
> Thanks for the explanation. It would be helpful if the comment could be
> expanded. In this case, after a long time, people will not consider it
> an oversight. :-)
> 

I'd prefer to making iommu_bus_init() return void plus expanding
the comment otherwise the question arises that if the only caller
is not interested in the return value then why bother returning it
in the first place. 😊