linux-kernel - Re: [PATCH v2] iommu/mediatek: fix NULL pointer dereference when printing dev

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Message-ID: <20220427021308.22855-1-miles.chen@mediatek.com>
Date:   Wed, 27 Apr 2022 10:13:08 +0800
From:   Miles Chen <miles.chen@...iatek.com>
To:     <robin.murphy@....com>
CC:     <angelogioacchino.delregno@...labora.com>,
        <hverkuil-cisco@...all.nl>, <iommu@...ts.linux-foundation.org>,
        <joro@...tes.org>, <jroedel@...e.de>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <matthias.bgg@...il.com>,
        <mchehab@...nel.org>, <miles.chen@...iatek.com>, <will@...nel.org>,
        <yong.wu@...iatek.com>
Subject: Re: [PATCH v2] iommu/mediatek: fix NULL pointer dereference when printing dev_name

hi Robin,

>> -	link = device_link_add(dev, larbdev,
>> -			       DL_FLAG_PM_RUNTIME | DL_FLAG_STATELESS);
>> -	if (!link)
>> -		dev_err(dev, "Unable to link %s\n", dev_name(larbdev));
>> +	if (larbdev) {
>
>Until the MT8195 infra MMU support lands, is there ever a case where 
>it's actually valid for larbdev to be NULL? If not, I think it would be 
>a lot clearer to explicitly fail the probe here, rather than silently 
>continue and risk fatal errors, hangs, or other weird behaviour if 
>there's no guarantee that the correct LARB is powered up (plus then the 
>release callbacks wouldn't need to worry about it either).

Thanks, I will do probe fail in patch v3 and remove the release modification.

thanks,
Miles

>
>Robin.