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Subject: Re: [PATCH v3 5/6] staging: r8188eu: add error handling of rtw_read32
To:     David Laight <David.Laight@ACULAB.COM>
Cc:     "Larry.Finger@lwfinger.net" <Larry.Finger@lwfinger.net>,
        "phil@philpotter.co.uk" <phil@philpotter.co.uk>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
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        "fmdefrancesco@gmail.com" <fmdefrancesco@gmail.com>,
        "linux-staging@lists.linux.dev" <linux-staging@lists.linux.dev>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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From:   Pavel Skripkin <paskripkin@gmail.com>
Message-ID: <fb29e9f2-3662-c365-7427-a91a298ef10f@gmail.com>
Date:   Thu, 26 Aug 2021 23:03:04 +0300
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On 8/26/21 1:59 PM, David Laight wrote:
> From: Pavel Skripkin
>> Sent: 26 August 2021 11:55
>> 
>> On 8/26/21 1:22 PM, David Laight wrote:
>> > From: Pavel Skripkin
>> >> Sent: 26 August 2021 10:28
>> >>
>> >> On 8/26/21 12:22 PM, Pavel Skripkin wrote:
>> >> > On Thu, 26 Aug 2021 08:51:23 +0000
>> >> > David Laight <David.Laight@ACULAB.COM> wrote:
>> > ...
>> >> >> ...
>> >> >> > -static u32 usb_read32(struct intf_hdl *pintfhdl, u32 addr)
>> >> >> > +static int usb_read32(struct intf_hdl *pintfhdl, u32 addr, u32
>> >> >> > *data) {
>> >> >> >  	u8 requesttype;
>> >> >> >  	u16 wvalue;
>> >> >> >  	u16 len;
>> >> >> > -	__le32 data;
>> >> >> > +	int res;
>> >> >> > +	__le32 tmp;
>> >> >> > +
>> >> >> > +	if (WARN_ON(unlikely(!data)))
>> >> >> > +		return -EINVAL;
>> >> >> >
>> >> >>
>> >> >> Kill the NULL check - it is a silly coding error.
>> >> >> An OOPS is just as easy to debug.
>> >> >>
>> >> >
>> >> >
>> >> > I don't think that one single driver should kill the whole system. It's
>> >> > 100% an error, but kernel can recover from it (for example disconnect
>> >> > the driver, since it's broken).
>> >> >
>> >> >
>> >> > AFIAK, Greg and Linus do not like BUG_ONs in recoverable state...
>> >> > Correct me, if I am wrong
>> >> >
>> >> Oops, I thought about BUG_ON() instead of WARN_ON(), sorry for
>> >> confusion. My point is "we should not let the box boom".
>> >
>> >
>> > There is no point checking for NULL that just can't happen.
>> > In this case all the callers will pass the address of a local.
>> > There really is no point checking.
>> >
>> 
>> We not always read in local variable, there are few places, where we
>> read into passed buffer.
> 
> It is still a very local coding bug.
> 
> 	David
> 

Sure, but is defensive programming so bad?


Greg, what your opinion about this NULL check?


With regards,
Pavel Skripkin