Re: [PATCH v3 5/6] staging: r8188eu: add error handling of rtw_read32

From: Pavel Skripkin <paskripkin@gmail.com>
To: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
Cc: David Laight <David.Laight@aculab.com>,
	"Larry.Finger@lwfinger.net" <Larry.Finger@lwfinger.net>,
	"phil@philpotter.co.uk" <phil@philpotter.co.uk>,
	"straube.linux@gmail.com" <straube.linux@gmail.com>,
	"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>
Subject: Re: [PATCH v3 5/6] staging: r8188eu: add error handling of rtw_read32
Date: Fri, 27 Aug 2021 10:16:57 +0300	[thread overview]
Message-ID: <014d213d-b038-f40f-80b0-f1d5adbdf947@gmail.com> (raw)
In-Reply-To: <YSiQXpzswaRhvD4P@kroah.com>

On 8/27/21 10:12 AM, gregkh@linuxfoundation.org wrote:
> On Thu, Aug 26, 2021 at 11:03:04PM +0300, Pavel Skripkin wrote:
>> 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?
> 
> Yes it is, for when it is not needed.
> 
>> Greg, what your opinion about this NULL check?
> 
> Never check for things that you know are not going to happen.  Otherwise
> the kernel would just be full of pointless checks everywhere.
> 
> And why are you waiting for me to tell you this?  Why do you not believe
> David?
> 

Just wanted to hear more opinions on this check. I believe David, but 
opinions of other people are important too, IMO

With regards,
Pavel Skripkin