linux-kernel - RE: [PATCH v3 5/6] staging: r8188eu: add error handling of rtw

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Date:   Thu, 26 Aug 2021 08:51:23 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Pavel Skripkin' <paskripkin@...il.com>,
        "Larry.Finger@...inger.net" <Larry.Finger@...inger.net>,
        "phil@...lpotter.co.uk" <phil@...lpotter.co.uk>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "straube.linux@...il.com" <straube.linux@...il.com>,
        "fmdefrancesco@...il.com" <fmdefrancesco@...il.com>
CC:     "linux-staging@...ts.linux.dev" <linux-staging@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 5/6] staging: r8188eu: add error handling of rtw_read32

From: Pavel Skripkin <paskripkin@...il.com>
> Sent: 24 August 2021 08:28
> 
> _rtw_read32 function can fail in case of usb transfer failure. But
> previous function prototype wasn't designed to return an error to
> caller. It can cause a lot uninit value bugs all across the driver code,
> since rtw_read32() returns local stack variable to caller.
> 
> Fix it by changing the prototype of this function. Now it returns an
> int: 0 on success, negative error value on failure and callers should pass
> the pointer to storage location for register value.

Pretty horrid API interface.
Functions like readl() - which can fail just return ~0u and let
the caller worry about whether that causes serious grief.

You could make all the read functions return __u64 and return ~0ull
on error.
Testing for (value & 1ull << 63) will be reasonable even on 32bit.

...
> -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.

	David

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