On Thu, 26 Aug 2021 08:51:23 +0000
David Laight [off-list ref] wrote:

From: Pavel Skripkin <redacted>

quoted

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.

I am not the best at API related questions, so can you, please,
explain why your approach is better? 

As I can see, most of the drivers in usb/ directory use smth like this
interface for private reading funcions. We anyway creating tmp variable
(but 64 bit _always_) and checking for mistery error, which we cannot
pass up to callers.

Sorry, if it's _too_ dumb question, but I really can't get your
point....



 

...

quoted

-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




With regards,
Pavel Skripkin