linux-kernel - usb: storage: suspicious code

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Date:   Tue, 14 Feb 2017 23:06:52 -0600
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     stern@...land.harvard.edu, gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, usb-storage@...ts.one-eyed-alien.net,
        linux-kernel@...r.kernel.org,
        Peter Senna Tschudi <peter.senna@...il.com>,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Subject: usb: storage: suspicious code

Hello,

I ran into the following piece of code at drivers/usb/storage/jumpshot.c:305 (linux-next), and it seems a little bit suspicious:

// read the result.  apparently the bulk write can complete
// before the jumpshot drive is finished writing.  so we loop
// here until we get a good return code
waitcount = 0;
do {
	result = jumpshot_get_status(us);
	if (result != USB_STOR_TRANSPORT_GOOD) {
        	// I have not experimented to find the smallest value.
		//
		msleep(50);
	}
	} while ((result != USB_STOR_TRANSPORT_GOOD) && (waitcount < 10));

	if (result != USB_STOR_TRANSPORT_GOOD)
        	usb_stor_dbg(us, "Gah!  Waitcount = 10.  Bad write!?\n");

Variable 'waitcount' is never updated inside the do-while loop. So, either it isn't needed at all or line 316 should be modified (++waitcount < 10)

In case 'waitcount' isn't needed, lines 318 and 319 should be removed.

Can someone help me to clarify this so I can write a patch to fix this code?

Thank you
--
Gustavo A. R. Silva