linux-kernel - RE: [PATCH] staging: wlan-ng: Avoid bitwise vs logical OR warning in hfa384x_usb

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Date:   Wed, 20 Oct 2021 08:14:42 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Nathan Chancellor' <nathan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Nick Desaulniers <ndesaulniers@...gle.com>,
        "linux-staging@...ts.linux.dev" <linux-staging@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>
Subject: RE: [PATCH] staging: wlan-ng: Avoid bitwise vs logical OR warning in
 hfa384x_usb_throttlefn()

From: Nathan Chancellor
> Sent: 14 October 2021 22:57
> 
> A new warning in clang points out a place in this file where a bitwise
> OR is being used with boolean expressions:
> 
> In file included from drivers/staging/wlan-ng/prism2usb.c:2:
> drivers/staging/wlan-ng/hfa384x_usb.c:3787:7: warning: use of bitwise '|' with boolean operands [-
> Wbitwise-instead-of-logical]
>             ((test_and_clear_bit(THROTTLE_RX, &hw->usb_flags) &&
>             ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/staging/wlan-ng/hfa384x_usb.c:3787:7: note: cast one or both operands to int to silence this
> warning
> 1 warning generated.
> 
> The comment explains that short circuiting here is undesirable, as the
> calls to test_and_{clear,set}_bit() need to happen for both sides of the
> expression.
> 
> Clang's suggestion would work to silence the warning but the readability
> of the expression would suffer even more. To clean up the warning and
> make the block more readable, use a variable for each side of the
> bitwise expression.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1478
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  drivers/staging/wlan-ng/hfa384x_usb.c | 22 +++++++++++-----------
>  1 file changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/staging/wlan-ng/hfa384x_usb.c b/drivers/staging/wlan-ng/hfa384x_usb.c
> index 59aa84d1837d..938e11a1a0b6 100644
> --- a/drivers/staging/wlan-ng/hfa384x_usb.c
> +++ b/drivers/staging/wlan-ng/hfa384x_usb.c
> @@ -3778,18 +3778,18 @@ static void hfa384x_usb_throttlefn(struct timer_list *t)
> 
>  	spin_lock_irqsave(&hw->ctlxq.lock, flags);
> 
> -	/*
> -	 * We need to check BOTH the RX and the TX throttle controls,
> -	 * so we use the bitwise OR instead of the logical OR.
> -	 */
>  	pr_debug("flags=0x%lx\n", hw->usb_flags);
> -	if (!hw->wlandev->hwremoved &&
> -	    ((test_and_clear_bit(THROTTLE_RX, &hw->usb_flags) &&
> -	      !test_and_set_bit(WORK_RX_RESUME, &hw->usb_flags)) |
> -	     (test_and_clear_bit(THROTTLE_TX, &hw->usb_flags) &&
> -	      !test_and_set_bit(WORK_TX_RESUME, &hw->usb_flags))
> -	    )) {
> -		schedule_work(&hw->usb_work);
> +	if (!hw->wlandev->hwremoved) {
> +		bool rx_throttle = test_and_clear_bit(THROTTLE_RX, &hw->usb_flags) &&
> +				   !test_and_set_bit(WORK_RX_RESUME, &hw->usb_flags);
> +		bool tx_throttle = test_and_clear_bit(THROTTLE_TX, &hw->usb_flags) &&
> +				   !test_and_set_bit(WORK_TX_RESUME, &hw->usb_flags);
> +		/*
> +		 * We need to check BOTH the RX and the TX throttle controls,
> +		 * so we use the bitwise OR instead of the logical OR.
> +		 */
> +		if (rx_throttle | tx_throttle)
> +			schedule_work(&hw->usb_work);

Why not the slightly simpler:
		bool throttle = test_and_clear_bit(THROTTLE_RX, &hw->usb_flags) &&
				   !test_and_set_bit(WORK_RX_RESUME, &hw->usb_flags);
		throttle |= test_and_clear_bit(THROTTLE_TX, &hw->usb_flags) &&
				   !test_and_set_bit(WORK_TX_RESUME, &hw->usb_flags);
		if (throttle)
			schedule_work(&hw->usb_work);
or with s/throttle/throttle_silly_compiler_warning/ :-)

	David

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