From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793035895; b=JA7KziOMqKNMWwRwhJbvcUiSuNnpidpgfVEMRFjNegjc/afmfSEAKvDX6Zf+KogjPfPd NEXFS58jWX4ZTBW1Fjh07duDUlkjggWz4r8UuG04MNDAVaUFkee4WngISC5TT/3K/xHTT RpofNSEbpZRXsJR5DNeKlpfW61B+bNt9XA95TEsvlygWfTDQ0cmsClfpte89GrzvESy1d JN6u8wIzSBvkpObYk27Oxm9j3dOmEqAEWz724Bc9mhN3sQXTHyW/fw2VXV48VZQskyRf9 vjZHqep9e4XhE47HV6W5clUf4EM4dafEJFyxvQjh1MnZt1REQ9pn12T/f3ML4J8fRoA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793035895; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=mjT/jJuFM6XBK5jXoyA5s/eNOp2DUiiIPlqtvzyid0Q=; b=RLiURNujKWWu5f6O+BLwzKCEUeq3HJVsjcQMjHIG4oBIRFmHlkGd/yRtdfU7Fjvd/PuW zggPXYv1ntlY2YRie0NqwKJ1mQHJxIQCBvR+mHyVvURNkU9CkNasN5HlaS5POgU9/Fd9i eSzaaiE4K4g6kOYKt7OKP9L5rNCl+JEWA4rGesHlhC0ysKaeHF3R651ILxueIYQe7hAgo vl/FD+3Wrw0gx3Vk5Fc0/YBnKB+qU2IVQrNPUbAeo0AujmF1oh5xHKCS4wr1txx8io8vd R9zlxYu2+gF1XS69WS6w2Zg59ea2gTt+1WIyRACNYCXnhbOEEQ356RhmYYnB7PMfkjA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=GL8Z2bVj; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E2763606A31A; Mon, 26 Oct 2026 17:31:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=GL8Z2bVj Received: by smtp.kernel.org (Postfix) with ESMTPSA id 778061F01825; Mon, 26 Oct 2026 17:31:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793035894; bh=mjT/jJuFM6XBK5jXoyA5s/eNOp2DUiiIPlqtvzyid0Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=GL8Z2bVjh1iQjwgmKrgs50oO9s/5XVCtHvyU0etT5FZlYyrrdGOZ1Ms+v9BInuK2a N+yISQv/k95xO8+gyX8HkagUvYUwNKWFtOZfYTTqv2aarHNF3JRhG+aIIKN6SNbc8U G4KnxxoYktMtSpcrLGtTYAatssL+utymuiMUVMvMlS/MSCmDTbHyXsD97pmIy80y9k B3IUjO7egnN9ohbnePwNQvqcdStVVM1HGuVWPQLDnXnWhRFDTYyk4mWRNxRX/GDaVE OtmXq/lOhBkKxy9YnyqQuViw99n9XbTQzRf4f9kvYcajAQNWqXi+z8FB0n1Zx63zBB 2HRlp86THJUqQ== Date: Mon, 26 Oct 2026 17:31:29 +0000 From: Lee Jones To: David Laight Cc: Pavel Machek , Dmitry Antipov , Jacek Anaszewski , Bryan Wu , Kyungmin Park , linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 14/21] leds: flash: Avoid divide-by-zero in led_clamp_align() Message-ID: <20261026173129.GF2195460@google.com> References: <20261021123406.3163547-1-lee@kernel.org> <20261021123406.3163547-15-lee@kernel.org> <20261022220006.6e066670@pumpkin> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261022220006.6e066670@pumpkin> On Thu, 22 Oct 2026, David Laight wrote: > On Wed, 21 Oct 2026 12:32:23 +0000 > Lee Jones wrote: > > > If a flash LED driver leaves a setting's step size as zero, writing to > > the corresponding sysfs attribute invokes led_clamp_align() and triggers > > an integer division by zero when aligning the offset to s->step. > > > > Clamp s->val to [s->min, s->max] and return early when s->step is zero. > > > > Fixes: 7aea8389a77a ("leds: Add LED Flash class extension to the LED subsystem") > > Closes: https://sashiko.dev/#/bug/linux-9d06d7fe-310b-4aee-8b16-0fb49550c287 > > Cc: stable@vger.kernel.org > > Signed-off-by: Lee Jones > > --- > > drivers/leds/led-class-flash.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/drivers/leds/led-class-flash.c b/drivers/leds/led-class-flash.c > > index 181dfd49c6ad..16b3b6b9365b 100644 > > --- a/drivers/leds/led-class-flash.c > > +++ b/drivers/leds/led-class-flash.c > > @@ -375,6 +375,11 @@ static void led_clamp_align(struct led_flash_setting *s) > > { > > u32 v, offset; > > > > + if (!s->step) { > > + s->val = clamp(s->val, s->min, s->max); > > + return; > > + } > > Why not just: > u32 step = s->step ?: 1; > and then use step instead of s->step. I can see where you're coming from, but I don't think this is better. With `step = 1`, the reader has to mentally trace `1 / 2 == 0` and `1 * (offset / 1) == offset` to see that it reduces to a plain clamp and the CPU still executes a redundant integer division. IMHO, simple, easy-to-read, maintainable code wins out over clever code. > > + > > v = s->val + s->step / 2; > > v = clamp(v, s->min, s->max); > > offset = v - s->min; > -- Lee Jones