linux-kernel - Re: [PATCH] rtc: twl: optimize IRQ bit access

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 27 Jan 2012 16:38:40 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Venu Byravarasu <vbyravarasu@...dia.com>
Cc:	a.zummo@...ertech.it, rtc-linux@...glegroups.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: twl: optimize IRQ bit access

On Thu, 19 Jan 2012 17:22:22 +0530
Venu Byravarasu <vbyravarasu@...dia.com> wrote:

> From: Venu Byravarasu <vbyravarasu@...dia.com>
> 
> As TWL RTC driver is having a cached copy of enabled RTC interrupt bits
> in variable rtc_irq_bits, that can be checked before really setting
> or masking any of the interrupt bits.
> 
> ...
>
> --- a/drivers/rtc/rtc-twl.c
> +++ b/drivers/rtc/rtc-twl.c
> @@ -176,6 +176,10 @@ static int set_rtc_irq_bit(unsigned char bit)
>  	unsigned char val;
>  	int ret;
>  
> +	/* if the bit is set, return from here */
> +	if (rtc_irq_bits & bit)
> +		return 0;
> +
>  	val = rtc_irq_bits | bit;
>  	val &= ~BIT_RTC_INTERRUPTS_REG_EVERY_M;
>  	ret = twl_rtc_write_u8(val, REG_RTC_INTERRUPTS_REG);
> @@ -193,6 +197,10 @@ static int mask_rtc_irq_bit(unsigned char bit)
>  	unsigned char val;
>  	int ret;
>  
> +	/* if the bit is clear, return from here */
> +	if (!(rtc_irq_bits & bit))
> +		return 0;
> +
>  	val = rtc_irq_bits & ~bit;
>  	ret = twl_rtc_write_u8(val, REG_RTC_INTERRUPTS_REG);
>  	if (ret == 0)

Are these functions called frequently enough to make this optimisation
significant?

I can see no locking protecting rtc_irq_bits from concurrent updaters. 
Is this code as racy as it appears?


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/