linux-kernel - Re: [linux-pm] [PATCH v4] cpuidle: Add a sysfs entry to disable specific C state for debug purpose.

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Message-Id: <20120316152323.3c629e5c.akpm@linux-foundation.org>
Date:	Fri, 16 Mar 2012 15:23:23 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	shuox.liu@...el.com
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Yanmin Zhang <yanmin_zhang@...ux.intel.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	"Brown, Len" <len.brown@...el.com>, Ingo Molnar <mingo@...e.hu>,
	Greg KH <gregkh@...uxfoundation.org>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	"H. Peter Anvin" <hpa@...or.com>, andi.kleen@...el.com,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-pm@...ts.linux-foundation.org" 
	<linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] [PATCH v4] cpuidle: Add a sysfs entry to disable
 specific C state for debug purpose.

On Wed, 14 Mar 2012 11:24:40 +0800
ShuoX Liu <shuox.liu@...el.com> wrote:

> From: ShuoX Liu <shuox.liu@...el.com>
> 
> Some C states of new CPU might be not good. One reason is BIOS might configure
> them incorrectly. To help developers root cause it quickly, the patch adds a
> new sysfs entry, so developers could disable specific C state manually.
> 
> In addition, C state might have much impact on performance tuning, as it takes
> much time to enter/exit C states, which might delay interrupt processing. With
> the new debug option, developers could check if a deep C state could  impact
> performance and how much impact it could cause.
> 
> ...
>
> +#define define_store_state_function(_name) \
> +static ssize_t store_state_##_name(struct cpuidle_state *state, \
> +		const char *buf, size_t size) \
> +{ \
> +	long value; \
> +	if (!capable(CAP_SYS_ADMIN)) \
> +		return -EPERM; \
> +	kstrtol(buf, 0, &value); \
> +	if (value) \
> +		state->disable = 1; \
> +	else \
> +		state->disable = 0; \
> +	return size; \
> +}

drivers/cpuidle/sysfs.c: In function 'store_state_disable':
drivers/cpuidle/sysfs.c:274: warning: ignoring return value of 'kstrtol', declared with attribute warn_unused_result

The check is there for a reason - the kernel shouldn't silently accept
random garbage inputs.

--- a/drivers/cpuidle/sysfs.c~cpuidle-add-a-sysfs-entry-to-disable-specific-c-state-for-debug-purpose-fix
+++ a/drivers/cpuidle/sysfs.c
@@ -238,9 +238,12 @@ static ssize_t store_state_##_name(struc
 		const char *buf, size_t size) \
 { \
 	long value; \
+	int err; \
 	if (!capable(CAP_SYS_ADMIN)) \
 		return -EPERM; \
-	kstrtol(buf, 0, &value); \
+	err = kstrtol(buf, 0, &value); \
+	if (err) \
+		return err; \
 	if (value) \
 		state->disable = 1; \
 	else \
_

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