linux-kernel - Re: [PATCH] power: supply: sysfs: prevent endless uevent loop with CONFIG_POWER_SUPPLY

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Date:   Thu, 18 Apr 2019 00:37:08 +0200
From:   Sebastian Reichel <sre@...nel.org>
To:     Andrey Smirnov <andrew.smirnov@...il.com>
Cc:     Chris Healy <cphealy@...il.com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] power: supply: sysfs: prevent endless uevent loop with
 CONFIG_POWER_SUPPLY_DEBUG

Hi,

On Fri, Apr 05, 2019 at 12:30:20AM -0700, Andrey Smirnov wrote:
> Fix a similar endless event loop as was done in commit 8dcf32175b4e
> ("i2c: prevent endless uevent loop with CONFIG_I2C_DEBUG_CORE"):
> 
>   The culprit is the dev_dbg printk in the i2c uevent handler. If
>   this is activated (for instance by CONFIG_I2C_DEBUG_CORE) it results
>   in an endless loop with systemd-journald.
> 
>   This happens if user-space scans the system log and reads the uevent
>   file to get information about a newly created device, which seems
>   fair use to me. Unfortunately reading the "uevent" file uses the
>   same function that runs for creating the uevent for a new device,
>   generating the next syslog entry
> 
> Both CONFIG_I2C_DEBUG_CORE and CONFIG_POWER_SUPPLY_DEBUG were reported
> in https://bugs.freedesktop.org/show_bug.cgi?id=76886 but only former
> seems to have been fixed. Change debug prints to use pr_debug insted
> to resolve the issue.
> 
> Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
> Cc: Chris Healy <cphealy@...il.com>
> Cc: Sebastian Reichel <sre@...nel.org>
> Cc: linux-pm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---

I think we should just drop these debug messages, just like I2C did.
They don't offer any useful information considering the info is already
exposed to userspace via the uevent.

-- Sebastian

>  drivers/power/supply/power_supply_sysfs.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/power/supply/power_supply_sysfs.c b/drivers/power/supply/power_supply_sysfs.c
> index dce24f596160..5e91946731fd 100644
> --- a/drivers/power/supply/power_supply_sysfs.c
> +++ b/drivers/power/supply/power_supply_sysfs.c
> @@ -383,14 +383,14 @@ int power_supply_uevent(struct device *dev, struct kobj_uevent_env *env)
>  	char *prop_buf;
>  	char *attrname;
>  
> -	dev_dbg(dev, "uevent\n");
> +	pr_debug("%s: uevent\n", dev_name(dev));
>  
>  	if (!psy || !psy->desc) {
>  		dev_dbg(dev, "No power supply yet\n");
>  		return ret;
>  	}
>  
> -	dev_dbg(dev, "POWER_SUPPLY_NAME=%s\n", psy->desc->name);
> +	pr_debug("%s: POWER_SUPPLY_NAME=%s\n", dev_name(dev), psy->desc->name);
>  
>  	ret = add_uevent_var(env, "POWER_SUPPLY_NAME=%s", psy->desc->name);
>  	if (ret)
> @@ -427,7 +427,8 @@ int power_supply_uevent(struct device *dev, struct kobj_uevent_env *env)
>  			goto out;
>  		}
>  
> -		dev_dbg(dev, "prop %s=%s\n", attrname, prop_buf);
> +		pr_debug("%s: prop %s=%s\n", dev_name(dev), attrname,
> +			 prop_buf);
>  
>  		ret = add_uevent_var(env, "POWER_SUPPLY_%s=%s", attrname, prop_buf);
>  		kfree(attrname);
> -- 
> 2.20.1
> 

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