linux-kernel - Re: [PATCH] i2c: prevent endless uevent loop with CONFIG_I2C_DEBUG

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Message-ID: <20160330122300.GB9329@katana>
Date:	Wed, 30 Mar 2016 14:23:01 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	linux-i2c@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Jan Glauber <jglauber@...ium.com>,
	Alexander Sverdlin <alexander.sverdlin@...ia.com>
Subject: Re: [PATCH] i2c: prevent endless uevent loop with
 CONFIG_I2C_DEBUG_CORE

On Wed, Mar 23, 2016 at 08:47:02PM +0100, Wolfram Sang wrote:
> Jan reported this:
> ===
> After enabling CONFIG_I2C_DEBUG_CORE my system was broken
> (no network, console login not possible). System log was
> flooded with the this message:
> 
>  ...
> [  608.052077] rtc-ds1307 0-0068: uevent
> [  608.052500] rtc-ds1307 0-0068: uevent
> [  608.052925] rtc-ds1307 0-0068: uevent
>  ...
> 
> 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.
> 
> Ideally user-space would implement a recursion detection and
> after reading the same device file for the 1000th time call it a
> day, but nevertheless I think we should avoid this problem by
> removing the debug print completly or using another print variant.
> 
> The same problem seems to be reported here:
> https://bugs.freedesktop.org/show_bug.cgi?id=76886
> ===
> 
> His patch converted the message to pr_debug, but I think the debug can
> simply go. We have other means to see code paths these days. This
> enables us to clean up the function some more while we are here.
> 
> Reported-by: Jan Glauber <jglauber@...ium.com>
> Signed-off-by: Wolfram Sang <wsa@...-dreams.de>
> Acked-by: Alexander Sverdlin <alexander.sverdlin@...ia.com>
> Tested-by: Jan Glauber <jglauber@...ium.com>

Applied to for-current, thanks!


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