[PATCH] i2c: Prevent endless uevent loop with dev_dbg

From: Jan Glauber
Date: Wed Mar 23 2016 - 11:51:31 EST

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:

Signed-off-by: Jan Glauber <jglauber@xxxxxxxxxx>
drivers/i2c/i2c-core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 0f2f848..84165d9 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -539,7 +539,7 @@ static int i2c_device_uevent(struct device *dev, struct kobj_uevent_env *env)
if (add_uevent_var(env, "MODALIAS=%s%s",
I2C_MODULE_PREFIX, client->name))
return -ENOMEM;
- dev_dbg(dev, "uevent\n");
+ pr_debug("uevent: device: %s\n", dev_name(dev));
return 0;