Re: [PATCH] i2c: Prevent endless uevent loop with dev_dbg

[Wolfram Sang]

On Wed, Mar 23, 2016 at 04:50:47PM +0100, Jan Glauber wrote:
> 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.

Thanks for pointing out this problem. I think this debug can go. I also
think the function can be cleaned up some more. Can you test this patch?

Thanks,

   Wolfram

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 0f2f8484e8ec1f..e584d88ee337f6 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -525,22 +525,16 @@ static int i2c_device_match(struct device *dev, struct device_driver *drv)
 	return 0;
 }
 
-
-/* uevent helps with hotplug: modprobe -q $(MODALIAS) */
 static int i2c_device_uevent(struct device *dev, struct kobj_uevent_env *env)
 {
-	struct i2c_client	*client = to_i2c_client(dev);
+	struct i2c_client *client = to_i2c_client(dev);
 	int rc;
 
 	rc = acpi_device_uevent_modalias(dev, env);
 	if (rc != -ENODEV)
 		return rc;
 
-	if (add_uevent_var(env, "MODALIAS=%s%s",
-			   I2C_MODULE_PREFIX, client->name))
-		return -ENOMEM;
-	dev_dbg(dev, "uevent\n");
-	return 0;
+	return add_uevent_var(env, "MODALIAS=%s%s", I2C_MODULE_PREFIX, client->name);
 }
 
 /* i2c bus recovery routines */

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