Re: [i2c: i2c-core] f3eab42515: WARNING: CPU: 0 PID: 1 at drivers/i2c/i2c-core.c:1930 i2c_register_driver()

[Sudip Mukherjee <sudipm.mukherjee@gmail.com>]

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On Monday 07 March 2016 06:19 PM, kernel test robot wrote:
> Greetings,
>
> 0day kernel testing robot got the below dmesg and the first bad commit is
>
> https://github.com/0day-ci/linux Sudip-Mukherjee/i2c-i2c-core-do-not-use-bus-internal-data/20160307-195104
>
> commit f3eab4251515a492aa38e515d9a2322c535ce358
> Author:     Sudip Mukherjee <sudipm.mukherjee@gmail.com>
> AuthorDate: Mon Mar 7 17:19:17 2016 +0530
> Commit:     0day robot <fengguang.wu@intel.com>
> CommitDate: Mon Mar 7 19:51:06 2016 +0800
>
>      i2c: i2c-core: do not use bus internal data
>
>      The variable p is a data structure which is used by the driver core
>      internally and it is not expected that busses will be directly accessing
>      these driver core internal only data.
>
>      Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>

The warnings and stacktrace are expected as there was a WARN_ON() in it. 
But can you please check if the attached patch fixes the BUG: and the 
null pointer dereference. The patch will apply on top of my previous 
patch (i2c: i2c-core: do not use bus internal data).

regards
sudip




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diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 2f31fb5..80235db 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -75,6 +75,12 @@ static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver);
 static struct static_key i2c_trace_msg = STATIC_KEY_INIT_FALSE;
 static bool is_registered;
 
+bool is_i2c_registered(void)
+{
+	return is_registered;
+}
+EXPORT_SYMBOL(is_i2c_registered);
+
 void i2c_transfer_trace_reg(void)
 {
 	static_key_slow_inc(&i2c_trace_msg);
diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
index 0b1108d..1939827 100644
--- a/drivers/i2c/i2c-dev.c
+++ b/drivers/i2c/i2c-dev.c
@@ -620,6 +620,9 @@ static int __init i2c_dev_init(void)
 
 	printk(KERN_INFO "i2c /dev entries driver\n");
 
+	if (!is_i2c_registered())
+		return -EAGAIN;
+
 	res = register_chrdev(I2C_MAJOR, "i2c", &i2cdev_fops);
 	if (res)
 		goto out;
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 200cf13b..24b42ff 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -36,6 +36,7 @@
 
 extern struct bus_type i2c_bus_type;
 extern struct device_type i2c_adapter_type;
+bool is_i2c_registered(void);
 
 /* --- General options ------------------------------------------------	*/