i2c: core: Lock address during client device instantiation

Krzysztof reported an issue [0] which is caused by parallel attempts to
instantiate the same I2C client device. This can happen if driver
supports auto-detection, but certain devices are also instantiated
explicitly.
The original change isn't actually wrong, it just revealed that I2C core
isn't prepared yet to handle this scenario.
Calls to i2c_new_client_device() can be nested, therefore we can't use a
simple mutex here. Parallel instantiation of devices at different addresses
is ok, so we just have to prevent parallel instantiation at the same address.
We can use a bitmap with one bit per 7-bit I2C client address, and atomic
bit operations to set/check/clear bits.
Now a parallel attempt to instantiate a device at the same address will
result in -EBUSY being returned, avoiding the "sysfs: cannot create duplicate
filename" splash.

Note: This patch version includes small cosmetic changes to the Tested-by
      version, only functional change is that address locking is supported
      for slave addresses too.

[0] https://lore.kernel.org/linux-i2c/9479fe4e-eb0c-407e-84c0-bd60c15baf74@ans.pl/T/#m12706546e8e2414d8f1a0dc61c53393f731685cc

Fixes: caba40ec3531 ("eeprom: at24: Probe for DDR3 thermal sensor in the SPD case")
Cc: stable@vger.kernel.org
Tested-by: Krzysztof Piotr Oledzki <ole@ans.pl>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 7eedd0c662da..8d79440cd8ce 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -761,6 +761,9 @@ struct i2c_adapter {
 	struct regulator *bus_regulator;
 
 	struct dentry *debugfs;
+
+	/* 7bit address space */
+	DECLARE_BITMAP(addrs_in_instantiation, 1 << 7);
 };
 #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)