i2c: Limit core locking to the necessary sections

The i2c-core code tends to hold the core lock for longer than it
should. Limit locking to the necessary sections for both performance
and clarity. This is also a requirement to support I2C multiplexers in
the future.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Tested-by: Rodolfo Giometti <giometti@linux.it>
Cc: David Brownell <dbrownell@users.sourceforge.net>

1 files changed, 28 insertions, 23 deletions

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index b1fd00d9a5c..a2f1cd3766f 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -38,6 +38,9 @@
 #include "i2c-core.h"
 
 
+/* core_lock protects i2c_adapter_idr, and guarantees
+   that device detection, deletion of detected devices, and attach_adapter
+   and detach_adapter calls are serialized */
 static DEFINE_MUTEX(core_lock);
 static DEFINE_IDR(i2c_adapter_idr);
 
@@ -418,13 +421,13 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
         int res = 0, dummy;
 
         /* Can't register until after driver model init */
-        if (unlikely(WARN_ON(!i2c_bus_type.p)))
-                return -EAGAIN;
+        if (unlikely(WARN_ON(!i2c_bus_type.p))) {
+                res = -EAGAIN;
+                goto out_list;
+        }
 
         mutex_init(&adap->bus_lock);
 
-        mutex_lock(&core_lock);
-
         /* Set default timeout to 1 second if not already set */
         if (adap->timeout == 0)
                 adap->timeout = HZ;
@@ -443,16 +446,18 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
                 i2c_scan_static_board_info(adap);
 
         /* Notify drivers */
+        mutex_lock(&core_lock);
         dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
                                  i2c_do_add_adapter);
-
-out_unlock:
         mutex_unlock(&core_lock);
-        return res;
+
+        return 0;
 
 out_list:
+        mutex_lock(&core_lock);
         idr_remove(&i2c_adapter_idr, adap->nr);
-        goto out_unlock;
+        mutex_unlock(&core_lock);
+        return res;
 }
 
 /**
@@ -590,22 +595,25 @@ static int __unregister_client(struct device *dev, void *dummy)
 int i2c_del_adapter(struct i2c_adapter *adap)
 {
         int res = 0;
-
-        mutex_lock(&core_lock);
+        struct i2c_adapter *found;
 
         /* First make sure that this adapter was ever added */
-        if (idr_find(&i2c_adapter_idr, adap->nr) != adap) {
+        mutex_lock(&core_lock);
+        found = idr_find(&i2c_adapter_idr, adap->nr);
+        mutex_unlock(&core_lock);
+        if (found != adap) {
                 pr_debug("i2c-core: attempting to delete unregistered "
                          "adapter [%s]\n", adap->name);
-                res = -EINVAL;
-                goto out_unlock;
+                return -EINVAL;
         }
 
         /* Tell drivers about this removal */
+        mutex_lock(&core_lock);
         res = bus_for_each_drv(&i2c_bus_type, NULL, adap,
                                i2c_do_del_adapter);
+        mutex_unlock(&core_lock);
         if (res)
-                goto out_unlock;
+                return res;
 
         /* Detach any active clients. This can't fail, thus we do not
            checking the returned value. */
@@ -619,7 +627,9 @@ int i2c_del_adapter(struct i2c_adapter *adap)
         wait_for_completion(&adap->dev_released);
 
         /* free bus id */
+        mutex_lock(&core_lock);
         idr_remove(&i2c_adapter_idr, adap->nr);
+        mutex_unlock(&core_lock);
 
         dev_dbg(&adap->dev, "adapter [%s] unregistered\n", adap->name);
 
@@ -627,9 +637,7 @@ int i2c_del_adapter(struct i2c_adapter *adap)
            added again */
         memset(&adap->dev, 0, sizeof(adap->dev));
 
- out_unlock:
-        mutex_unlock(&core_lock);
-        return res;
+        return 0;
 }
 EXPORT_SYMBOL(i2c_del_adapter);
 
@@ -674,16 +682,15 @@ int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
         if (res)
                 return res;
 
-        mutex_lock(&core_lock);
-
         pr_debug("i2c-core: driver [%s] registered\n", driver->driver.name);
 
         INIT_LIST_HEAD(&driver->clients);
         /* Walk the adapters that are already present */
+        mutex_lock(&core_lock);
         class_for_each_device(&i2c_adapter_class, NULL, driver,
                               __attach_adapter);
-
         mutex_unlock(&core_lock);
+
         return 0;
 }
 EXPORT_SYMBOL(i2c_register_driver);
@@ -721,14 +728,12 @@ static int __detach_adapter(struct device *dev, void *data)
 void i2c_del_driver(struct i2c_driver *driver)
 {
         mutex_lock(&core_lock);
-
         class_for_each_device(&i2c_adapter_class, NULL, driver,
                               __detach_adapter);
+        mutex_unlock(&core_lock);
 
         driver_unregister(&driver->driver);
         pr_debug("i2c-core: driver [%s] unregistered\n", driver->driver.name);
-
-        mutex_unlock(&core_lock);
 }
 EXPORT_SYMBOL(i2c_del_driver);