[patch 2.6.27-rc7] i2c: guard against oopses from bad init sequences

[David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>]

From: David Brownell <dbrownell-Rn4VEauK+AKRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>

Guard I2C against oopsing because of init sequence problems, by
verifying that i2c_init() has been called before calling any
routines that rely on that initialization.  This specific test
just requires that bus_register(&i2c_bus_type) was called.

Examples of this kind of oopsing come from subystems and drivers
which register I2C drivers in their subsys_initcall code but
which are statically linked before I2C by drivers/Makefile.

Signed-off-by: David Brownell <dbrownell-Rn4VEauK+AKRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>
---
Alternatively have postcore_initcall(i2c_init), which may
be better ... the initcall levels are pretty limited, and
in these cases the "subsystem" of interest builds on I2C
and needs to work before device_initcall.  Having I2C use
subsys_initcall kind of forces things into fs_initcall.

I'd encourage the anti-oopsing paranoia in any case, even
if i2c switches to postcore_initcall (or earlier).

 drivers/i2c/i2c-core.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -443,6 +443,12 @@ static int i2c_register_adapter(struct i
 
 	mutex_lock(&core_lock);
 
+	/* can't register until after driver model init */
+	if (WARN_ON(!i2c_bus_type.p)) {
+		res = -ENOENT;
+		goto out_list;
+	}
+
 	/* Add the adapter to the driver core.
 	 * If the parent pointer is not set up,
 	 * we add this adapter to the host bus.
@@ -696,6 +702,10 @@ int i2c_register_driver(struct module *o
 {
 	int res;
 
+	/* can't register until after driver model init */
+	if (WARN_ON(!i2c_bus_type.p))
+		return -ENOENT;
+
 	/* new style driver methods can't mix with legacy ones */
 	if (is_newstyle_driver(driver)) {
 		if (driver->attach_adapter || driver->detach_adapter

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