driver core: use READ_ONCE() for dev->driver in dev_has_sync_state()

dev_has_sync_state() reads dev->driver twice without holding
device_lock() -- once for the NULL check and once to dereference
->sync_state. Some callers only hold device_links_write_lock, which
doesn't prevent a concurrent unbind from clearing dev->driver via
device_unbind_cleanup().

Fix it by reading dev->driver exactly once with READ_ONCE(), pairing
with the WRITE_ONCE() in device_set_driver().

Link: https://lore.kernel.org/driver-core/DHW8QPU1VU1F.3P6PH69HLFBYC@kernel.org/
Fixes: ac338acf514e ("driver core: Add dev_has_sync_state()")
Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Saravana Kannan <saravanak@kernel.org>
Link: https://patch.msgid.link/20260418162221.1121873-1-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

diff --git a/include/linux/device.h b/include/linux/device.h
index 3bf86d2f95448524bf07daceac2c15bea29f98cc..56a96e41d2c90570772fba05768e2cf00f643dc9 100644 (file)
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1063,9 +1063,12 @@ static inline void device_lock_assert(struct device *dev)
 
 static inline bool dev_has_sync_state(struct device *dev)
 {
+       struct device_driver *drv;
+
        if (!dev)
                return false;
-       if (dev->driver && dev->driver->sync_state)
+       drv = READ_ONCE(dev->driver);
+       if (drv && drv->sync_state)
                return true;
        if (dev->bus && dev->bus->sync_state)
                return true;