[PATCH] driver core: Prevent overriding async driver of a device before it probe

[Mark-PK Tsai <mark-pk.tsai@mediatek.com>]

When there are 2 matched drivers for a device using
async probe mechanism, the dev->p->async_driver might
be overridden by the last attached driver.
So just skip the later one if the previous matched driver
was not handled by async thread yet.

Below is my use case which having this problem.

Make both driver mmcblk and mmc_test allow async probe,
the dev->p->async_driver will be overridden by the later driver
mmc_test and bind to the device then claim it for testing.
When it happen, mmcblk will never do probe again.

Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
---
 drivers/base/dd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index f47cab21430f..f0bd779a4696 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -1085,6 +1085,7 @@ static void __driver_attach_async_helper(void *_dev, async_cookie_t cookie)
 
 	__device_driver_lock(dev, dev->parent);
 	drv = dev->p->async_driver;
+	dev->p->async_driver = NULL;
 	ret = driver_probe_device(drv, dev);
 	__device_driver_unlock(dev, dev->parent);
 
@@ -1131,7 +1132,7 @@ static int __driver_attach(struct device *dev, void *data)
 		 */
 		dev_dbg(dev, "probing driver %s asynchronously\n", drv->name);
 		device_lock(dev);
-		if (!dev->driver) {
+		if (!dev->driver && !dev->p->async_driver) {
 			get_device(dev);
 			dev->p->async_driver = drv;
 			async_schedule_dev(__driver_attach_async_helper, dev);
-- 
2.18.0