linux-kernel - [PATCH-next v2 1/2] driver core: introduce get_device_unless

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Date:   Sat, 28 Jan 2023 17:41:45 +0800
From:   Zhong Jinghua <zhongjinghua@...wei.com>
To:     <gregkh@...uxfoundation.org>, <jejb@...ux.ibm.com>,
        <martin.petersen@...cle.com>, <hare@...e.de>, <bvanassche@....org>,
        <emilne@...hat.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-scsi@...r.kernel.org>,
        <zhongjinghua@...wei.com>, <yi.zhang@...wei.com>,
        <yukuai3@...wei.com>
Subject: [PATCH-next v2 1/2] driver core: introduce get_device_unless_zero()

When the dev reference count is 0, calling get_device will go from 0 to 1,
which will cause errors in some place of the kernel. So introduce a
get_devcie_unless_zero method that returns NULL when the dev reference
count is 0.

Signed-off-by: Zhong Jinghua <zhongjinghua@...wei.com>
---
 drivers/base/core.c    | 8 ++++++++
 include/linux/device.h | 1 +
 2 files changed, 9 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index d02501933467..6f17a93a3443 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -3613,6 +3613,14 @@ struct device *get_device(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(get_device);
 
+struct device __must_check *get_device_unless_zero(struct device *dev)
+{
+	if (!dev || !kobject_get_unless_zero(&dev->kobj))
+		return NULL;
+	return dev;
+}
+EXPORT_SYMBOL_GPL(get_device_unless_zero);
+
 /**
  * put_device - decrement reference count.
  * @dev: device in question.
diff --git a/include/linux/device.h b/include/linux/device.h
index 424b55df0272..c63bac6d51c8 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1069,6 +1069,7 @@ extern int (*platform_notify_remove)(struct device *dev);
  *
  */
 struct device *get_device(struct device *dev);
+struct device __must_check *get_device_unless_zero(struct device *dev);
 void put_device(struct device *dev);
 bool kill_device(struct device *dev);
 
-- 
2.31.1