Re: [PATCH-next v2 1/2] driver core: introduce get_device_unless_zero()

From: Greg KH <gregkh@linuxfoundation.org>
To: Zhong Jinghua <zhongjinghua@huawei.com>
Cc: jejb@linux.ibm.com, martin.petersen@oracle.com, hare@suse.de,
	bvanassche@acm.org, emilne@redhat.com,
	linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org,
	yi.zhang@huawei.com, yukuai3@huawei.com
Subject: Re: [PATCH-next v2 1/2] driver core: introduce get_device_unless_zero()
Date: Sat, 28 Jan 2023 11:43:20 +0100	[thread overview]
Message-ID: <Y9T8SION2vDlmaSa@kroah.com> (raw)
In-Reply-To: <20230128094146.205858-2-zhongjinghua@huawei.com>

On Sat, Jan 28, 2023 at 05:41:45PM +0800, Zhong Jinghua wrote:
> When the dev reference count is 0, calling get_device will go from 0 to 1,

You can NOT have a device reference count that is 0.  If you do, you are
doing something really really wrong, and there's a bug somewhere else.

> which will cause errors in some place of the kernel.

It's already an error in the kernel that tries to increment a reference
count of 0 as that device is already freed and you are working with
memory that is not present.

> So introduce a
> get_devcie_unless_zero method that returns NULL when the dev reference
> count is 0.

No, this is not ok, sorry, please never do this.  Fix the caller.

thanks,

greg k-h