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Date:	Thu, 21 Nov 2013 10:42:18 +0800
From:	YuLicheng <gancuimian@...mail.com>
To:	<linux-doc@...r.kernel.org>
CC:	<linux-kernel@...r.kernel.org>, <roel.kluin@...il.com>
Subject: kref doc: Why kref kernel doc omits kref_put when kthread_run fail

The document is /Documentation/kerf.txt, and I'm referring to v3.12:
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/Documentation/kref.txt?id=v3.12

Part of the first example in the document is attached below.
In my_data_handler(), kref_init() already put 1 to refcount, and kref_get()
next made the refcount 2. But if kthread_run() fails, only one kref_put() 
will
take place (right after the out tag), it renders the refcount to be 1 at 
last,
and the data will never be freed.

int my_data_handler(void)
{
        int rv = 0;
        struct my_data *data;
        struct task_struct *task;
        data = kmalloc(sizeof(*data), GFP_KERNEL);
        if (!data)
                return -ENOMEM;
        kref_init(&data->refcount);

        kref_get(&data->refcount);
        task = kthread_run(more_data_handling, data, "more_data_handling");
        if (task == ERR_PTR(-ENOMEM)) {
                rv = -ENOMEM;
                goto out;
        }

        .
        . do stuff with data here
        .
out:
        kref_put(&data->refcount, data_release);
        return rv;
}

I also noticed that there once was a kref_put() before "goto out" in the doc
before some point of 2009, but it was removed by a patch that claimed that 
this
kref_put() was redudent.
The patch commit is:
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/Documentation/kref.txt?id=8f1ecc9fbc5b223e4f5d5bb8bcd6f5672c4bc4b6

Is this a bug or maybe I missed something?


        Licheng 

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