linux-kernel - Re: [PATCH 1/2] mtd: use put_device() if device

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Date:   Sat, 17 Mar 2018 15:15:45 +0530
From:   arvindY <arvind.yadav.cs@...il.com>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     dwmw2@...radead.org, computersforpeace@...il.com,
        boris.brezillon@...e-electrons.com, marek.vasut@...il.com,
        richard@....at, cyrille.pitchen@...ev4u.fr, dedekind1@...il.com,
        linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org
Subject: Re: [PATCH 1/2] mtd: use put_device() if device_register fail



On Wednesday 14 March 2018 08:06 PM, Boris Brezillon wrote:
> On Fri,  9 Mar 2018 16:20:48 +0530
> Arvind Yadav <arvind.yadav.cs@...il.com> wrote:
>
>> if device_register() returned an error! Always use put_device()
>> to give up the reference initialized.
>>
>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@...il.com>
>> ---
>>   drivers/mtd/mtdcore.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
>> index 28553c8..4d77ca2 100644
>> --- a/drivers/mtd/mtdcore.c
>> +++ b/drivers/mtd/mtdcore.c
>> @@ -586,6 +586,7 @@ int add_mtd_device(struct mtd_info *mtd)
>>   	return 0;
>>   
>>   fail_added:
>> +	put_device(&mtd->dev);
> Not sure this is a good idea: the put_device() call will trigger
> an mtd_devtype->release(), which will in turn call device_destroy() on
> something that does not exist yet. Not sure if this is a real problem,
> but it does not look like the right thing to do.
>
yes, you are correct. No need to call put_device().
which can cause other problem.

>>   	of_node_put(mtd_get_of_node(mtd));
> You're referencing an object that is supposed to have been
> freed/released by the put_device() call. Again, it's not really a
> problem because in our case ->release() does not free the mtd object
> (as is usually done in other parts of the kernel), but it still looks
> wrong. It's probably better to move the of_node_put() and the below
> idr_remove() call in the ->release() hook if you want to use
> put_device().
>
>>   	idr_remove(&mtd_idr, i);
Sure, we can move put_device() below this. But need to check
how we can add hook in release.
>
>>   fail_locked:
>
>
~arvind