linux-kernel - Re: [PATCH] mm: memory_hotplug: use put_device() if device

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Message-ID: <20180427145623.GC5404@dhcp22.suse.cz>
Date:   Fri, 27 Apr 2018 16:56:23 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Arvind Yadav <arvind.yadav.cs@...il.com>
Cc:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: memory_hotplug: use put_device() if device_register
 fail

On Thu 26-04-18 21:12:09, Arvind Yadav wrote:
> if device_register() returned an error. Always use put_device()
> to give up the initialized reference and release allocated memory.

Is this patch correct? The docummentation says
 * NOTE: _Never_ directly free @dev after calling this function, even
 * if it returned an error! Always use put_device() to give up your
 * reference instead.

but we do not have _our_ reference in this path AFAICS. Maybe this is
just a documentation issue? How have you tested this change btw.?

> Signed-off-by: Arvind Yadav <arvind.yadav.cs@...il.com>
> ---
>  drivers/base/memory.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index bffe861..f5e5601 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -649,13 +649,19 @@ static const struct attribute_group *memory_memblk_attr_groups[] = {
>  static
>  int register_memory(struct memory_block *memory)
>  {
> +	int ret;
> +
>  	memory->dev.bus = &memory_subsys;
>  	memory->dev.id = memory->start_section_nr / sections_per_block;
>  	memory->dev.release = memory_block_release;
>  	memory->dev.groups = memory_memblk_attr_groups;
>  	memory->dev.offline = memory->state == MEM_OFFLINE;
>  
> -	return device_register(&memory->dev);
> +	ret = device_register(&memory->dev);
> +	if (ret)
> +		put_device(&memory->dev);
> +
> +	return ret;
>  }
>  
>  static int init_memory_block(struct memory_block **memory,
> -- 
> 2.7.4

-- 
Michal Hocko
SUSE Labs