linux-kernel - Re: [PATCH] nvmem: fix unregistering device in nvmem

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Date:   Tue, 21 Dec 2021 17:06:23 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Rafał Miłecki <zajec5@...il.com>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Johan Hovold <johan@...nel.org>,
        Andrey Smirnov <andrew.smirnov@...il.com>,
        linux-kernel@...r.kernel.org,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH] nvmem: fix unregistering device in nvmem_register()
 error path

On Tue, Dec 21, 2021 at 04:45:50PM +0100, Rafał Miłecki wrote:
> From: Rafał Miłecki <rafal@...ecki.pl>
> 
> 1. Drop incorrect put_device() calls
> 
> If device_register() fails then underlaying device_add() takes care of
> calling put_device() if needed. There is no need to do that in a driver.

Did you read the documentation for device_register() that says:

 * NOTE: _Never_ directly free @dev after calling this function, even
 * if it returned an error! Always use put_device() to give up the
 * reference initialized in this function instead.

> 2. Use device_unregister()
> 
> Now that we don't call put_device() we can use above helper.
> 
> Fixes: 3360acdf8391 ("nvmem: core: fix leaks on registration errors")
> Cc: Johan Hovold <johan@...nel.org>
> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
> ---
> That put_device() was explicitly added by Johan but after checking
> device_register() twice I still think it's incorrect. I hope I didn't
> miss sth obvious and I didn't mess it up.
> ---
>  drivers/nvmem/core.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 785a56e33f69..f7f31af7226f 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -901,12 +901,12 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
>  
>  	rval = device_register(&nvmem->dev);
>  	if (rval)
> -		goto err_put_device;
> +		return ERR_PTR(rval);

Where do you call put_device() to free the allocated memory?

You just leaked the kzalloc() call to allocate the memory pointed to by
nvmem :(

I think the code is fine as-is.

thanks,

greg k-h