linux-kernel - Re: [PATCH v7 1/3] devres: provide devm

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Date:   Mon, 17 Aug 2020 20:39:08 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Michal Simek <michal.simek@...inx.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <linux@...ck-us.net>, linux-iio@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v7 1/3] devres: provide devm_krealloc()

On Mon, Aug 17, 2020 at 07:05:33PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> 
> Implement the managed variant of krealloc(). This function works with
> all memory allocated by devm_kmalloc() (or devres functions using it
> implicitly like devm_kmemdup(), devm_kstrdup() etc.).
> 
> Managed realloc'ed chunks can be manually released with devm_kfree().

Thanks for an update! My comments / questions below.

...

> +static struct devres *to_devres(void *data)
> +{
> +	return (struct devres *)((u8 *)data - ALIGN(sizeof(struct devres),
> +						    ARCH_KMALLOC_MINALIGN));

Do you really need both explicit castings?

> +}

...

> +	total_old_size = ksize(to_devres(ptr));

But how you can guarantee this pointer:
 - belongs to devres,
 - hasn't gone while you run a ksize()?

...

> +	new_dr = alloc_dr(devm_kmalloc_release,
> +			  total_new_size, gfp, dev_to_node(dev));

Can you move some parameters to the previous line?

> +	if (!new_dr)
> +		return NULL;

...

> +	spin_lock_irqsave(&dev->devres_lock, flags);
> +
> +	old_dr = find_dr(dev, devm_kmalloc_release, devm_kmalloc_match, ptr);
> +	if (!old_dr) {
> +		spin_unlock_irqrestore(&dev->devres_lock, flags);
> +		devres_free(new_dr);
> +		WARN(1, "Memory chunk not managed or managed by a different device.");
> +		return NULL;
> +	}
> +
> +	replace_dr(dev, &old_dr->node, &new_dr->node);
> +
> +	spin_unlock_irqrestore(&dev->devres_lock, flags);
> +
> +	memcpy(new_dr->data, old_dr->data, devres_data_size(total_old_size));

But new_dr may concurrently gone at this point, no? It means memcpy() should be
under spin lock.

-- 
With Best Regards,
Andy Shevchenko