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Date: Tue, 4 Aug 2015 15:55:56 +0300
From: Dan Carpenter <dan.carpenter@oracle.com>
To: Julia Lawall <julia.lawall@lip6.fr>
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Cc: Shuah Khan <shuah.kh@samsung.com>, Russell King <linux@arm.linux.org.uk>,
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	Christoph Hellwig <hch@infradead.org>, Tejun Heo <tj@kernel.org>
Subject: Re: [Ksummit-discuss] [TECH TOPIC] Fix devm_kzalloc, its users,
 or both
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On Sat, Aug 01, 2015 at 01:21:09PM +0200, Julia Lawall wrote:
> Currently, is there any documentation about when these functions can be
> used?  All I remember seeing is a discussion of what the functions do and
> what functions are available.  But nothing about when they should and
> should not be used.
> 

The documentation for devm_kmalloc() doesn't list common pitfalls.  The
other big one which should be obvious, but happens often is freeing
devm_ memory with kfree().

/**
 * devm_kmalloc - Resource-managed kmalloc
 * @dev: Device to allocate memory for
 * @size: Allocation size
 * @gfp: Allocation gfp flags
 *
 * Managed kmalloc.  Memory allocated with this function is
 * automatically freed on driver detach.  Like all other devres
 * resources, guaranteed alignment is unsigned long long.
 *
 * RETURNS:
 * Pointer to allocated memory on success, NULL on failure.
 */

Another thing which I have seems fairly common is treating it like
kmalloc() and calling devm_kfree() manually.  For example, ssp_parse_dt()

drivers/iio/common/ssp_sensors/ssp_dev.c
   493          return data;
   494  
   495  err_mcu_reset_gpio:
   496          devm_gpio_free(dev, data->mcu_reset_gpio);
   497  err_ap_mcu:
   498          devm_gpio_free(dev, data->ap_mcu_gpio);
   499  err_free_pd:
   500          devm_kfree(dev, data);
   501          return NULL;
   502  }

regards,
dan carpenter