Re: [EDAC PATCH v13 5/7] edac: rewrite edac_align_ptr()

[Borislav Petkov]

On Mon, Apr 16, 2012 at 05:12:11PM -0300, Mauro Carvalho Chehab wrote:
> The edac_align_ptr() function is used to prepare data for a single
> memory allocation kzalloc() call. It counts how many bytes are needed
> by some data structure.
> 
> Using it as-is is not that trivial, as the quantity of memory elements
> reserved is not there, but, instead, it is on a next call.
> 
> In order to avoid mistakes when using it, move the number of allocated
> elements into it, making easier to use it.
> 
> Reviewed-by: Aristeu Rozanski <arozansk@xxxxxxxxxx>

AFAICT, this is a new patch so Aristeu cannot have reviewed it too. In
such case, you can't simply keep the Reviewed-by tagging. Unless he
really did that and I missed his mail with the tag somehow...?

> Cc: Doug Thompson <norsk5@xxxxxxxxx>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
> ---
>  drivers/edac/edac_device.c |   27 +++++++++++----------------
>  drivers/edac/edac_mc.c     |   19 +++++++++++++------
>  drivers/edac/edac_module.h |    2 +-
>  drivers/edac/edac_pci.c    |    7 ++++---
>  4 files changed, 29 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/edac/edac_device.c b/drivers/edac/edac_device.c
> index 4b15459..cb397d9 100644
> --- a/drivers/edac/edac_device.c
> +++ b/drivers/edac/edac_device.c
> @@ -79,7 +79,7 @@ struct edac_device_ctl_info *edac_device_alloc_ctl_info(
>  	unsigned total_size;
>  	unsigned count;
>  	unsigned instance, block, attr;
> -	void *pvt;
> +	void *pvt, *p;
>  	int err;
>  
>  	debugf4("%s() instances=%d blocks=%d\n",
> @@ -92,35 +92,30 @@ struct edac_device_ctl_info *edac_device_alloc_ctl_info(
>  	 * to be at least as stringent as what the compiler would
>  	 * provide if we could simply hardcode everything into a single struct.
>  	 */
> -	dev_ctl = (struct edac_device_ctl_info *)NULL;
> +	p = NULL;
> +	dev_ctl = edac_align_ptr(&p, sizeof(*dev_ctl), 1);
>  
>  	/* Calc the 'end' offset past end of ONE ctl_info structure
>  	 * which will become the start of the 'instance' array
>  	 */
> -	dev_inst = edac_align_ptr(&dev_ctl[1], sizeof(*dev_inst));
> +	dev_inst = edac_align_ptr(&p, sizeof(*dev_inst), nr_instances);
>  
>  	/* Calc the 'end' offset past the instance array within the ctl_info
>  	 * which will become the start of the block array
>  	 */
> -	dev_blk = edac_align_ptr(&dev_inst[nr_instances], sizeof(*dev_blk));
> +	count = nr_instances * nr_blocks;
> +	dev_blk = edac_align_ptr(&p, sizeof(*dev_blk), count);
>  
>  	/* Calc the 'end' offset past the dev_blk array
>  	 * which will become the start of the attrib array, if any.
>  	 */
> -	count = nr_instances * nr_blocks;
> -	dev_attrib = edac_align_ptr(&dev_blk[count], sizeof(*dev_attrib));
> -
> -	/* Check for case of when an attribute array is specified */
> -	if (nr_attrib > 0) {
> -		/* calc how many nr_attrib we need */
> +	/* calc how many nr_attrib we need */
> +	if (nr_attrib > 0)
>  		count *= nr_attrib;
> +	dev_attrib = edac_align_ptr(&p, sizeof(*dev_attrib), count);
>  
> -		/* Calc the 'end' offset past the attributes array */
> -		pvt = edac_align_ptr(&dev_attrib[count], sz_private);
> -	} else {
> -		/* no attribute array specificed */
> -		pvt = edac_align_ptr(dev_attrib, sz_private);
> -	}
> +	/* Calc the 'end' offset past the attributes array */
> +	pvt = edac_align_ptr(&p, sz_private, 1);
>  
>  	/* 'pvt' now points to where the private data area is.
>  	 * At this point 'pvt' (like dev_inst,dev_blk and dev_attrib)
> diff --git a/drivers/edac/edac_mc.c b/drivers/edac/edac_mc.c
> index ffedae9..98de5d1 100644
> --- a/drivers/edac/edac_mc.c
> +++ b/drivers/edac/edac_mc.c
> @@ -108,9 +108,12 @@ EXPORT_SYMBOL_GPL(edac_mem_types);
>   * If 'size' is a constant, the compiler will optimize this whole function
>   * down to either a no-op or the addition of a constant to the value of 'ptr'.
>   */
> -void *edac_align_ptr(void *ptr, unsigned size)
> +void *edac_align_ptr(void **p, unsigned size, int quant)

Oh, no, pls write it out as 'quantity'. 'quant' only means nothing...
ok, it does but it does not fit in this here context:

>From The Collaborative International Dictionary of English v.0.48 [gcide]:

  Quant \Quant\, n.
     A punting pole with a broad flange near the end to prevent it
     from sinking into the mud; a setting pole.
     [1913 Webster]

:-)

>  {
>  	unsigned align, r;
> +	void *ptr = *p;
> +
> +	*p += size * quant;
>  
>  	/* Here we assume that the alignment of a "long long" is the most
>  	 * stringent alignment that the compiler will ever provide by default.
> @@ -132,6 +135,8 @@ void *edac_align_ptr(void *ptr, unsigned size)
>  	if (r == 0)
>  		return (char *)ptr;
>  
> +	*p += align - r;
> +

Why increment *p here too - we're returning ptr below? Or are we keeping
the alignment in the original pointer too? Why can't we pass the aligned
pointer from the previous pass? I.e., do

	p = NULL;
	dev_ctl = edac_align_ptr(&p, sizeof(*dev_ctl), 1);

and then do

	dev_inst = edac_align_ptr(&dev_ctl, sizeof(*dev_inst), nr_instances);

In any case, this is not trivial so the function needs a bunch of comments.

>  	return (void *)(((unsigned long)ptr) + align - r);
>  }
>  
> @@ -154,6 +159,7 @@ void *edac_align_ptr(void *ptr, unsigned size)
>  struct mem_ctl_info *edac_mc_alloc(unsigned sz_pvt, unsigned nr_csrows,
>  				unsigned nr_chans, int edac_index)
>  {
> +	void *ptr;
>  	struct mem_ctl_info *mci;
>  	struct csrow_info *csi, *csrow;
>  	struct rank_info *chi, *chp, *chan;
> @@ -168,11 +174,12 @@ struct mem_ctl_info *edac_mc_alloc(unsigned sz_pvt, unsigned nr_csrows,
>  	 * stringent as what the compiler would provide if we could simply
>  	 * hardcode everything into a single struct.
>  	 */
> -	mci = (struct mem_ctl_info *)0;
> -	csi = edac_align_ptr(&mci[1], sizeof(*csi));
> -	chi = edac_align_ptr(&csi[nr_csrows], sizeof(*chi));
> -	dimm = edac_align_ptr(&chi[nr_chans * nr_csrows], sizeof(*dimm));
> -	pvt = edac_align_ptr(&dimm[nr_chans * nr_csrows], sz_pvt);
> +	ptr = 0;

Declare it above like this:

	void *ptr = NULL;

> +	mci = edac_align_ptr(&ptr, sizeof(*mci), 1);
> +	csi = edac_align_ptr(&ptr, sizeof(*csi), nr_csrows);
> +	chi = edac_align_ptr(&ptr, sizeof(*chi), nr_csrows * nr_chans);
> +	dimm = edac_align_ptr(ptr, sizeof(*dimm), nr_csrows * nr_chans);
> +	pvt = edac_align_ptr(&ptr, sz_pvt, 1);
>  	size = ((unsigned long)pvt) + sz_pvt;
>  
>  	mci = kzalloc(size, GFP_KERNEL);
> diff --git a/drivers/edac/edac_module.h b/drivers/edac/edac_module.h
> index 00f81b4..0be4b01 100644
> --- a/drivers/edac/edac_module.h
> +++ b/drivers/edac/edac_module.h
> @@ -50,7 +50,7 @@ extern void edac_device_reset_delay_period(struct edac_device_ctl_info
>  					   *edac_dev, unsigned long value);
>  extern void edac_mc_reset_delay_period(int value);
>  
> -extern void *edac_align_ptr(void *ptr, unsigned size);
> +extern void *edac_align_ptr(void **p, unsigned size, int quant);
>  
>  /*
>   * EDAC PCI functions
> diff --git a/drivers/edac/edac_pci.c b/drivers/edac/edac_pci.c
> index 63af1c5..9016560 100644
> --- a/drivers/edac/edac_pci.c
> +++ b/drivers/edac/edac_pci.c
> @@ -42,13 +42,14 @@ struct edac_pci_ctl_info *edac_pci_alloc_ctl_info(unsigned int sz_pvt,
>  						const char *edac_pci_name)
>  {
>  	struct edac_pci_ctl_info *pci;
> -	void *pvt;
> +	void *p, *pvt;
>  	unsigned int size;
>  
>  	debugf1("%s()\n", __func__);
>  
> -	pci = (struct edac_pci_ctl_info *)0;
> -	pvt = edac_align_ptr(&pci[1], sz_pvt);
> +	p = 0;

ditto.

> +	pci = edac_align_ptr(&p, sizeof(*pci), 1);
> +	pvt = edac_align_ptr(&p, 1, sz_pvt);
>  	size = ((unsigned long)pvt) + sz_pvt;
>  
>  	/* Alloc the needed control struct memory */
> -- 
> 1.7.8
> 
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-- 
Regards/Gruss,
Boris.

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