NAND buffer allocation fails

NAND buffer allocation fails

[Tony Prisk]

Could someone explain why the following situation might occur:

In drivers/mtd/nand/nand_base.c, we have:

int nand_scan_tail(struct mtd_info *mtd)
{
     int i;
     struct nand_chip *chip = mtd->priv;

     /* New bad blocks should be marked in OOB, flash-based BBT, or both */
     BUG_ON((chip->bbt_options & NAND_BBT_NO_OOB_BBM) &&
             !(chip->bbt_options & NAND_BBT_USE_FLASH));

     if (!(chip->options & NAND_OWN_BUFFERS))
         chip->buffers = kmalloc(sizeof(*chip->buffers), GFP_KERNEL);
     if (!chip->buffers)
         return -ENOMEM;
...

For some reason, the kmalloc always fails on my configuration/hardware 
(arch-vt8500: WonderMedia/VIA APC8750).

The strange thing is that if I add the NAND_OWN_BUFFERS option, and 
allocate my own buffers in the driver probe everything is fine.
Driver probe code below:

     priv->nand.buffers = devm_kzalloc(priv->dev, 
sizeof(*priv->nand.buffers), GFP_KERNEL);
     if (!priv->nand.buffers) {
         dev_err(priv->dev, "failed to allocate NAND buffers\n");
         return -ENOMEM;
     }

The devm_kzalloc does occur earlier than the nand_scan_tail alloc would 
have, but there doesn't appear to be a shortage of memory on the 
platform so I don't think it's failing for a memory shortage.

Is there any real difference between using kmalloc and devm_kzalloc to 
allocate the buffer (other than the obvious 0'ing of the buffer)?
Why would one call fail and the other succeed?

Regards
Tony Prisk

Re: NAND buffer allocation fails

[Tony Prisk]

On 07/06/13 21:03, Tony Prisk wrote:
> Could someone explain why the following situation might occur:
>
> In drivers/mtd/nand/nand_base.c, we have:
>
> int nand_scan_tail(struct mtd_info *mtd)
> {
>     int i;
>     struct nand_chip *chip = mtd->priv;
>
>     /* New bad blocks should be marked in OOB, flash-based BBT, or 
> both */
>     BUG_ON((chip->bbt_options & NAND_BBT_NO_OOB_BBM) &&
>             !(chip->bbt_options & NAND_BBT_USE_FLASH));
>
>     if (!(chip->options & NAND_OWN_BUFFERS))
>         chip->buffers = kmalloc(sizeof(*chip->buffers), GFP_KERNEL);
>     if (!chip->buffers)
>         return -ENOMEM;
> ...
>
> For some reason, the kmalloc always fails on my configuration/hardware 
> (arch-vt8500: WonderMedia/VIA APC8750).
>
> The strange thing is that if I add the NAND_OWN_BUFFERS option, and 
> allocate my own buffers in the driver probe everything is fine.
> Driver probe code below:
>
>     priv->nand.buffers = devm_kzalloc(priv->dev, 
> sizeof(*priv->nand.buffers), GFP_KERNEL);
>     if (!priv->nand.buffers) {
>         dev_err(priv->dev, "failed to allocate NAND buffers\n");
>         return -ENOMEM;
>     }
>
> The devm_kzalloc does occur earlier than the nand_scan_tail alloc 
> would have, but there doesn't appear to be a shortage of memory on the 
> platform so I don't think it's failing for a memory shortage.
>
> Is there any real difference between using kmalloc and devm_kzalloc to 
> allocate the buffer (other than the obvious 0'ing of the buffer)?
> Why would one call fail and the other succeed?
>
> Regards
> Tony Prisk

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Tony P