Re: Remove lots of IS_ERR_VALUE abuses and compilation warning.

[Guenter Roeck <linux@roeck-us.net>]

On Thu, Jul 07, 2016 at 08:57:29PM +0530, Arvind Yadav wrote:
> Passing value in IS_ERR_VALUE() is wrong, as they
>     pass an 'int' into a function that takes an 'unsigned long'
>     argument. This happens to work because the type is sign-extended
>     on 64-bit architectures before it gets converted into an
>     unsigned type.
> 
>     Passing an 'unsigned short' or 'unsigned int'
>     argument into IS_ERR_VALUE() is guaranteed to be broken, as are
>     8-bit integers and types that are wider than 'unsigned long'.
> 
>     Any user will get compilation warning for that do not pass an
>     'unsigned long' argument.
> 
>     Commit '287980e49f; - This change is alreday fixes lots of other
>     worst abusers.
> 
Couple of generic comments:

- Your patch subject lines don't include the affected drivers/modules.
  As such, most of them will be ignored because maintainers won't realize
  that you are talking with them. Some may ask you to resubmit with proper
  subject lines.
  Commit 287980e49f is different; it addresses the problem in several
  drivers in a single commit.
- If you patch a single file, I think it would be better to adjust the
  description accordingly. In this patch, the offending variable type is
  u32. The patch description is therefore misleading; the code here simply does
  not work.
- When you resubmit a patch, you don't include a version, not a change log.
  This means additional work for maintainers, who have to figure out which
  patch to apply.

Specific comment:

The allocator in question returns -ENOMEM in an unsigned long. This is assigned
to u32. A proper fix would be to assign the return value to an unsigned
long and to use IS_ER_VALUE() to check if it reports an error, and to only
assign it to ucc_fast_rx_virtual_fifo_base_offset if there was no error.

Also, unless I am missing something - since ucc_fast_rx_virtual_fifo_base_offset
is defined as u32, it is somewhat unlikely that it is ever < 0.

Guenter

> Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
> ---
>  drivers/soc/fsl/qe/ucc_fast.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/soc/fsl/qe/ucc_fast.c b/drivers/soc/fsl/qe/ucc_fast.c
> index a768931..7cc783c 100644
> --- a/drivers/soc/fsl/qe/ucc_fast.c
> +++ b/drivers/soc/fsl/qe/ucc_fast.c
> @@ -268,7 +268,7 @@ int ucc_fast_init(struct ucc_fast_info * uf_info, struct ucc_fast_private ** ucc
>  	/* Allocate memory for Tx Virtual Fifo */
>  	uccf->ucc_fast_tx_virtual_fifo_base_offset =
>  	    qe_muram_alloc(uf_info->utfs, UCC_FAST_VIRT_FIFO_REGS_ALIGNMENT);
> -	if (IS_ERR_VALUE(uccf->ucc_fast_tx_virtual_fifo_base_offset)) {
> +	if (uccf->ucc_fast_tx_virtual_fifo_base_offset < 0) {
>  		printk(KERN_ERR "%s: cannot allocate MURAM for TX FIFO\n",
>  			__func__);
>  		uccf->ucc_fast_tx_virtual_fifo_base_offset = 0;
> @@ -281,7 +281,7 @@ int ucc_fast_init(struct ucc_fast_info * uf_info, struct ucc_fast_private ** ucc
>  		qe_muram_alloc(uf_info->urfs +
>  			   UCC_FAST_RECEIVE_VIRTUAL_FIFO_SIZE_FUDGE_FACTOR,
>  			   UCC_FAST_VIRT_FIFO_REGS_ALIGNMENT);
> -	if (IS_ERR_VALUE(uccf->ucc_fast_rx_virtual_fifo_base_offset)) {
> +	if (uccf->ucc_fast_rx_virtual_fifo_base_offset < 0) {
>  		printk(KERN_ERR "%s: cannot allocate MURAM for RX FIFO\n",
>  			__func__);
>  		uccf->ucc_fast_rx_virtual_fifo_base_offset = 0;