Re: IS_ERR Threshold Value

[Randy.Dunlap]

On Wed, 28 Jun 2006 14:57:07 -0600 Erik Frederiksen wrote:

> 
> from include/asm-mips/errno.h
> #define EDQUOT      1133    /* Quota exceeded */
> 
> I noticed that the errno value for EDQUOT on MIPS is considerably larger
> than all others.  This can lead to a situation where functions using
> ERR_PTR() to return error codes in pointers cannot return this error
> code without IS_ERR() thinking that the pointer is valid.  In my case,
> it caused an alignment exception in the XFS open call when quota has
> been exceeded in the linux-mips 2.6.14 kernel.  I think that the XFS
> code has changed enough that this bug isn't in newer versions, though I
> haven't done a thorough investigation.  
> 
> I've supplied a patch that addresses this situation by changing the
> threshold used by IS_ERR if EMAXERRNO is defined and greater than 1000. 
> Perhaps permanently raising the threshold value to something >1133 is
> sufficient.
> 
> Looking forward to your feedback.  
> 
> Erik Frederiksen
> Firmware Design Engineer Co-op
> PMC-Sierra Saskatoon

Hi,
Peter Anvin mentioned just a few days ago that this threshold value
should be 4095 for all arches.  I think we need to get that patch
done & submitted to Andrew for -mm.


> diff -Nau [ab]/include/linux/err.h
> --- a/include/linux/err.h       2005-10-30 13:14:22.000000000 -0600
> +++ b/include/linux/err.h       2006-06-28 10:38:43.000000000 -0600
> @@ -12,8 +12,23 @@
>   *
>   * This should be a per-architecture thing, to allow different
>   * error and pointer decisions.
> + *
> + * Updated by Erik Frederiksen (erik_frederiksen@xxxxxxxxxxxxxx)
> + * errno values on MIPS go up to 1133 for EDQUOT.  The threshold
> + * is adjusted so that returning large errnos in a pointer
> + * does not result in a valid pointer according to IS_ERR.
>   */
> -#define IS_ERR_VALUE(x) unlikely((x) > (unsigned long)-1000L)
> +
> +#define ERR_PTR_THRESHOLD 1000
> +#define IS_ERR_VALUE(x) \
> +       unlikely((x) > (unsigned long)-(long)ERR_PTR_THRESHOLD )
> +#ifdef EMAXERRNO
> +# if EMAXERRNO >= ERR_PTR_THRESHOLD
> +#  undef IS_ERR_VALUE
> +#  define IS_ERR_VALUE(x) \
> +       unlikely((x) >= (unsigned long)-(long)EMAXERRNO )
> +# endif
> +#endif
>   
>  static inline void *ERR_PTR(long error)
>  {
> 
> 
> -

---
~Randy
-
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