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Date: Wed, 28 Jun 2006 15:39:59 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: "Randy.Dunlap" <rdunlap@xenotime.net>
CC: Erik Frederiksen <erik_frederiksen@pmc-sierra.com>,
       linux-kernel@vger.kernel.org
Subject: Re: IS_ERR Threshold Value
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Randy.Dunlap wrote:
> 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.
> 

Indeed.

	-hpa