Re: Fix BUG_ON() reporting in real mode on powerpc

Balbir Singh [off-list ref] writes:

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Changelog:
     Don't add PAGE_OFFSET blindly, check if REGION_ID is 0

I ran into this issue while debugging an early boot problem.
The system hit a BUG_ON() but report bug failed to print the
line number and file name. The reason being that the system
was running in real mode and report_bug() searches for
addresses in the PAGE_OFFSET+ region

Suggested-by: Paul Mackerras <redacted>
Signed-off-by: Balbir Singh <bsingharora@gmail.com>

<snip>

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Can we add some comments around this. When i looked at this first, i was
wondering how nip can be in user region. But then realized that what we
are checking here is kernel address used in real mode. The use of
REGION_ID eventhough simpler is confusing. Hence adding the comment with
details Paul mentioned in email will help.

I've tried and covered it in the changelog, I thought a code comment
would make sense for the very non  obvious cases and not repeat what
the code does as comment

The use of REGION_ID indicate that you are checking for region. Hence
the suggestion. Looking at this again, I suggest we should add a new
macro or will have to open code it. Because in the radix series we make
REGION_ID a hash config thing and this is generic stuff. 

-aneesh