From: Anthony Martin <ality@pbrane.org>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: Re: [9fans] kernel bug
Date: Mon, 2 Jun 2014 23:00:15 -0700 [thread overview]
Message-ID: <20140603060015.GA28564@dinah> (raw)
In-Reply-To: <C29EB1DC-4A22-4149-9510-3054933D77C5@fb.com>
Yoann Padioleau <pad@fb.com> once said:
> in the newseg() function there is:
>
> [...]
>
> I think it should be
> if(mapsize > (SEGMAPSIZE))
> mapsize = SEGMAPSIZE;
Yes, you're correct.
The code allows the creation of a segment VM map with more
than SEGMAPSIZE Ptes.
Personally, I'd remove the check entirely along with the
optimization of doubling the segment size, perhaps moving
it to ibrk. I think it's more likely that the segment will
grow if brk is called at least once.
Anthony
P.S. It looks like this is a 15 year old bug:
1998/0916/sys/src/9/port/segment.c:62,67 - 1998/0919/sys/src/9/port/segment.c:62,70
mapsize = ROUND(size, PTEPERTAB)/PTEPERTAB;
if(mapsize > nelem(s->ssegmap)){
+ mapsize *= 2;
+ if(mapsize > (SEGMAPSIZE*PTEPERTAB))
+ mapsize = (SEGMAPSIZE*PTEPERTAB);
s->map = smalloc(mapsize*sizeof(Pte*));
s->mapsize = mapsize;
}
next prev parent reply other threads:[~2014-06-03 6:00 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-03 1:14 Yoann Padioleau
2014-06-03 5:49 ` cinap_lenrek
2014-06-03 6:00 ` Anthony Martin [this message]
2014-06-03 15:47 ` erik quanstrom
2014-06-03 15:56 ` andrey mirtchovski
2014-06-03 16:04 ` erik quanstrom
2014-06-04 19:12 ` Anthony Martin
2014-06-03 16:08 ` Charles Forsyth
2014-06-03 17:08 ` erik quanstrom
2014-06-03 18:04 ` Charles Forsyth
2014-06-03 18:09 ` Charles Forsyth
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