Re: [Yaffs] [patch] Low memory edge-case assertion failure

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Author: Charles Manning
Date:  
To: yaffs
New-Topics: [Yaffs] Yaffs ECC/ spare byte overhead question
Subject: Re: [Yaffs] [patch] Low memory edge-case assertion failure
Fixed something...

On Wednesday 11 November 2009 12:59:07 Charles Manning wrote:
> Hi Ross
>
> Thanks for that patch.
>
> I had a look and have come up with an alternative solution to the problem:
> instead of trying to unwind a half created object if the string or tnode
> malloc fail it is a lot cleaner to reverse the order of allocation. ie
> forst create the tnode or string, then create the object if that succeeds.
>
> I also had a sniff around and found a few other areas where tnode creation
> failures would cause issues.
>
> The fixed stuff has been running in a stress test for almost 24 hours and
> I've just checked that in.
> http://www.aleph1.co.uk/cgi-bin/viewcvs.cgi/yaffs2/yaffs_guts.c?r1=1.93&r2=
>1.94

Look at:

http://www.aleph1.co.uk/cgi-bin/viewcvs.cgi/yaffs2/yaffs_guts.c?r1=1.95&r2=1.93
>
> I also put a day or so into extending low mem testing and will expand the
> tests more.
>
> Thanks
>
> -- Charles
>
> On Friday 30 October 2009 06:35:32 Ross Younger wrote:
> > Whilst doing some stress testing on a board with limited RAM, I tripped
> > over an assertion failure.
> >
> > In yaffs_CreateNewObject, YAFFS would sometimes successfully
> > AllocateEmptyObject but not be able to allocate a new tnode, so GetTnode
> > returned 0. It would then immediately attempt to FreeObject, but the
> > freshly allocated object already has a parent so it hits the YBUG trap at
> > line 1992 of yaffs_guts.c.
> >
> > I attach a patch which fixes this assertion (and a similar case I spotted
> > in yaffs_MknodObject) by calling DoGenericObjectDeletion instead of
> > FreeObject, though it might instead be reasonable for AllocateEmptyObject
> > to not try to add the object to the rootDir or lostNFoundDir.
> >
> >
> > Ross
>
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