Re: read_pnode: error -22 reading pnode at XX:YYYYY

[Artem Bityutskiy <dedekind1@gmail.com>]

On Thu, 2011-05-05 at 16:07 -0500, Rick Johnson wrote:
> Hi Artem,
> 
> Thanks for your advice!  We were finally able to reproduce the problem.
> 
> > 1. Validate the pnode before packing, do the same validate_pnode() does.
> > May be you'll catch the place where it we write incorrect pnode. Because
> > what you see is a result of an error which might have happend long
> > before you hit it.
> 
> We did validate_pnode() before the pnode was packed and have this output 
> from dbg_dump_pnode():
> 
> (pid 6298) dumping pnode:
> 	address c631d380 parent c6005720 cnext c6005720
> 	flags 3 iip 3 level 0 num -969086448
> 	0: free 0 dirty 127984 flags 1 lnum 514
> 	1: free 129024 dirty 0 flags 4 lnum 515
> 	2: free 0 dirty 127920 flags 1 lnum 516
> 	3: free 129024 dirty 0 flags 4 lnum 517
> 
> 
> It looks like 'num' is not valid.  Also, is it normal for 'parent' to be 
> equal to 'cnext'?

This code was written by Adiran and I do not know it, and it was a
little of "very quick programming", so it is not the cleanest code in
UBIFS, sorry.

I do not know by heart, but I think cnext is about the list of nodes
which should be written to the flash at the next commit. So if ->cnext
== ->parent this means that our parent is the next in the list. Hmm, and
I think we dirty nodes in the LPT tree from the bottom up to the root,
and add them to the commit list (cnext), so cnext == parent should be
very common.

But in 'read_pnode()' cnext must be NULL, I think.

Anyway, as I said, that was not my code, so I myself have difficulties
to deal with it. I asked Adrian to help  - may be he'll take a look at
this if he has time.

> We'll continue to look into this, but I thought it wouldn't hurt to get 
> your opinion on the above debug.

Sure. I hope you'll nail this. How well is it reproducible? Can you
reproduce this on nandsim which has equivalent characteristics (PEB
size, page size, count of PEBs) ?

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)