[Crash-utility] [RFC PATCH] struct: Fix handing of percpu symbols

[Dave Anderson]

----- Original Message -----
> On Thu 2016-04-21 14:59 -0400, Dave Anderson wrote:
> 
> Hi Dave,
> 
> > Sorry for the delay in getting around to testing this patch.
> 
> No problem at all.
> 
> > My first test attempt was with the kmalloc-32 slab freelist corruption vmcores
> > that I'm looking at, just because they involve the kmem_cache data structure,
> > which contains a per-cpu pointer to each cpu's the kmem_cache_cpu structure:
> > 
> >   struct kmem_cache {
> >         struct kmem_cache_cpu __percpu *cpu_slab;
> >         ...
> 
> [ ... ]
> 
> > Now, with your patch applied, I get this:
> > 
> >   crash> kmem_cache_cpu 163c0:a
> >   struct: invalid percpu symbol value: 163c0
> >   crash>
> > 
> > I tried it both with your original patch, and with your original patch
> > with your updated open_tmpfile() segment jammed in.
> 
> IIUC, the cpu_slab object is allocated from the dynamic percpu area.
> Unfortunately the patch only takes into consideration static in-kernel
> percpu symbols i.e. those between the range of __per_cpu_start and
> __per_cpu_end.
> 
> Not sure how to test for such percpu symbols at the moment.
> 
> Looking at the patch again perhaps the following is more suitable for
> per_cpu_symbol_value_search():
> 
> --- a/symbols.c
> +++ b/symbols.c
> @@ -5181,7 +5181,8 @@ per_cpu_symbol_value_search(ulong value)
>         if ((sp = symval_hash_search(value)) == NULL)
>                 sp = st->symtable;
> 
> -       for (; sp < st->symend; sp++)
> +       for (; sp < st->__per_cpu_end; sp++)
> +
>                 if (value == sp->value)
>                         return sp = __per_cpu_symbol_search(sp->name);
> 
> 
> 
> --
> Aaron Tomlin
> 

May be, but I don't have the patched/patch build set up any more.

I'm going to defer this until 7.1.6 because I really need to get 7.1.5 out
the door and I can't risk breaking basic functionality.  So that will give
you some time to put together and test your next patch set.  Sound reasonable?

Thanks,
  Dave