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

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