On 06/02/21 at 05:02am, HAGIO KAZUHITO(萩尾 一仁) wrote:
> -----Original Message-----
> > On 06/02/21 at 01:11am, HAGIO KAZUHITO(萩尾 一仁) wrote:
> > > -----Original Message-----
> > > > On Tue, 1 Jun 2021 10:40:09 +0200 David Hildenbrand <david@xxxxxxxxxx> wrote:
> > > >
> > > > > > Thanks, i explained the reason during my last reply.
> > > > > > Andrew has already picked this patch to -mm tree.
> > > > >
> > > > > Just because it's in Andrews tree doesn't mean it will end up upstream. ;)
> > > > >
> > > > > Anyhow, no really strong opinion, it's simply unnecessary code churn
> > > > > that makes bisecting harder without real value IMHO.
> > > >
> > > > I think it's a good change - mem_sections refers to multiple instances
> > > > of a mem_section. Churn is a pain, but that's the price we pay for more
> > > > readable code. And for having screwed it up originally ;)
> > >
> > > From a makedumpfile/crash-utility viewpoint, I don't deny kernel improvement
> > > and probably the change will not be hard for them to support, but I'd like
> > > you to remember that the tool users will need to update them for the change.
> >
> > As VIM user, I can understand Aisheng's feeling on the mem_section
> > variable which has the same symbol name as its type. Meanwhile it does
> > cause makedumpfile/crash having to be changed accordingly.
> >
> > Maybe we can carry it when any essential change is needed in both kernel
> > and makedumpfile/crash around it.
>
> Yes, that is a possible option.
>
> >
> > >
> > > The situation where we need to update the tools for new kernels is usual, but
> > > there are not many cases that they cannot even start session, and this change
> >
> > By the way, Kazu, about a case starting session, could you be more specific
> > or rephrase? I may not get it clearly. Thanks.
>
> As for the current crash, the "mem_section" symbol is used to determine
> which memory model is used.
>
> if (kernel_symbol_exists("mem_section"))
> vt->flags |= SPARSEMEM;
> else if (kernel_symbol_exists("mem_map")) {
> get_symbol_data("mem_map", sizeof(char *), &vt->mem_map);
> vt->flags |= FLATMEM;
> } else
> vt->flags |= DISCONTIGMEM;
>
> So without updating, crash will assume that the memory model is DISCONTIGMEM,
> fail during vm_init() and cannot start a session. This is an imitation of
> the situation though:
>
> - if (kernel_symbol_exists("mem_section"))
> + if (kernel_symbol_exists("mem_sectionX"))
>
> # crash
> ...
> crash: invalid structure member offset: pglist_data_node_mem_map
> FILE: memory.c LINE: 16420 FUNCTION: dump_memory_nodes()
>
> [/root/bin/crash] error trace: 465304 => 4ac2bf => 4aae19 => 57f4d7
>
> 57f4d7: OFFSET_verify+164
> 4aae19: dump_memory_nodes+5321
> 4ac2bf: vm_init+4031
> 465304: main_loop+392
>
> #
>
> Every time a kernel is released, there are some changes that crash can
> start up with but cannot run a specific crash's command, but a change
> that crash cannot start up like this case does not occur often.
Ah,I see. You mean this patch will cause startup failure of crash/makedumpfile
during application's earlier stage, and this is a severer situation than
others. Then we may need defer the patch acceptance to a future suitable
time. Thanks for explanation.
>
> Also as for makedumpfile, the "SYMBOL(mem_section)" vmcore entry is used
> to determine the memory model, so it will fail with the following error
> without an update.
>
> # ./makedumpfile --mem-usage /proc/kcore
> get_mem_map: Can't distinguish the memory type.
>
> makedumpfile Failed.
>
> Thanks,
> Kazu
