On Thu 02-11-17 10:16:49, Pavel Tatashin wrote:
> > > > > Now, that memory is not zeroed, page_is_buddy() can return true after kexec
> > > > > when memory is dirty (unfortunately memset(1) with CONFIG_VM_DEBUG does not
> > > > > catch this case). And proceed further to incorrectly remove buddy from the
> > > > > list.
> > > >
> > > > OK, I thought this was a regression from one of the recent patches. So
> > > > the problem is not new. Why don't we see the same problem during the
> > > > standard boot?
> > >
> > > Because, I believe, BIOS is zeroing all the memory for us.
> >
> > I thought you were runnning with the debugging which poisons all the
> > allocated memory...
>
> Yes, but as I said, unfortunately memset(1) with CONFIG_VM_DEBUG does not
> catch this case. So, when CONFIG_VM_DEBUG is enabled kexec reboots without
> issues.
Can we make the init pattern to catch this?
> > > > > This is why we must initialize the computed buddy page beforehand.
> > > >
> > > > Ble, this is really ugly. I will think about it more.
> > > >
> > >
> > > Another approach that I considered is to split loop inside
> > > deferred_init_range() into two loops: one where we initialize pages by
> > > calling __init_single_page(), another where we free them to buddy allocator
> > > by calling deferred_free_range().
> >
> > Yes, that would make much more sense to me.
> >
>
> Ok, so should I submit a new patch with two loops? (The logic within loops
> is going to be the same:
Could you post it please?
> if (!pfn_valid_within(pfn)) {
> } else if (!(pfn & nr_pgmask) && !pfn_valid(pfn)) {
> } else if (!meminit_pfn_in_nid(pfn, nid, &nid_init_state)) {
> } else if (page && (pfn & nr_pgmask)) {
>
> This fix was already added into mm-tree as
> mm-deferred_init_memmap-improvements-fix-2.patch
I think Andrew can drop it and replace by a different patch.
--
Michal Hocko
SUSE Labs
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