Re: [PATCH 0/2] mm, memory_hotplug: fix uninitialized pages fallouts.

[Michal Hocko]

On Tue 29-01-19 14:14:47, Gerald Schaefer wrote:
> On Mon, 28 Jan 2019 15:45:04 +0100
> Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> 
> > Hi,
> > Mikhail has posted fixes for the two bugs quite some time ago [1]. I
> > have pushed back on those fixes because I believed that it is much
> > better to plug the problem at the initialization time rather than play
> > whack-a-mole all over the hotplug code and find all the places which
> > expect the full memory section to be initialized. We have ended up with
> > 2830bf6f05fb ("mm, memory_hotplug: initialize struct pages for the full
> > memory section") merged and cause a regression [2][3]. The reason is
> > that there might be memory layouts when two NUMA nodes share the same
> > memory section so the merged fix is simply incorrect.
> > 
> > In order to plug this hole we really have to be zone range aware in
> > those handlers. I have split up the original patch into two. One is
> > unchanged (patch 2) and I took a different approach for `removable'
> > crash. It would be great if Mikhail could test it still works for his
> > memory layout.
> > 
> > [1] http://lkml.kernel.org/r/20181105150401.97287-2-zaslonko@xxxxxxxxxxxxx
> > [2] https://bugzilla.redhat.com/show_bug.cgi?id=1666948
> > [3] http://lkml.kernel.org/r/20190125163938.GA20411@xxxxxxxxxxxxxx
> 
> I verified that both patches fix the issues we had with valid_zones
> (with mem=2050M) and removable (with mem=3075M).
> 
> However, the call trace in the description of your patch 1 is wrong.
> You basically have the same call trace for test_pages_in_a_zone in
> both patches. The "removable" patch should have the call trace for
> is_mem_section_removable from Mikhails original patches:

Thanks for testing. Can I use you Tested-by?

>  CONFIG_DEBUG_VM_PGFLAGS=y
>  kernel parameter mem=3075M
>  --------------------------
>  page:000003d08300c000 is uninitialized and poisoned
>  page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
>  Call Trace:
>  ([<000000000038596c>] is_mem_section_removable+0xb4/0x190)
>   [<00000000008f12fa>] show_mem_removable+0x9a/0xd8
>   [<00000000008cf9c4>] dev_attr_show+0x34/0x70
>   [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148
>   [<00000000003e4194>] seq_read+0x204/0x480
>   [<00000000003b53ea>] __vfs_read+0x32/0x178
>   [<00000000003b55b2>] vfs_read+0x82/0x138
>   [<00000000003b5be2>] ksys_read+0x5a/0xb0
>   [<0000000000b86ba0>] system_call+0xdc/0x2d8
>  Last Breaking-Event-Address:
>   [<000000000038596c>] is_mem_section_removable+0xb4/0x190
>  Kernel panic - not syncing: Fatal exception: panic_on_oops

Yeah, this is c&p mistake on my end. I will use this trace instead.
Thanks for spotting.
-- 
Michal Hocko
SUSE Labs