Date:   Fri, 7 Sep 2018 22:06:11 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     linux-kernel@...r.kernel.org, ard.biesheuvel@...aro.org,
        james.morse@....com, mpatocka@...hat.com,
        pavel.tatashin@...rosoft.com, will.deacon@....com,
        stable-commits@...r.kernel.org
Subject: Re: Patch "arm64: mm: always enable CONFIG_HOLES_IN_ZONE" has been
 added to the 4.9-stable tree

On Fri, Sep 07, 2018 at 11:36:01AM -0700, Nathan Chancellor wrote:
> On Fri, Sep 07, 2018 at 02:57:51PM +0200, gregkh@...uxfoundation.org wrote:
> > 
> > This is a note to let you know that I've just added the patch titled
> > 
> >     arm64: mm: always enable CONFIG_HOLES_IN_ZONE
> > 
> > to the 4.9-stable tree which can be found at:
> >     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> > 
> > The filename of the patch is:
> >      arm64-mm-always-enable-config_holes_in_zone.patch
> > and it can be found in the queue-4.9 subdirectory.
> > 
> > If you, or anyone else, feels it should not be added to the stable tree,
> > please let <stable@...r.kernel.org> know about it.
> > 
> > 
> > From f52bb98f5aded4c43e52f5ce19fb83f7261e9e73 Mon Sep 17 00:00:00 2001
> > From: James Morse <james.morse@....com>
> > Date: Thu, 30 Aug 2018 16:05:32 +0100
> > Subject: arm64: mm: always enable CONFIG_HOLES_IN_ZONE
> > 
> > From: James Morse <james.morse@....com>
> > 
> > commit f52bb98f5aded4c43e52f5ce19fb83f7261e9e73 upstream.
> > 
> > Commit 6d526ee26ccd ("arm64: mm: enable CONFIG_HOLES_IN_ZONE for NUMA")
> > only enabled HOLES_IN_ZONE for NUMA systems because the NUMA code was
> > choking on the missing zone for nomap pages. This problem doesn't just
> > apply to NUMA systems.
> > 
> > If the architecture doesn't set HAVE_ARCH_PFN_VALID, pfn_valid() will
> > return true if the pfn is part of a valid sparsemem section.
> > 
> > When working with multiple pages, the mm code uses pfn_valid_within()
> > to test each page it uses within the sparsemem section is valid. On
> > most systems memory comes in MAX_ORDER_NR_PAGES chunks which all
> > have valid/initialised struct pages. In this case pfn_valid_within()
> > is optimised out.
> > 
> > Systems where this isn't true (e.g. due to nomap) should set
> > HOLES_IN_ZONE and provide HAVE_ARCH_PFN_VALID so that mm tests each
> > page as it works with it.
> > 
> > Currently non-NUMA arm64 systems can't enable HOLES_IN_ZONE, leading to
> > a VM_BUG_ON():
> > 
> > | page:fffffdff802e1780 is uninitialized and poisoned
> > | raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
> > | raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
> > | page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
> > | ------------[ cut here ]------------
> > | kernel BUG at include/linux/mm.h:978!
> > | Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
> > [...]
> > | CPU: 1 PID: 25236 Comm: dd Not tainted 4.18.0 #7
> > | Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
> > | pstate: 40000085 (nZcv daIf -PAN -UAO)
> > | pc : move_freepages_block+0x144/0x248
> > | lr : move_freepages_block+0x144/0x248
> > | sp : fffffe0071177680
> > [...]
> > | Process dd (pid: 25236, stack limit = 0x0000000094cc07fb)
> > | Call trace:
> > |  move_freepages_block+0x144/0x248
> > |  steal_suitable_fallback+0x100/0x16c
> > |  get_page_from_freelist+0x440/0xb20
> > |  __alloc_pages_nodemask+0xe8/0x838
> > |  new_slab+0xd4/0x418
> > |  ___slab_alloc.constprop.27+0x380/0x4a8
> > |  __slab_alloc.isra.21.constprop.26+0x24/0x34
> > |  kmem_cache_alloc+0xa8/0x180
> > |  alloc_buffer_head+0x1c/0x90
> > |  alloc_page_buffers+0x68/0xb0
> > |  create_empty_buffers+0x20/0x1ec
> > |  create_page_buffers+0xb0/0xf0
> > |  __block_write_begin_int+0xc4/0x564
> > |  __block_write_begin+0x10/0x18
> > |  block_write_begin+0x48/0xd0
> > |  blkdev_write_begin+0x28/0x30
> > |  generic_perform_write+0x98/0x16c
> > |  __generic_file_write_iter+0x138/0x168
> > |  blkdev_write_iter+0x80/0xf0
> > |  __vfs_write+0xe4/0x10c
> > |  vfs_write+0xb4/0x168
> > |  ksys_write+0x44/0x88
> > |  sys_write+0xc/0x14
> > |  el0_svc_naked+0x30/0x34
> > | Code: aa1303e0 90001a01 91296421 94008902 (d4210000)
> > | ---[ end trace 1601ba47f6e883fe ]---
> > 
> > Remove the NUMA dependency.
> > 
> > Link: https://www.spinics.net/lists/arm-kernel/msg671851.html
> > Cc: <stable@...r.kernel.org>
> > Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> > Reported-by: Mikulas Patocka <mpatocka@...hat.com>
> > Reviewed-by: Pavel Tatashin <pavel.tatashin@...rosoft.com>
> > Tested-by: Mikulas Patocka <mpatocka@...hat.com>
> > Signed-off-by: James Morse <james.morse@....com>
> > Signed-off-by: Will Deacon <will.deacon@....com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > 
> > ---
> >  arch/arm64/Kconfig |    1 -
> >  1 file changed, 1 deletion(-)
> > 
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -631,7 +631,6 @@ config HAVE_SETUP_PER_CPU_AREA
> >  
> >  config NEED_PER_CPU_EMBED_FIRST_CHUNK
> 
> Looks like git got confused here, this isn't HOLES_IN_ZONE.
> 
> Additionally, commit 6d526ee26ccd ("arm64: mm: enable
> CONFIG_HOLES_IN_ZONE for NUMA") that introduced it to this file didn't
> appear until 4.11 so this patch can be dropped from 4.9.

Argh, I thought I had checked that too...

Anyway, thanks for letting me know, I've now dropped it from the 4.9
queue.

greg k-h

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