Date:   Thu, 10 May 2018 09:26:24 +0800
From:   Jia He <hejianet@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        Minchan Kim <minchan@...nel.org>,
        Claudio Imbrenda <imbrenda@...ux.vnet.ibm.com>,
        Arvind Yadav <arvind.yadav.cs@...il.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, jia.he@...-semitech.com,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v2] mm/ksm: ignore STABLE_FLAG of rmap_item->address in
 rmap_walk_ksm

Hi Andrew


On 5/10/2018 7:31 AM, Andrew Morton Wrote:
> On Fri,  4 May 2018 11:11:46 +0800 Jia He <hejianet@...il.com> wrote:
>
>> In our armv8a server(QDF2400), I noticed lots of WARN_ON caused by PAGE_SIZE
>> unaligned for rmap_item->address under memory pressure tests(start 20 guests
>> and run memhog in the host).
>>
>> ...
>>
>> In rmap_walk_ksm, the rmap_item->address might still have the STABLE_FLAG,
>> then the start and end in handle_hva_to_gpa might not be PAGE_SIZE aligned.
>> Thus it will cause exceptions in handle_hva_to_gpa on arm64.
>>
>> This patch fixes it by ignoring(not removing) the low bits of address when
>> doing rmap_walk_ksm.
>>
>> Signed-off-by: jia.he@...-semitech.com
> I assumed you wanted this patch to be committed as
> From:jia.he@...-semitech.com rather than From:hejianet@...il.com, so I
> made that change.  Please let me know if this was inappropriate.
Thanks, because there is still some issues in our company's mail server.
I have to use my gmail mailbox.
>
> You can do this yourself by adding an explicit From: line to the very
> start of the patch's email text.
>
> Also, a storm of WARN_ONs is pretty poor behaviour.  Is that the only
> misbehaviour which this bug causes?  Do you think the fix should be
> backported into earlier kernels?
IMO, it should be backported to stable tree, seems that I missed CC to stable 
tree ;-)
the stom of WARN_ONs is very easy for me to reproduce.
More than that, I watched a panic (not reproducible) as follows:
[35380.805825] page:ffff7fe003742d80 count:-4871 mapcount:-2126053375 
mapping:          (null) index:0x0
[35380.815024] flags: 0x1fffc00000000000()
[35380.818845] raw: 1fffc00000000000 0000000000000000 0000000000000000 
ffffecf981470000
[35380.826569] raw: dead000000000100 dead000000000200 ffff8017c001c000 
0000000000000000
[35380.834294] page dumped because: nonzero _refcount
[35380.839069] Modules linked in: vhost_net vhost tap ebtable_filter ebtables 
ip6table_filter ip6_tables iptable_filter fcoe libfcoe libfc 8021q garp mrp stp 
llc scsi_transport_fc openvswitch nf_conntrack_ipv6 nf_nat_ipv6 
nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_defrag_ipv6 nf_nat nf_conntrack 
vfat fat rpcrdma ib_isert iscsi_target_mod ib_iser libiscsi scsi_transport_iscsi 
ib_srpt target_core_mod ib_srp scsi_transport_srp ib_ipoib rdma_ucm ib_ucm 
ib_uverbs ib_umad rdma_cm ib_cm iw_cm mlx5_ib ib_core crc32_ce ipmi_ssif tpm_tis 
tpm_tis_core sg nfsd auth_rpcgss nfs_acl lockd grace sunrpc dm_multipath 
ip_tables xfs libcrc32c mlx5_core mlxfw devlink ahci_platform libahci_platform 
libahci qcom_emac sdhci_acpi sdhci hdma mmc_core hdma_mgmt i2c_qup dm_mirror 
dm_region_hash dm_log dm_mod
[35380.908341] CPU: 29 PID: 18323 Comm: qemu-kvm Tainted: G W       
4.14.15-5.hxt.aarch64 #1
[35380.917107] Hardware name: <snip for confidential issues>
[35380.930909] Call trace:
[35380.933345] [<ffff000008088f00>] dump_backtrace+0x0/0x22c
[35380.938723] [<ffff000008089150>] show_stack+0x24/0x2c
[35380.943759] [<ffff00000893c078>] dump_stack+0x8c/0xb0
[35380.948794] [<ffff00000820ab50>] bad_page+0xf4/0x154
[35380.953740] [<ffff000008211ce8>] free_pages_check_bad+0x90/0x9c
[35380.959642] [<ffff00000820c430>] free_pcppages_bulk+0x464/0x518
[35380.965545] [<ffff00000820db98>] free_hot_cold_page+0x22c/0x300
[35380.971448] [<ffff0000082176fc>] __put_page+0x54/0x60
[35380.976484] [<ffff0000080b1164>] unmap_stage2_range+0x170/0x2b4
[35380.982385] [<ffff0000080b12d8>] kvm_unmap_hva_handler+0x30/0x40
[35380.988375] [<ffff0000080b0104>] handle_hva_to_gpa+0xb0/0xec
[35380.994016] [<ffff0000080b2644>] kvm_unmap_hva_range+0x5c/0xd0
[35380.999833] [<ffff0000080a8054>] 
kvm_mmu_notifier_invalidate_range_start+0x60/0xb0
[35381.007387] [<ffff000008271f44>] __mmu_notifier_invalidate_range_start+0x64/0x8c
[35381.014765] [<ffff0000082547c8>] try_to_unmap_one+0x78c/0x7a4
[35381.020493] [<ffff000008276d04>] rmap_walk_ksm+0x124/0x1a0
[35381.025961] [<ffff0000082551b4>] rmap_walk+0x94/0x98
[35381.030909] [<ffff0000082555e4>] try_to_unmap+0x100/0x124
[35381.036293] [<ffff00000828243c>] unmap_and_move+0x480/0x6fc
[35381.041847] [<ffff000008282b6c>] migrate_pages+0x10c/0x288
[35381.047318] [<ffff00000823c164>] compact_zone+0x238/0x954
[35381.052697] [<ffff00000823c944>] compact_zone_order+0xc4/0xe8
[35381.058427] [<ffff00000823d25c>] try_to_compact_pages+0x160/0x294
[35381.064503] [<ffff00000820f074>] __alloc_pages_direct_compact+0x68/0x194
[35381.071187] [<ffff000008210138>] __alloc_pages_nodemask+0xc20/0xf7c
[35381.077437] [<ffff0000082709e4>] alloc_pages_vma+0x1a4/0x1c0
[35381.083080] [<ffff000008285b68>] do_huge_pmd_anonymous_page+0x128/0x324
[35381.089677] [<ffff000008248a24>] __handle_mm_fault+0x71c/0x7e8
[35381.095492] [<ffff000008248be8>] handle_mm_fault+0xf8/0x194
[35381.101049] [<ffff000008240dcc>] __get_user_pages+0x124/0x34c
[35381.106777] [<ffff000008241870>] populate_vma_page_range+0x90/0x9c
[35381.112941] [<ffff000008241940>] __mm_populate+0xc4/0x15c
[35381.118322] [<ffff00000824b294>] SyS_mlockall+0x100/0x164
[35381.123705] Exception stack(0xffff800dce5f3ec0 to 0xffff800dce5f4000)
[35381.130128] 3ec0: 0000000000000003 d6e6024cc9b87e00 0000aaaabe94f000 
0000000000000000
[35381.137940] 3ee0: 0000000000000002 0000000000000000 0000000000000000 
0000aaaacf6fc3c0
[35381.145753] 3f00: 00000000000000e6 0000aaaacf6fc490 0000ffffeeeab0f0 
d6e6024cc9b87e00
[35381.153565] 3f20: 0000000000000000 0000aaaabe81b3c0 0000000000000020 
00009e53eff806b5
[35381.161379] 3f40: 0000aaaabe94de48 0000ffffa7c269b0 0000000000000011 
0000ffffeeeabf68
[35381.169190] 3f60: 0000aaaaceacfe60 0000aaaabe94f000 0000aaaabe9ba358 
0000aaaabe7ffb80
[35381.177003] 3f80: 0000aaaabe9ba000 0000aaaabe959f64 0000000000000000 
0000aaaabe94f000
[35381.184815] 3fa0: 0000000000000000 0000ffffeeeabdb0 0000aaaabe5f3bf8 
0000ffffeeeabdb0
[35381.192628] 3fc0: 0000ffffa7c269b8 0000000060000000 0000000000000003 
00000000000000e6
[35381.200440] 3fe0: 0000000000000000 0000000000000000 0000000000000000 
0000000000000000
[35381.208254] [<ffff00000808339c>] __sys_trace_return+0x0/0x4
[35381.213809] Disabling lock debugging due to kernel taint

I ever injected a fault on purpose in kvm_unmap_hva_range by set 
size=size-0x200, the call trace is similar
as above. Thus, I thought the panic is similarly caused by the root cause of WARN_ON

-- 
Cheers,
Jia

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