Messages in this thread | | | Subject | Re: [PATCH v2] mm/ksm: ignore STABLE_FLAG of rmap_item->address in rmap_walk_ksm | From | Suzuki K Poulose <> | Date | Mon, 14 May 2018 10:09:47 +0100 |
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On 10/05/18 02:26, Jia He wrote: > Hi Andrew > > > On 5/10/2018 7:31 AM, Andrew Morton Wrote: >> On Fri, 4 May 2018 11:11:46 +0800 Jia He <hejianet@gmail.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@hxt-semitech.com >> I assumed you wanted this patch to be committed as >> From:jia.he@hxt-semitech.com rather than From:hejianet@gmail.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
> [35380.908341] 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
Please could you share your "changes" (that injected the fault) that triggered this Panic and the steps that triggered this ?
The only reason we should get there is by trying to put a page that is not owned by the KVM Stage 2 page table either:
1) It was free'd already ? - We has some race conditions there which were fixed. 2) The code tries to access something that doesn't belong there. - If this happens that doesn't look good for a simple change you mentioned. So we would like to know better about the situation to see if there is something we need to address.
Suzuki
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