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    Subject[PATCH 5.10 110/145] x86/mm: Fix leak of pmd ptlock
    Date
    From: Dan Williams <dan.j.williams@intel.com>

    commit d1c5246e08eb64991001d97a3bd119c93edbc79a upstream.

    Commit

    28ee90fe6048 ("x86/mm: implement free pmd/pte page interfaces")

    introduced a new location where a pmd was released, but neglected to
    run the pmd page destructor. In fact, this happened previously for a
    different pmd release path and was fixed by commit:

    c283610e44ec ("x86, mm: do not leak page->ptl for pmd page tables").

    This issue was hidden until recently because the failure mode is silent,
    but commit:

    b2b29d6d0119 ("mm: account PMD tables like PTE tables")

    turns the failure mode into this signature:

    BUG: Bad page state in process lt-pmem-ns pfn:15943d
    page:000000007262ed7b refcount:0 mapcount:-1024 mapping:0000000000000000 index:0x0 pfn:0x15943d
    flags: 0xaffff800000000()
    raw: 00affff800000000 dead000000000100 0000000000000000 0000000000000000
    raw: 0000000000000000 ffff913a029bcc08 00000000fffffbff 0000000000000000
    page dumped because: nonzero mapcount
    [..]
    dump_stack+0x8b/0xb0
    bad_page.cold+0x63/0x94
    free_pcp_prepare+0x224/0x270
    free_unref_page+0x18/0xd0
    pud_free_pmd_page+0x146/0x160
    ioremap_pud_range+0xe3/0x350
    ioremap_page_range+0x108/0x160
    __ioremap_caller.constprop.0+0x174/0x2b0
    ? memremap+0x7a/0x110
    memremap+0x7a/0x110
    devm_memremap+0x53/0xa0
    pmem_attach_disk+0x4ed/0x530 [nd_pmem]
    ? __devm_release_region+0x52/0x80
    nvdimm_bus_probe+0x85/0x210 [libnvdimm]

    Given this is a repeat occurrence it seemed prudent to look for other
    places where this destructor might be missing and whether a better
    helper is needed. try_to_free_pmd_page() looks like a candidate, but
    testing with setting up and tearing down pmd mappings via the dax unit
    tests is thus far not triggering the failure.

    As for a better helper pmd_free() is close, but it is a messy fit
    due to requiring an @mm arg. Also, ___pmd_free_tlb() wants to call
    paravirt_tlb_remove_table() instead of free_page(), so open-coded
    pgtable_pmd_page_dtor() seems the best way forward for now.

    Debugged together with Matthew Wilcox <willy@infradead.org>.

    Fixes: 28ee90fe6048 ("x86/mm: implement free pmd/pte page interfaces")
    Signed-off-by: Dan Williams <dan.j.williams@intel.com>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Tested-by: Yi Zhang <yi.zhang@redhat.com>
    Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: <stable@vger.kernel.org>
    Link: https://lkml.kernel.org/r/160697689204.605323.17629854984697045602.stgit@dwillia2-desk3.amr.corp.intel.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/mm/pgtable.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/arch/x86/mm/pgtable.c
    +++ b/arch/x86/mm/pgtable.c
    @@ -829,6 +829,8 @@ int pud_free_pmd_page(pud_t *pud, unsign
    }

    free_page((unsigned long)pmd_sv);
    +
    + pgtable_pmd_page_dtor(virt_to_page(pmd));
    free_page((unsigned long)pmd);

    return 1;

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