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    Subject[PATCH 3.18 112/124] mm, hugetlb: use pte_present() instead of pmd_present() in follow_huge_pmd()
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

    commit c9d398fa237882ea07167e23bcfc5e6847066518 upstream.

    I found the race condition which triggers the following bug when
    move_pages() and soft offline are called on a single hugetlb page
    concurrently.

    Soft offlining page 0x119400 at 0x700000000000
    BUG: unable to handle kernel paging request at ffffea0011943820
    IP: follow_huge_pmd+0x143/0x190
    PGD 7ffd2067
    PUD 7ffd1067
    PMD 0
    [61163.582052] Oops: 0000 [#1] SMP
    Modules linked in: binfmt_misc ppdev virtio_balloon parport_pc pcspkr i2c_piix4 parport i2c_core acpi_cpufreq ip_tables xfs libcrc32c ata_generic pata_acpi virtio_blk 8139too crc32c_intel ata_piix serio_raw libata virtio_pci 8139cp virtio_ring virtio mii floppy dm_mirror dm_region_hash dm_log dm_mod [last unloaded: cap_check]
    CPU: 0 PID: 22573 Comm: iterate_numa_mo Tainted: P OE 4.11.0-rc2-mm1+ #2
    Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
    RIP: 0010:follow_huge_pmd+0x143/0x190
    RSP: 0018:ffffc90004bdbcd0 EFLAGS: 00010202
    RAX: 0000000465003e80 RBX: ffffea0004e34d30 RCX: 00003ffffffff000
    RDX: 0000000011943800 RSI: 0000000000080001 RDI: 0000000465003e80
    RBP: ffffc90004bdbd18 R08: 0000000000000000 R09: ffff880138d34000
    R10: ffffea0004650000 R11: 0000000000c363b0 R12: ffffea0011943800
    R13: ffff8801b8d34000 R14: ffffea0000000000 R15: 000077ff80000000
    FS: 00007fc977710740(0000) GS:ffff88007dc00000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: ffffea0011943820 CR3: 000000007a746000 CR4: 00000000001406f0
    Call Trace:
    follow_page_mask+0x270/0x550
    SYSC_move_pages+0x4ea/0x8f0
    SyS_move_pages+0xe/0x10
    do_syscall_64+0x67/0x180
    entry_SYSCALL64_slow_path+0x25/0x25
    RIP: 0033:0x7fc976e03949
    RSP: 002b:00007ffe72221d88 EFLAGS: 00000246 ORIG_RAX: 0000000000000117
    RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fc976e03949
    RDX: 0000000000c22390 RSI: 0000000000001400 RDI: 0000000000005827
    RBP: 00007ffe72221e00 R08: 0000000000c2c3a0 R09: 0000000000000004
    R10: 0000000000c363b0 R11: 0000000000000246 R12: 0000000000400650
    R13: 00007ffe72221ee0 R14: 0000000000000000 R15: 0000000000000000
    Code: 81 e4 ff ff 1f 00 48 21 c2 49 c1 ec 0c 48 c1 ea 0c 4c 01 e2 49 bc 00 00 00 00 00 ea ff ff 48 c1 e2 06 49 01 d4 f6 45 bc 04 74 90 <49> 8b 7c 24 20 40 f6 c7 01 75 2b 4c 89 e7 8b 47 1c 85 c0 7e 2a
    RIP: follow_huge_pmd+0x143/0x190 RSP: ffffc90004bdbcd0
    CR2: ffffea0011943820
    ---[ end trace e4f81353a2d23232 ]---
    Kernel panic - not syncing: Fatal exception
    Kernel Offset: disabled

    This bug is triggered when pmd_present() returns true for non-present
    hugetlb, so fixing the present check in follow_huge_pmd() prevents it.
    Using pmd_present() to determine present/non-present for hugetlb is not
    correct, because pmd_present() checks multiple bits (not only
    _PAGE_PRESENT) for historical reason and it can misjudge hugetlb state.

    Fixes: e66f17ff7177 ("mm/hugetlb: take page table lock in follow_huge_pmd()")
    Link: http://lkml.kernel.org/r/1490149898-20231-1-git-send-email-n-horiguchi@ah.jp.nec.com
    Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
    Cc: Mike Kravetz <mike.kravetz@oracle.com>
    Cc: Christian Borntraeger <borntraeger@de.ibm.com>
    Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    mm/hugetlb.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    --- a/mm/hugetlb.c
    +++ b/mm/hugetlb.c
    @@ -3753,6 +3753,7 @@ follow_huge_pmd(struct mm_struct *mm, un
    {
    struct page *page = NULL;
    spinlock_t *ptl;
    + pte_t pte;
    retry:
    ptl = pmd_lockptr(mm, pmd);
    spin_lock(ptl);
    @@ -3762,13 +3763,14 @@ retry:
    */
    if (!pmd_huge(*pmd))
    goto out;
    - if (pmd_present(*pmd)) {
    + pte = huge_ptep_get((pte_t *)pmd);
    + if (pte_present(pte)) {
    page = pte_page(*(pte_t *)pmd) +
    ((address & ~PMD_MASK) >> PAGE_SHIFT);
    if (flags & FOLL_GET)
    get_page(page);
    } else {
    - if (is_hugetlb_entry_migration(huge_ptep_get((pte_t *)pmd))) {
    + if (is_hugetlb_entry_migration(pte)) {
    spin_unlock(ptl);
    __migration_entry_wait(mm, (pte_t *)pmd, ptl);
    goto retry;

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