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    Subject[PATCH 4.14 13/67] ipc/shm.c: add split function to shm_vm_ops
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Mike Kravetz <mike.kravetz@oracle.com>

    commit 3d942ee079b917b24e2a0c5f18d35ac8ec9fee48 upstream.

    If System V shmget/shmat operations are used to create a hugetlbfs
    backed mapping, it is possible to munmap part of the mapping and split
    the underlying vma such that it is not huge page aligned. This will
    untimately result in the following BUG:

    kernel BUG at /build/linux-jWa1Fv/linux-4.15.0/mm/hugetlb.c:3310!
    Oops: Exception in kernel mode, sig: 5 [#1]
    LE SMP NR_CPUS=2048 NUMA PowerNV
    Modules linked in: kcm nfc af_alg caif_socket caif phonet fcrypt
    CPU: 18 PID: 43243 Comm: trinity-subchil Tainted: G C E 4.15.0-10-generic #11-Ubuntu
    NIP: c00000000036e764 LR: c00000000036ee48 CTR: 0000000000000009
    REGS: c000003fbcdcf810 TRAP: 0700 Tainted: G C E (4.15.0-10-generic)
    MSR: 9000000000029033 <SF,HV,EE,ME,IR,DR,RI,LE> CR: 24002222 XER: 20040000
    CFAR: c00000000036ee44 SOFTE: 1
    NIP __unmap_hugepage_range+0xa4/0x760
    LR __unmap_hugepage_range_final+0x28/0x50
    Call Trace:
    0x7115e4e00000 (unreliable)
    __unmap_hugepage_range_final+0x28/0x50
    unmap_single_vma+0x11c/0x190
    unmap_vmas+0x94/0x140
    exit_mmap+0x9c/0x1d0
    mmput+0xa8/0x1d0
    do_exit+0x360/0xc80
    do_group_exit+0x60/0x100
    SyS_exit_group+0x24/0x30
    system_call+0x58/0x6c
    ---[ end trace ee88f958a1c62605 ]---

    This bug was introduced by commit 31383c6865a5 ("mm, hugetlbfs:
    introduce ->split() to vm_operations_struct"). A split function was
    added to vm_operations_struct to determine if a mapping can be split.
    This was mostly for device-dax and hugetlbfs mappings which have
    specific alignment constraints.

    Mappings initiated via shmget/shmat have their original vm_ops
    overwritten with shm_vm_ops. shm_vm_ops functions will call back to the
    original vm_ops if needed. Add such a split function to shm_vm_ops.

    Link: http://lkml.kernel.org/r/20180321161314.7711-1-mike.kravetz@oracle.com
    Fixes: 31383c6865a5 ("mm, hugetlbfs: introduce ->split() to vm_operations_struct")
    Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
    Reported-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
    Reviewed-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
    Tested-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
    Reviewed-by: Dan Williams <dan.j.williams@intel.com>
    Acked-by: Michal Hocko <mhocko@suse.com>
    Cc: Davidlohr Bueso <dave@stgolabs.net>
    Cc: Manfred Spraul <manfred@colorfullife.com>
    Cc: <stable@vger.kernel.org>
    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>

    ---
    ipc/shm.c | 12 ++++++++++++
    1 file changed, 12 insertions(+)

    --- a/ipc/shm.c
    +++ b/ipc/shm.c
    @@ -386,6 +386,17 @@ static int shm_fault(struct vm_fault *vm
    return sfd->vm_ops->fault(vmf);
    }

    +static int shm_split(struct vm_area_struct *vma, unsigned long addr)
    +{
    + struct file *file = vma->vm_file;
    + struct shm_file_data *sfd = shm_file_data(file);
    +
    + if (sfd->vm_ops && sfd->vm_ops->split)
    + return sfd->vm_ops->split(vma, addr);
    +
    + return 0;
    +}
    +
    #ifdef CONFIG_NUMA
    static int shm_set_policy(struct vm_area_struct *vma, struct mempolicy *new)
    {
    @@ -510,6 +521,7 @@ static const struct vm_operations_struct
    .open = shm_open, /* callback for a new vm-area open */
    .close = shm_close, /* callback for when the vm-area is released */
    .fault = shm_fault,
    + .split = shm_split,
    #if defined(CONFIG_NUMA)
    .set_policy = shm_set_policy,
    .get_policy = shm_get_policy,

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