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Subject[PATCH 4.9 008/102] ipc/shm.c: add split function to shm_vm_ops
4.9-stable review patch.  If anyone has any objections, please let me know.


From: Mike Kravetz <>

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]
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)
---[ 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.

Fixes: 31383c6865a5 ("mm, hugetlbfs: introduce ->split() to vm_operations_struct")
Signed-off-by: Mike Kravetz <>
Reported-by: Laurent Dufour <>
Reviewed-by: Laurent Dufour <>
Tested-by: Laurent Dufour <>
Reviewed-by: Dan Williams <>
Acked-by: Michal Hocko <>
Cc: Davidlohr Bueso <>
Cc: Manfred Spraul <>
Cc: <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Greg Kroah-Hartman <>

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

--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -381,6 +381,17 @@ static int shm_fault(struct vm_area_stru
return sfd->vm_ops->fault(vma, 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;
static int shm_set_policy(struct vm_area_struct *vma, struct mempolicy *new)
@@ -503,6 +514,7 @@ 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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