On Wed, 21 Mar 2018 09:13:14 -0700 Mike Kravetz mike.kravetz@oracle.com wrote:
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 8<--8<--8<--8< snip 8<--8<--8<--8< 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 GPR00: c00000000036ee48 c000003fbcdcfa90 c0000000016ea600 c000003fbcdcfc40 GPR04: c000003fd9858950 00007115e4e00000 00007115e4e10000 0000000000000000 GPR08: 0000000000000010 0000000000010000 0000000000000000 0000000000000000 GPR12: 0000000000002000 c000000007a2c600 00000fe3985954d0 00007115e4e00000 GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 GPR20: 00000fe398595a94 000000000000a6fc c000003fd9858950 0000000000018554 GPR24: c000003fdcd84500 c0000000019acd00 00007115e4e10000 c000003fbcdcfc40 GPR28: 0000000000200000 00007115e4e00000 c000003fbc9ac600 c000003fd9858950 NIP [c00000000036e764] __unmap_hugepage_range+0xa4/0x760 LR [c00000000036ee48] __unmap_hugepage_range_final+0x28/0x50 Call Trace: [c000003fbcdcfa90] [00007115e4e00000] 0x7115e4e00000 (unreliable) [c000003fbcdcfb50] [c00000000036ee48] __unmap_hugepage_range_final+0x28/0x50 [c000003fbcdcfb80] [c00000000033497c] unmap_single_vma+0x11c/0x190 [c000003fbcdcfbd0] [c000000000334e14] unmap_vmas+0x94/0x140 [c000003fbcdcfc20] [c00000000034265c] exit_mmap+0x9c/0x1d0 [c000003fbcdcfce0] [c000000000105448] mmput+0xa8/0x1d0 [c000003fbcdcfd10] [c00000000010fad0] do_exit+0x360/0xc80 [c000003fbcdcfdd0] [c0000000001104c0] do_group_exit+0x60/0x100 [c000003fbcdcfe10] [c000000000110584] SyS_exit_group+0x24/0x30 [c000003fbcdcfe30] [c00000000000b184] system_call+0x58/0x6c Instruction dump: 552907fe e94a0028 e94a0408 eb2a0018 81590008 7f9c5036 0b090000 e9390010 7d2948f8 7d2a2838 0b0a0000 7d293038 <0b090000> e9230086 2fa90000 419e0468 ---[ 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.
--- a/ipc/shm.c +++ b/ipc/shm.c @@ -386,6 +386,17 @@ static int shm_fault(struct vm_fault *vmf) 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);
This will be the only site which tests for NULL shm_file_data.vm_ops. It's a can't-happen, methinks.
I think I'll leave it as it is for now and will queue up a non-urgent patch:
From: Andrew Morton akpm@linux-foundation.org Subject: ipc/shm.c: shm_split(): remove unneeded test for NULL shm_file_data.vm_ops
This was added by the recent "ipc/shm.c: add split function to shm_vm_ops", but it is not necessary.
Cc: Laurent Dufour ldufour@linux.vnet.ibm.com Cc: Dan Williams dan.j.williams@intel.com Cc: Michal Hocko mhocko@suse.com Cc: Davidlohr Bueso dave@stgolabs.net Cc: Manfred Spraul manfred@colorfullife.com Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
ipc/shm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN ipc/shm.c~ipc-shmc-shm_split-remove-unneeded-test-for-null-shm_file_datavm_ops ipc/shm.c --- a/ipc/shm.c~ipc-shmc-shm_split-remove-unneeded-test-for-null-shm_file_datavm_ops +++ a/ipc/shm.c @@ -391,7 +391,7 @@ static int shm_split(struct vm_area_stru struct file *file = vma->vm_file; struct shm_file_data *sfd = shm_file_data(file);
- if (sfd->vm_ops && sfd->vm_ops->split) + if (sfd->vm_ops->split) return sfd->vm_ops->split(vma, addr);
return 0; _