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SubjectRe: [PATCH] ipc/shm.c add ->pagesize function to shm_vm_ops
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Hi, Michal,


On 7/30/2018 1:58 AM, Michal Hocko wrote:
> On Fri 27-07-18 15:17:27, Jane Chu wrote:
>> Commit 05ea88608d4e13 (mm, hugetlbfs: introduce ->pagesize() to
>> vm_operations_struct) adds a new ->pagesize() function to
>> hugetlb_vm_ops, intended to cover all hugetlbfs backed files.
>>
>> With System V shared memory model, if "huge page" is specified,
>> the "shared memory" is backed by hugetlbfs files, but the mappings
>> initiated via shmget/shmat have their original vm_ops overwritten
>> with shm_vm_ops, so we need to add a ->pagesize function to shm_vm_ops.
>> Otherwise, vma_kernel_pagesize() returns PAGE_SIZE given a hugetlbfs
>> backed vma, result in below BUG:
>>
>> fs/hugetlbfs/inode.c
>> 443 if (unlikely(page_mapped(page))) {
>> 444 BUG_ON(truncate_op);
>>
>> [ 242.268342] hugetlbfs: oracle (4592): Using mlock ulimits for SHM_HUGETLB is deprecated
>> [ 282.653208] ------------[ cut here ]------------
>> [ 282.708447] kernel BUG at fs/hugetlbfs/inode.c:444!
>> [ 282.818957] Modules linked in: nfsv3 rpcsec_gss_krb5 nfsv4 ...
>> [ 284.025873] CPU: 35 PID: 5583 Comm: oracle_5583_sbt Not tainted 4.14.35-1829.el7uek.x86_64 #2
>> [ 284.246609] task: ffff9bf0507aaf80 task.stack: ffffa9e625628000
>> [ 284.317455] RIP: 0010:remove_inode_hugepages+0x3db/0x3e2
>> ....
>> [ 285.292389] Call Trace:
>> [ 285.321630] hugetlbfs_evict_inode+0x1e/0x3e
>> [ 285.372707] evict+0xdb/0x1af
>> [ 285.408185] iput+0x1a2/0x1f7
>> [ 285.443661] dentry_unlink_inode+0xc6/0xf0
>> [ 285.492661] __dentry_kill+0xd8/0x18d
>> [ 285.536459] dput+0x1b5/0x1ed
>> [ 285.571939] __fput+0x18b/0x216
>> [ 285.609495] ____fput+0xe/0x10
>> [ 285.646030] task_work_run+0x90/0xa7
>> [ 285.688788] exit_to_usermode_loop+0xdd/0x116
>> [ 285.740905] do_syscall_64+0x187/0x1ae
>> [ 285.785740] entry_SYSCALL_64_after_hwframe+0x150/0x0
>>
>> Suggested-by: Mike Kravetz <mike.kravetz@oracle.com>
>> Signed-off-by: Jane Chu <jane.chu@oracle.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
>
> with Cc: stable and Fixes: tag as suggested by Mike.
>
> I also agree with Matthew that the comment should be associated with
> hugetlb_vm_ops/shm_vm_ops.

Indeed, will make the above changes.
Thanks for reviewing!

-jane

>
> Thanks!
>
>> ---
>> include/linux/mm.h | 7 +++++++
>> ipc/shm.c | 12 ++++++++++++
>> 2 files changed, 19 insertions(+)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index a0fbb9ffe380..0c759379f2d9 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -387,6 +387,13 @@ enum page_entry_size {
>> * These are the virtual MM functions - opening of an area, closing and
>> * unmapping it (needed to keep files on disk up-to-date etc), pointer
>> * to the functions called when a no-page or a wp-page exception occurs.
>> + *
>> + * Note, when a new function is introduced to vm_operations_struct and
>> + * added to hugetlb_vm_ops, please consider adding the function to
>> + * shm_vm_ops. This is because under System V memory model, though
>> + * mappings created via shmget/shmat with "huge page" specified are
>> + * backed by hugetlbfs files, their original vm_ops are overwritten with
>> + * shm_vm_ops.
>> */
>> struct vm_operations_struct {
>> void (*open)(struct vm_area_struct * area);
>> diff --git a/ipc/shm.c b/ipc/shm.c
>> index 051a3e1fb8df..fefa00d310fb 100644
>> --- a/ipc/shm.c
>> +++ b/ipc/shm.c
>> @@ -427,6 +427,17 @@ static int shm_split(struct vm_area_struct *vma, unsigned long addr)
>> return 0;
>> }
>>
>> +static unsigned long shm_pagesize(struct vm_area_struct *vma)
>> +{
>> + struct file *file = vma->vm_file;
>> + struct shm_file_data *sfd = shm_file_data(file);
>> +
>> + if (sfd->vm_ops->pagesize)
>> + return sfd->vm_ops->pagesize(vma);
>> +
>> + return PAGE_SIZE;
>> +}
>> +
>> #ifdef CONFIG_NUMA
>> static int shm_set_policy(struct vm_area_struct *vma, struct mempolicy *new)
>> {
>> @@ -554,6 +565,7 @@ static const struct vm_operations_struct shm_vm_ops = {
>> .close = shm_close, /* callback for when the vm-area is released */
>> .fault = shm_fault,
>> .split = shm_split,
>> + .pagesize = shm_pagesize,
>> #if defined(CONFIG_NUMA)
>> .set_policy = shm_set_policy,
>> .get_policy = shm_get_policy,
>> --
>> 2.15.GIT
>>

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