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@xxxxxxxxxx>
> Signed-off-by: Jane Chu <jane.chu@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
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.
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
>
--
Michal Hocko
SUSE Labs
