Re: [PATCH] ipc/shm.c add ->pagesize function to shm_vm_ops

[Mike Kravetz]

On 07/27/2018 02:17 PM, 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.

Thanks Jane!
Adding Dan on Cc as he authored 05ea88608d4e13.  Note that this is the
same type of omission that was made when adding ->split() to
vm_operations_struct. :(  That is why I suggested adding the comment
above vm_operations_struct.

> 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

We will need the tag,
Fixes: 05ea88608d4e13 ("mm, hugetlbfs: introduce ->pagesize() to vm_operations_struct")
and,
CC: stable@xxxxxxxxxxxxxxx

> Suggested-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Signed-off-by: Jane Chu <jane.chu@xxxxxxxxxx>
> ---
>  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,
> 

Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
-- 
Mike Kravetz