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

[Jane Chu]

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@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.

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