On Wed, Jun 29, 2022 at 04:53:58PM -0600, Khalid Aziz wrote: > Number of mappings of an mshare region should be tracked so it can > be removed when there are no more references to it and associated > file has been deleted. This add code to support the unlink operation > for associated file, remove the mshare region on file deletion if > refcount goes to zero, add munmap operation to maintain refcount > to mshare region and remove it on last munmap if file has been > deleted. > > Signed-off-by: Khalid Aziz <khalid.aziz@xxxxxxxxxx> > --- > mm/mshare.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 63 insertions(+), 1 deletion(-) > > diff --git a/mm/mshare.c b/mm/mshare.c > index 088a6cab1e93..90ce0564a138 100644 > --- a/mm/mshare.c > +++ b/mm/mshare.c > @@ -29,6 +29,7 @@ static struct super_block *msharefs_sb; > struct mshare_data { > struct mm_struct *mm; > refcount_t refcnt; > + int deleted; > struct mshare_info *minfo; > }; > > @@ -48,6 +49,7 @@ msharefs_read(struct kiocb *iocb, struct iov_iter *iov) > size_t ret; > struct mshare_info m_info; > > + mmap_read_lock(info->mm); > if (info->minfo != NULL) { > m_info.start = info->minfo->start; > m_info.size = info->minfo->size; > @@ -55,18 +57,42 @@ msharefs_read(struct kiocb *iocb, struct iov_iter *iov) > m_info.start = 0; > m_info.size = 0; > } > + mmap_read_unlock(info->mm); > ret = copy_to_iter(&m_info, sizeof(m_info), iov); > if (!ret) > return -EFAULT; > return ret; > } > > +static void > +msharefs_close(struct vm_area_struct *vma) > +{ > + struct mshare_data *info = vma->vm_private_data; > + > + if (refcount_dec_and_test(&info->refcnt)) { > + mmap_read_lock(info->mm); > + if (info->deleted) { > + mmap_read_unlock(info->mm); > + mmput(info->mm); > + kfree(info->minfo); > + kfree(info); Aren't filesystems supposed to take care of disposing of the file data in destroy_inode? IIRC struct inode doesn't go away until all fds are closed, mappings are torn down, and there are no more references from dentries. I could be misremembering since it's been a few months since I went looking at the (VFS) inode lifecycle. > + } else { > + mmap_read_unlock(info->mm); > + } > + } > +} > + > +static const struct vm_operations_struct msharefs_vm_ops = { > + .close = msharefs_close, > +}; > + > static int > msharefs_mmap(struct file *file, struct vm_area_struct *vma) > { > struct mshare_data *info = file->private_data; > struct mm_struct *mm = info->mm; > > + mmap_write_lock(mm); > /* > * If this mshare region has been set up once already, bail out > */ > @@ -80,10 +106,14 @@ msharefs_mmap(struct file *file, struct vm_area_struct *vma) > mm->task_size = vma->vm_end - vma->vm_start; > if (!mm->task_size) > mm->task_size--; > + mmap_write_unlock(mm); > info->minfo->start = mm->mmap_base; > info->minfo->size = mm->task_size; > + info->deleted = 0; > + refcount_inc(&info->refcnt); > vma->vm_flags |= VM_SHARED_PT; > vma->vm_private_data = info; > + vma->vm_ops = &msharefs_vm_ops; > return 0; > } > > @@ -240,6 +270,38 @@ msharefs_mkdir(struct user_namespace *mnt_userns, struct inode *dir, > return ret; > } > > +static int > +msharefs_unlink(struct inode *dir, struct dentry *dentry) > +{ > + struct inode *inode = d_inode(dentry); > + struct mshare_data *info = inode->i_private; > + > + /* > + * Unmap the mshare region if it is still mapped in > + */ > + vm_munmap(info->minfo->start, info->minfo->size); > + > + /* > + * Mark msharefs file for deletion so it can not be opened > + * and used for mshare mappings any more > + */ > + simple_unlink(dir, dentry); > + mmap_write_lock(info->mm); > + info->deleted = 1; > + mmap_write_unlock(info->mm); What if the file is hardlinked? --D > + > + /* > + * Is this the last reference? If so, delete mshare region and > + * remove the file > + */ > + if (!refcount_dec_and_test(&info->refcnt)) { > + mmput(info->mm); > + kfree(info->minfo); > + kfree(info); > + } > + return 0; > +} > + > static const struct inode_operations msharefs_file_inode_ops = { > .setattr = simple_setattr, > .getattr = simple_getattr, > @@ -248,7 +310,7 @@ static const struct inode_operations msharefs_dir_inode_ops = { > .create = msharefs_create, > .lookup = simple_lookup, > .link = simple_link, > - .unlink = simple_unlink, > + .unlink = msharefs_unlink, > .mkdir = msharefs_mkdir, > .rmdir = simple_rmdir, > .mknod = msharefs_mknod, > -- > 2.32.0 >