[PATCH v2 7/9] mm/mshare: Add unlink and munmap support

[Khalid Aziz]

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);
+		} 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);
+
+	/*
+	 * 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