[16/18] btrfs: Writeprotect mmap pages on snapshot

Commit Message

Goldwyn Rodrigues April 16, 2019, 4:41 p.m. UTC

From: Goldwyn Rodrigues <[e-mail]>

Inorder to make sure mmap'd files don't change after snapshot,
writeprotect the mmap pages on snapshot. This is done by performing
a data writeback on the pages (which simply mark the pages are
wrprotected). This way if the user process tries to access the memory
we will get another fault and we can perform a CoW.

In order to accomplish this, we tag all CoW pages as
PAGECACHE_TAG_TOWRITE, and add the mmapd inode in delalloc_inodes.
During snapshot, it starts writeback of all delalloc'd inodes and
here we perform a data writeback. We don't want to keep the inodes
in delalloc_inodes until it umount (WARN_ON), so we remove it
during inode evictions.

Signed-off-by: Goldwyn Rodrigues <[e-mail]>
---
 fs/btrfs/ctree.h |  3 ++-
 fs/btrfs/dax.c   |  7 +++++++
 fs/btrfs/inode.c | 13 ++++++++++++-
 3 files changed, 21 insertions(+), 2 deletions(-)

Patch

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index ee1ed18f8b3c..d1b70f24adeb 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3252,7 +3252,8 @@  int btrfs_create_subvol_root(struct btrfs_trans_handle *trans,
 			     struct btrfs_root *new_root,
 			     struct btrfs_root *parent_root,
 			     u64 new_dirid);
- void btrfs_set_delalloc_extent(struct inode *inode, struct extent_state *state,
+void btrfs_add_delalloc_inodes(struct btrfs_root *root, struct inode *inode);
+void btrfs_set_delalloc_extent(struct inode *inode, struct extent_state *state,
 			       unsigned *bits);
 void btrfs_clear_delalloc_extent(struct inode *inode,
 				 struct extent_state *state, unsigned *bits);
diff --git a/fs/btrfs/dax.c b/fs/btrfs/dax.c
index a4b36d5b537c..2740c15286ee 100644
--- a/fs/btrfs/dax.c
+++ b/fs/btrfs/dax.c
@@ -222,10 +222,17 @@  vm_fault_t btrfs_dax_fault(struct vm_fault *vmf)
 {
 	vm_fault_t ret;
 	pfn_t pfn;
+	struct inode *inode = file_inode(vmf->vma->vm_file);
+	struct btrfs_inode *binode = BTRFS_I(inode);
 	ret = dax_iomap_fault(vmf, PE_SIZE_PTE, &pfn, NULL, &btrfs_iomap_ops);
 	if (ret & VM_FAULT_NEEDDSYNC)
 		ret = dax_finish_sync_fault(vmf, PE_SIZE_PTE, pfn);
 
+	/* Insert into delalloc so we get writeback calls on snapshots */
+	if (vmf->flags & FAULT_FLAG_WRITE &&
+			!test_bit(BTRFS_INODE_IN_DELALLOC_LIST, &binode->runtime_flags))
+		btrfs_add_delalloc_inodes(binode->root, inode);
+
 	return ret;
 }
 
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index f6a64607bc8c..d439c6c80a2a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1713,7 +1713,7 @@  void btrfs_merge_delalloc_extent(struct inode *inode, struct extent_state *new,
 	spin_unlock(&BTRFS_I(inode)->lock);
 }
 
-static void btrfs_add_delalloc_inodes(struct btrfs_root *root,
+void btrfs_add_delalloc_inodes(struct btrfs_root *root,
 				      struct inode *inode)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
@@ -5358,12 +5358,17 @@  void btrfs_evict_inode(struct inode *inode)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
 	struct btrfs_trans_handle *trans;
+	struct btrfs_inode *binode = BTRFS_I(inode);
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct btrfs_block_rsv *rsv;
 	int ret;
 
 	trace_btrfs_inode_evict(inode);
 
+	if (IS_DAX(inode)
+	    && test_bit(BTRFS_INODE_IN_DELALLOC_LIST, &binode->runtime_flags))
+		btrfs_del_delalloc_inode(root, binode);
+
 	if (!root) {
 		clear_inode(inode);
 		return;
@@ -8683,6 +8688,10 @@  static int btrfs_dax_writepages(struct address_space *mapping,
 {
 	struct inode *inode = mapping->host;
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	struct btrfs_inode *binode = BTRFS_I(inode);
+	if ((wbc->sync_mode == WB_SYNC_ALL) &&
+	    test_bit(BTRFS_INODE_IN_DELALLOC_LIST, &binode->runtime_flags))
+		btrfs_del_delalloc_inode(binode->root, binode);
 	return dax_writeback_mapping_range(mapping, fs_info->fs_devices->latest_bdev,
 			wbc);
 }
@@ -9981,6 +9990,8 @@  static void btrfs_run_delalloc_work(struct btrfs_work *work)
 	delalloc_work = container_of(work, struct btrfs_delalloc_work,
 				     work);
 	inode = delalloc_work->inode;
+	if (IS_DAX(inode))
+		filemap_fdatawrite(inode->i_mapping);
 	filemap_flush(inode->i_mapping);
 	if (test_bit(BTRFS_INODE_HAS_ASYNC_EXTENT,
 				&BTRFS_I(inode)->runtime_flags))