[f2fs-dev] [PATCH v2 2/4] f2fs: atomic: fix to not allow GC to pollute atomic_file

[Chao Yu <chao@kernel.org>]

SQLite App			GC Thread	Shrinker
- f2fs_ioc_start_atomic_write

- f2fs_ioc_commit_atomic_write
 - f2fs_commit_atomic_write
  - filemap_write_and_wait_range
  : write atomic_file's data to cow_inode
						echo 3 > drop_caches
				- f2fs_gc
				 - gc_data_segment
				  - move_data_page
				   - set_page_dirty
				   : it may load data of previous
				     transaction into pagecache.
  - f2fs_down_write(&fi->i_gc_rwsem[WRITE])
  - __f2fs_commit_atomic_write
  - f2fs_up_write(&fi->i_gc_rwsem[WRITE])

During committing atomic_file, GC may be triggered to migrate
atomic_file's block, so it may contain data of previous transaction
in page cache, we should drop atomic_file's cache once it was
migrated by GC.

And also, we should writeback atomic_file and cow_file's data
w/ i_gc_rwsem lock held, in order to avoid block address change
during __f2fs_commit_atomic_write().

Meahwhile, this patch adds f2fs_wait_on_block_writeback_range()
to wait completion of block migration.

Fixes: 3db1de0e582c ("f2fs: change the current atomic write way")
Signed-off-by: Chao Yu <chao@kernel.org>
---
v2:
- fix error path handling.
 fs/f2fs/segment.c | 27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 3aee71c9f3c6..a43054ab0cf1 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -236,6 +236,9 @@ static int __replace_atomic_write_block(struct inode *inode, pgoff_t index,
 		return err;
 	}
 
+	if (__is_valid_data_blkaddr(dn.data_blkaddr))
+		f2fs_wait_on_block_writeback_range(inode, dn.data_blkaddr, 1);
+
 	if (recover) {
 		/* dn.data_blkaddr is always valid */
 		if (!__is_valid_data_blkaddr(new_addr)) {
@@ -339,6 +342,9 @@ static int __f2fs_commit_atomic_write(struct inode *inode)
 				goto out;
 			}
 
+			f2fs_wait_on_block_writeback_range(cow_inode,
+								blkaddr, 1);
+
 			new = f2fs_kmem_cache_alloc(revoke_entry_slab, GFP_NOFS,
 							true, NULL);
 
@@ -379,16 +385,29 @@ int f2fs_commit_atomic_write(struct inode *inode)
 	struct f2fs_inode_info *fi = F2FS_I(inode);
 	int err;
 
+	f2fs_down_write(&fi->i_gc_rwsem[WRITE]);
+
 	err = filemap_write_and_wait_range(inode->i_mapping, 0, LLONG_MAX);
 	if (err)
-		return err;
+		goto out;
 
-	f2fs_down_write(&fi->i_gc_rwsem[WRITE]);
-	f2fs_lock_op(sbi);
+	/* writeback GCing page of cow_inode */
+	err = filemap_write_and_wait_range(fi->cow_inode->i_mapping,
+							0, LLONG_MAX);
+	if (err)
+		goto out;
 
-	err = __f2fs_commit_atomic_write(inode);
+	filemap_invalidate_lock(inode->i_mapping);
+
+	/* don't allow clean page loaded by GC to pollute atomic_file */
+	truncate_pagecache(inode, 0);
 
+	f2fs_lock_op(sbi);
+	err = __f2fs_commit_atomic_write(inode);
 	f2fs_unlock_op(sbi);
+
+	filemap_invalidate_unlock(inode->i_mapping);
+out:
 	f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
 
 	return err;
-- 
2.40.1



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