[PATCH v2] f2fs: refactor ->page_mkwrite() flow

[Chao Yu]

Thread A				Thread B
- f2fs_vm_page_mkwrite
					- f2fs_setattr
					 - down_write(i_mmap_sem)
					 - truncate_setsize
					 - f2fs_truncate
					 - up_write(i_mmap_sem)
 - f2fs_reserve_block
 reserve NEW_ADDR
 - skip dirty page due to truncation

1. we don't need to rserve new block address for a truncated page.
2. dn.data_blkaddr is used out of node page lock coverage.

Refactor ->page_mkwrite() flow to fix above issues:
- use __do_map_lock() to avoid racing checkpoint()
- lock data page in prior to dnode page
- cover f2fs_reserve_block with i_mmap_sem lock
- wait page writeback before zeroing page

Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
v2:
- handle error path correctly
- wait page writeback before zeroing page
 fs/f2fs/data.c |  2 +-
 fs/f2fs/f2fs.h |  1 +
 fs/f2fs/file.c | 45 ++++++++++++++++++++++-----------------------
 3 files changed, 24 insertions(+), 24 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 41102c227eee..b287422c8eeb 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -972,7 +972,7 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
 	return err;
 }
 
-static inline void __do_map_lock(struct f2fs_sb_info *sbi, int flag, bool lock)
+void __do_map_lock(struct f2fs_sb_info *sbi, int flag, bool lock)
 {
 	if (flag == F2FS_GET_BLOCK_PRE_AIO) {
 		if (lock)
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index b32fd9f7da95..8f4a46603c61 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -3050,6 +3050,7 @@ struct page *f2fs_get_lock_data_page(struct inode *inode, pgoff_t index,
 struct page *f2fs_get_new_data_page(struct inode *inode,
 			struct page *ipage, pgoff_t index, bool new_i_size);
 int f2fs_do_write_data_page(struct f2fs_io_info *fio);
+void __do_map_lock(struct f2fs_sb_info *sbi, int flag, bool lock);
 int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map,
 			int create, int flag);
 int f2fs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 357422a4c319..6db808c80813 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -47,7 +47,7 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
 	struct page *page = vmf->page;
 	struct inode *inode = file_inode(vmf->vma->vm_file);
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
-	struct dnode_of_data dn;
+	struct dnode_of_data dn = { .node_changed = false };
 	int err;
 
 	if (unlikely(f2fs_cp_error(sbi))) {
@@ -59,19 +59,6 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
 
 	f2fs_bug_on(sbi, f2fs_has_inline_data(inode));
 
-	/* block allocation */
-	f2fs_lock_op(sbi);
-	set_new_dnode(&dn, inode, NULL, NULL, 0);
-	err = f2fs_reserve_block(&dn, page->index);
-	if (err) {
-		f2fs_unlock_op(sbi);
-		goto out;
-	}
-	f2fs_put_dnode(&dn);
-	f2fs_unlock_op(sbi);
-
-	f2fs_balance_fs(sbi, dn.node_changed);
-
 	file_update_time(vmf->vma->vm_file);
 	down_read(&F2FS_I(inode)->i_mmap_sem);
 	lock_page(page);
@@ -83,11 +70,28 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
 		goto out_sem;
 	}
 
+	/* block allocation */
+	__do_map_lock(sbi, F2FS_GET_BLOCK_PRE_AIO, true);
+	set_new_dnode(&dn, inode, NULL, NULL, 0);
+	err = f2fs_get_block(&dn, page->index);
+	f2fs_put_dnode(&dn);
+	__do_map_lock(sbi, F2FS_GET_BLOCK_PRE_AIO, false);
+	if (err) {
+		unlock_page(page);
+		goto out_sem;
+	}
+
+	/* fill the page */
+	f2fs_wait_on_page_writeback(page, DATA, false);
+
+	/* wait for GCed page writeback via META_MAPPING */
+	f2fs_wait_on_block_writeback(inode, dn.data_blkaddr);
+
 	/*
 	 * check to see if the page is mapped already (no holes)
 	 */
 	if (PageMappedToDisk(page))
-		goto mapped;
+		goto out_sem;
 
 	/* page is wholly or partially inside EOF */
 	if (((loff_t)(page->index + 1) << PAGE_SHIFT) >
@@ -104,16 +108,11 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
 	f2fs_update_iostat(sbi, APP_MAPPED_IO, F2FS_BLKSIZE);
 
 	trace_f2fs_vm_page_mkwrite(page, DATA);
-mapped:
-	/* fill the page */
-	f2fs_wait_on_page_writeback(page, DATA, false);
-
-	/* wait for GCed page writeback via META_MAPPING */
-	f2fs_wait_on_block_writeback(inode, dn.data_blkaddr);
-
 out_sem:
 	up_read(&F2FS_I(inode)->i_mmap_sem);
-out:
+
+	f2fs_balance_fs(sbi, dn.node_changed);
+
 	sb_end_pagefault(inode->i_sb);
 	f2fs_update_time(sbi, REQ_TIME);
 err:
-- 
2.18.0.rc1