f2fs: cover last_disk_size update with spinlock

This change solves below hangtask issue:

INFO: task kworker/u16:1:58 blocked for more than 122 seconds.
      Not tainted 5.6.0-rc2-00590-g9983bdae4974e #11
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u16:1   D    0    58      2 0x00000000
Workqueue: writeback wb_workfn (flush-179:0)
Backtrace:
 (__schedule) from [<c0913234>] (schedule+0x78/0xf4)
 (schedule) from [<c017ec74>] (rwsem_down_write_slowpath+0x24c/0x4c0)
 (rwsem_down_write_slowpath) from [<c0915f2c>] (down_write+0x6c/0x70)
 (down_write) from [<c0435b80>] (f2fs_write_single_data_page+0x608/0x7ac)
 (f2fs_write_single_data_page) from [<c0435fd8>] (f2fs_write_cache_pages+0x2b4/0x7c4)
 (f2fs_write_cache_pages) from [<c043682c>] (f2fs_write_data_pages+0x344/0x35c)
 (f2fs_write_data_pages) from [<c0267ee8>] (do_writepages+0x3c/0xd4)
 (do_writepages) from [<c0310cbc>] (__writeback_single_inode+0x44/0x454)
 (__writeback_single_inode) from [<c03112d0>] (writeback_sb_inodes+0x204/0x4b0)
 (writeback_sb_inodes) from [<c03115cc>] (__writeback_inodes_wb+0x50/0xe4)
 (__writeback_inodes_wb) from [<c03118f4>] (wb_writeback+0x294/0x338)
 (wb_writeback) from [<c0312dac>] (wb_workfn+0x35c/0x54c)
 (wb_workfn) from [<c014f2b8>] (process_one_work+0x214/0x544)
 (process_one_work) from [<c014f634>] (worker_thread+0x4c/0x574)
 (worker_thread) from [<c01564fc>] (kthread+0x144/0x170)
 (kthread) from [<c01010e8>] (ret_from_fork+0x14/0x2c)

Reported-and-tested-by: Ondřej Jirman <megi@xff.cz>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/compress.c

@@ -898,10 +898,10 @@ unlock_continue:
 	f2fs_put_dnode(&dn);
 	f2fs_unlock_op(sbi);
 
-	down_write(&fi->i_sem);
+	spin_lock(&fi->i_size_lock);
 	if (fi->last_disk_size < psize)
 		fi->last_disk_size = psize;
-	up_write(&fi->i_sem);
+	spin_unlock(&fi->i_size_lock);
 
 	f2fs_put_rpages(cc);
 	f2fs_destroy_compress_ctx(cc);

fs/f2fs/data.c

@@ -2647,10 +2647,10 @@ write:
 	if (err) {
 		file_set_keep_isize(inode);
 	} else {
-		down_write(&F2FS_I(inode)->i_sem);
+		spin_lock(&F2FS_I(inode)->i_size_lock);
 		if (F2FS_I(inode)->last_disk_size < psize)
 			F2FS_I(inode)->last_disk_size = psize;
-		up_write(&F2FS_I(inode)->i_sem);
+		spin_unlock(&F2FS_I(inode)->i_size_lock);
 	}
 
 done:

fs/f2fs/f2fs.h

@@ -696,6 +696,7 @@ struct f2fs_inode_info {
 	struct task_struct *cp_task;	/* separate cp/wb IO stats*/
 	nid_t i_xattr_nid;		/* node id that contains xattrs */
 	loff_t	last_disk_size;		/* lastly written file size */
+	spinlock_t i_size_lock;		/* protect last_disk_size */
 
 #ifdef CONFIG_QUOTA
 	struct dquot *i_dquot[MAXQUOTAS];
@@ -2855,9 +2856,9 @@ static inline bool f2fs_skip_inode_update(struct inode *inode, int dsync)
 	if (!f2fs_is_time_consistent(inode))
 		return false;
 
-	down_read(&F2FS_I(inode)->i_sem);
+	spin_lock(&F2FS_I(inode)->i_size_lock);
 	ret = F2FS_I(inode)->last_disk_size == i_size_read(inode);
-	up_read(&F2FS_I(inode)->i_sem);
+	spin_unlock(&F2FS_I(inode)->i_size_lock);
 
 	return ret;
 }

fs/f2fs/file.c

@@ -929,10 +929,10 @@ int f2fs_setattr(struct dentry *dentry, struct iattr *attr)
 		if (err)
 			return err;
 
-		down_write(&F2FS_I(inode)->i_sem);
+		spin_lock(&F2FS_I(inode)->i_size_lock);
 		inode->i_mtime = inode->i_ctime = current_time(inode);
 		F2FS_I(inode)->last_disk_size = i_size_read(inode);
-		up_write(&F2FS_I(inode)->i_sem);
+		spin_unlock(&F2FS_I(inode)->i_size_lock);
 	}
 
 	__setattr_copy(inode, attr);

fs/f2fs/super.c

@@ -960,6 +960,7 @@ static struct inode *f2fs_alloc_inode(struct super_block *sb)
 	/* Initialize f2fs-specific inode info */
 	atomic_set(&fi->dirty_pages, 0);
 	init_rwsem(&fi->i_sem);
+	spin_lock_init(&fi->i_size_lock);
 	INIT_LIST_HEAD(&fi->dirty_list);
 	INIT_LIST_HEAD(&fi->gdirty_list);
 	INIT_LIST_HEAD(&fi->inmem_ilist);