f2fs: fix up f2fs_lookup tracepoints

Fix up a misuse that the filename pointer isn't always valid in
the ring buffer, and we should copy the content instead.

Fixes: 0c5e36d ("f2fs: trace f2fs_lookup")
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: hsiangkao

include/trace/events/f2fs.h

@@ -807,20 +807,20 @@ TRACE_EVENT(f2fs_lookup_start,
 	TP_STRUCT__entry(
 		__field(dev_t,	dev)
 		__field(ino_t,	ino)
-		__field(const char *,	name)
+		__string(name,	dentry->d_name.name)
 		__field(unsigned int, flags)
 	),
 
 	TP_fast_assign(
 		__entry->dev	= dir->i_sb->s_dev;
 		__entry->ino	= dir->i_ino;
-		__entry->name	= dentry->d_name.name;
+		__assign_str(name, dentry->d_name.name);
 		__entry->flags	= flags;
 	),
 
 	TP_printk("dev = (%d,%d), pino = %lu, name:%s, flags:%u",
 		show_dev_ino(__entry),
-		__entry->name,
+		__get_str(name),
 		__entry->flags)
 );
 
@@ -834,22 +834,22 @@ TRACE_EVENT(f2fs_lookup_end,
 	TP_STRUCT__entry(
 		__field(dev_t,	dev)
 		__field(ino_t,	ino)
-		__field(const char *,	name)
+		__string(name,	dentry->d_name.name)
 		__field(nid_t,	cino)
 		__field(int,	err)
 	),
 
 	TP_fast_assign(
 		__entry->dev	= dir->i_sb->s_dev;
 		__entry->ino	= dir->i_ino;
-		__entry->name	= dentry->d_name.name;
+		__assign_str(name, dentry->d_name.name);
 		__entry->cino	= ino;
 		__entry->err	= err;
 	),
 
 	TP_printk("dev = (%d,%d), pino = %lu, name:%s, ino:%u, err:%d",
 		show_dev_ino(__entry),
-		__entry->name,
+		__get_str(name),
 		__entry->cino,
 		__entry->err)
 );