linux-kernel - [RFC] f2fs: fix a race condition between evict & gc

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Date:	Mon, 16 May 2016 10:40:21 +0000
From:	Hou Pengyang <houpengyang@...wei.com>
To:	<jaegeuk@...nel.org>
CC:	<linux-kernel@...r.kernel.org>,
	<linux-f2fs-devel@...ts.sourceforge.net>, <yuchao0@...wei.com>,
	<bintian.wang@...wei.com>
Subject: [RFC] f2fs: fix a race condition between evict & gc

When collecting data segment(gc_data_segment), there is a race condition
between evict and phases of gc:
0) ra_node_page(dnode)
1) ra_node_page(inode)
		<--- evict the inode
2) f2fs_iget get the inode and add it to gc_list 
3) move_data_page

In step 2), f2fs_iget does NOT find the inode and allocs a new inode as result,
which is not resonable.

This patch changes f2fs_iget to ilookup. when no inode is found, no new inode is
created.

Signed-off-by: Hou Pengyang <houpengyang@...wei.com>
---
 fs/f2fs/gc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 38d56f6..6e73193 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -717,8 +717,8 @@ next_step:
 		ofs_in_node = le16_to_cpu(entry->ofs_in_node);
 
 		if (phase == 2) {
-			inode = f2fs_iget(sb, dni.ino);
-			if (IS_ERR(inode) || is_bad_inode(inode))
+			inode = ilookup(sb, dni.ino);
+			if (!inode || IS_ERR(inode) || is_bad_inode(inode))
 				continue;
 
 			/* if encrypted inode, let's go phase 3 */
-- 
1.9.1