3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Pan Bian <bianpan2...@163.com>

commit 0ea295dd853e0879a9a30ab61f923c26be35b902 upstream.

The function truncate_node frees the page with f2fs_put_page. However,
the page index is read after that. So, the patch reads the index before
freeing the page.

Fixes: bf39c00a9a7f ("f2fs: drop obsolete node page when it is truncated")
Cc: <sta...@vger.kernel.org>
Signed-off-by: Pan Bian <bianpan2...@163.com>
Reviewed-by: Chao Yu <yuch...@huawei.com>
Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org>
Signed-off-by: Sudip Mukherjee <sudipm.mukher...@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 fs/f2fs/node.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -565,6 +565,7 @@ static void truncate_node(struct dnode_o
 {
        struct f2fs_sb_info *sbi = F2FS_I_SB(dn->inode);
        struct node_info ni;
+       pgoff_t index;
 
        get_node_info(sbi, dn->nid, &ni);
        if (dn->inode->i_blocks == 0) {
@@ -588,10 +589,11 @@ invalidate:
        clear_node_page_dirty(dn->node_page);
        F2FS_SET_SB_DIRT(sbi);
 
+       index = dn->node_page->index;
        f2fs_put_page(dn->node_page, 1);
 
        invalidate_mapping_pages(NODE_MAPPING(sbi),
-                       dn->node_page->index, dn->node_page->index);
+                       index, index);
 
        dn->node_page = NULL;
        trace_f2fs_truncate_node(dn->inode, dn->nid, ni.blk_addr);


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