nilfs2: missing a read lock for segment writer in nilfs_attach_checkpoint()

'ns_cno' of structure 'the_nilfs' must be protected from segment
writer, in other words, the caller of nilfs_get_checkpoint should hold
read lock for nilfs->ns_segctor_sem.  This patch adds the lock/unlock
operations in nilfs_attach_checkpoint() when calling
nilfs_cpfile_get_checkpoint().

Signed-off-by: Zhang Qiang <zhangqiang.buaa@gmail.com>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index 8e2ec43b18f4..151964f0de4c 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -416,8 +416,10 @@ int nilfs_attach_checkpoint(struct nilfs_sb_info *sbi, __u64 cno)
         if (unlikely(err))
                 goto failed;
 
+        down_read(&nilfs->ns_segctor_sem);
         err = nilfs_cpfile_get_checkpoint(nilfs->ns_cpfile, cno, 0, &raw_cp,
                                           &bh_cp);
+        up_read(&nilfs->ns_segctor_sem);
         if (unlikely(err)) {
                 if (err == -ENOENT || err == -EINVAL) {
                         printk(KERN_ERR