Joseph Qi
2013-Dec-16 07:14 UTC
[Ocfs2-devel] [PATCH] ocfs2: fix a tiny race when running dirop_fileop_racer
From: Yiwen Jiang <jiangyiwen at huawei.com>
When running dirop_fileop_racer we found a dead lock case.
2 nodes, say Node A and Node B, mount the same ocfs2 volume. Create
/race/16/1 in the filesystem, and let the inode number of dir 16 is less
than the inode number of dir race.
Node A Node B
mv /race/16/1 /race/
right after Node A has got the
EX mode of /race/16/, and tries to
get EX mode of /race
ls /race/16/
In this case, Node A has got the EX mode of /race/16/, and wants to get
EX mode of /race/. Node B has got the PR mode of /race/, and wants to
get the PR mode of /race/16/. Since EX and PR are mutually exclusive,
dead lock happens.
This patch fixes this case by locking in ancestor order before trying
inode number order.
Signed-off-by: Yiwen Jiang <jiangyiwen at huawei.com>
Signed-off-by: Joseph Qi <joseph.qi at huawei.com>
---
fs/ocfs2/namei.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 95 insertions(+), 2 deletions(-)
diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c
index be3f867..b122684 100644
--- a/fs/ocfs2/namei.c
+++ b/fs/ocfs2/namei.c
@@ -954,6 +954,65 @@ leave:
return status;
}
+static int ocfs2_check_if_ancestor(struct ocfs2_super *osb,
+ u64 src_inode_no, u64 dest_inode_no)
+{
+ int ret = 0, i = 0;
+ u64 parent_inode_no = 0;
+ u64 child_inode_no = src_inode_no;
+ struct inode *child_inode;
+
+#define MAX_LOOKUP_TIMES 32
+ while (1) {
+ child_inode = ocfs2_iget(osb, child_inode_no, 0, 0);
+ if (IS_ERR(child_inode)) {
+ ret = PTR_ERR(child_inode);
+ break;
+ }
+
+ ret = ocfs2_inode_lock(child_inode, NULL, 0);
+ if (ret < 0) {
+ iput(child_inode);
+ if (ret != -ENOENT)
+ mlog_errno(ret);
+ break;
+ }
+
+ ret = ocfs2_lookup_ino_from_name(child_inode, "..", 2,
+ &parent_inode_no);
+ ocfs2_inode_unlock(child_inode, 0);
+ iput(child_inode);
+ if (ret < 0) {
+ ret = -ENOENT;
+ break;
+ }
+
+ if (parent_inode_no == dest_inode_no) {
+ ret = 1;
+ break;
+ }
+
+ if (parent_inode_no == osb->root_inode->i_ino) {
+ ret = 0;
+ break;
+ }
+
+ child_inode_no = parent_inode_no;
+
+ if (++i >= MAX_LOOKUP_TIMES) {
+ mlog(ML_NOTICE, "max lookup times reached, filesystem "
+ "may have nested directories, "
+ "src inode: %llu, dest inode: %llu.\n",
+ (unsigned long long)src_inode_no,
+ (unsigned long long)dest_inode_no);
+ ret = 0;
+ break;
+ }
+ }
+
+ return ret;
+}
+
/*
* The only place this should be used is rename!
* if they have the same id, then the 1st one is the only one locked.
@@ -965,6 +1024,7 @@ static int ocfs2_double_lock(struct ocfs2_super *osb,
struct inode *inode2)
{
int status;
+ int inode1_is_ancestor, inode2_is_ancestor;
struct ocfs2_inode_info *oi1 = OCFS2_I(inode1);
struct ocfs2_inode_info *oi2 = OCFS2_I(inode2);
struct buffer_head **tmpbh;
@@ -978,9 +1038,26 @@ static int ocfs2_double_lock(struct ocfs2_super *osb,
if (*bh2)
*bh2 = NULL;
- /* we always want to lock the one with the lower lockid first. */
+ /* we always want to lock the one with the lower lockid first.
+ * and if they are nested, we lock ancestor first */
if (oi1->ip_blkno != oi2->ip_blkno) {
- if (oi1->ip_blkno < oi2->ip_blkno) {
+ inode1_is_ancestor = ocfs2_check_if_ancestor(osb, oi2->ip_blkno,
+ oi1->ip_blkno);
+ if (inode1_is_ancestor < 0) {
+ status = inode1_is_ancestor;
+ goto bail;
+ }
+
+ inode2_is_ancestor = ocfs2_check_if_ancestor(osb, oi1->ip_blkno,
+ oi2->ip_blkno);
+ if (inode2_is_ancestor < 0) {
+ status = inode2_is_ancestor;
+ goto bail;
+ }
+
+ if ((inode1_is_ancestor == 1) ||
+ (oi1->ip_blkno < oi2->ip_blkno &&
+ inode2_is_ancestor == 0)) {
/* switch id1 and id2 around */
tmpbh = bh2;
bh2 = bh1;
@@ -1097,6 +1174,22 @@ static int ocfs2_rename(struct inode *old_dir,
goto bail;
}
rename_lock = 1;
+
+ /* here we cannot guarantee the inodes haven't just been
+ * changed, so check if they are nested again */
+ status = ocfs2_check_if_ancestor(osb, new_dir->i_ino,
+ old_inode->i_ino);
+ if (status < 0) {
+ mlog_errno(status);
+ goto bail;
+ } else if (status == 1) {
+ status = -EPERM;
+ mlog(ML_ERROR, "src inode %llu should not be ancestor "
+ "of new dir inode %llu\n",
+ (unsigned long long)old_inode->i_ino,
+ (unsigned long long)new_dir->i_ino);
+ goto bail;
+ }
}
/* if old and new are the same, this'll just do one lock. */
--
1.8.4.3