[Ocfs2-devel] [DRAFT 2/2] ocfs2: fix deadlock caused by recursive cluster locking

[Eric Ren]

The deadlock issue happens when running discontiguous block
group testing on multiple nodes. The easier way to reproduce
is to do "chmod -R 777 /mnt/ocfs2" things like this on multiple
nodes at the same time by pssh.

This is indeed another deadlock caused by: commit 743b5f1434f5
("ocfs2: take inode lock in ocfs2_iop_set/get_acl()"). The reason
had been explained well by Tariq Saeed in this thread:

https://oss.oracle.com/pipermail/ocfs2-devel/2015-September/011085.html

For this case, the ocfs2_inode_lock() is misused recursively as below:

do_sys_open
 do_filp_open
  path_openat
   may_open
    inode_permission
     __inode_permission
      ocfs2_permission  <====== ocfs2_inode_lock()
       generic_permission
        get_acl
         ocfs2_iop_get_acl  <====== ocfs2_inode_lock()
          ocfs2_inode_lock_full_nested <===== deadlock if a remote EX request
comes between two ocfs2_inode_lock()

Fix by checking if the cluster lock has been acquired aready in the call-chain
path.

Fixes: commit 743b5f1434f5 ("ocfs2: take inode lock in ocfs2_iop_set/get_acl()")
Signed-off-by: Eric Ren <zren at suse.com>
---
 fs/ocfs2/acl.c | 39 +++++++++++++++++++++++++++------------
 1 file changed, 27 insertions(+), 12 deletions(-)

diff --git a/fs/ocfs2/acl.c b/fs/ocfs2/acl.c
index bed1fcb..7e3544e 100644
--- a/fs/ocfs2/acl.c
+++ b/fs/ocfs2/acl.c
@@ -283,16 +283,24 @@ int ocfs2_set_acl(handle_t *handle,
 int ocfs2_iop_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 {
 	struct buffer_head *bh = NULL;
+	struct ocfs2_holder *oh;
+	struct ocfs2_lock_res *lockres = &OCFS2_I(inode)->ip_inode_lockres;
 	int status = 0;
 
-	status = ocfs2_inode_lock(inode, &bh, 1);
-	if (status < 0) {
-		if (status != -ENOENT)
-			mlog_errno(status);
-		return status;
+	oh = ocfs2_is_locked_by_me(lockres);
+	if (!oh) {
+		status = ocfs2_inode_lock(inode, &bh, 1);
+		if (status < 0) {
+			if (status != -ENOENT)
+				mlog_errno(status);
+			return status;
+		}
 	}
+
 	status = ocfs2_set_acl(NULL, inode, bh, type, acl, NULL, NULL);
-	ocfs2_inode_unlock(inode, 1);
+
+	if (!oh)
+		ocfs2_inode_unlock(inode, 1);
 	brelse(bh);
 	return status;
 }
@@ -302,21 +310,28 @@ struct posix_acl *ocfs2_iop_get_acl(struct inode *inode, int type)
 	struct ocfs2_super *osb;
 	struct buffer_head *di_bh = NULL;
 	struct posix_acl *acl;
+	struct ocfs2_holder *oh;
+	struct ocfs2_lock_res *lockres = &OCFS2_I(inode)->ip_inode_lockres;
 	int ret;
 
 	osb = OCFS2_SB(inode->i_sb);
 	if (!(osb->s_mount_opt & OCFS2_MOUNT_POSIX_ACL))
 		return NULL;
-	ret = ocfs2_inode_lock(inode, &di_bh, 0);
-	if (ret < 0) {
-		if (ret != -ENOENT)
-			mlog_errno(ret);
-		return ERR_PTR(ret);
+
+	oh = ocfs2_is_locked_by_me(lockres);
+	if (!oh) {
+		ret = ocfs2_inode_lock(inode, &di_bh, 0);
+		if (ret < 0) {
+			if (ret != -ENOENT)
+				mlog_errno(ret);
+			return ERR_PTR(ret);
+		}
 	}
 
 	acl = ocfs2_get_acl_nolock(inode, type, di_bh);
 
-	ocfs2_inode_unlock(inode, 0);
+	if (!oh)
+		ocfs2_inode_unlock(inode, 0);
 	brelse(di_bh);
 	return acl;
 }
-- 
2.6.6