[3.8.y.z extended stable] Patch "ocfs2: dlm: fix recovery hung" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ocfs2: dlm: fix recovery hung

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.22.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 8648abd257708c5f5df7a7d7483238f71fe2c8d2 Mon Sep 17 00:00:00 2001
From: Junxiao Bi <junxiao.bi at oracle.com>
Date: Thu, 3 Apr 2014 14:46:51 -0700
Subject: ocfs2: dlm: fix recovery hung

commit ded2cf71419b9353060e633b59e446c42a6a2a09 upstream.

There is a race window in dlm_do_recovery() between dlm_remaster_locks()
and dlm_reset_recovery() when the recovery master nearly finish the
recovery process for a dead node.  After the master sends FINALIZE_RECO
message in dlm_remaster_locks(), another node may become the recovery
master for another dead node, and then send the BEGIN_RECO message to
all the nodes included the old master, in the handler of this message
dlm_begin_reco_handler() of old master, dlm->reco.dead_node and
dlm->reco.new_master will be set to the second dead node and the new
master, then in dlm_reset_recovery(), these two variables will be reset
to default value.  This will cause new recovery master can not finish
the recovery process and hung, at last the whole cluster will hung for
recovery.

old recovery master:                                 new recovery master:
dlm_remaster_locks()
                                                  become recovery master for
                                                  another dead node.
                                                  dlm_send_begin_reco_message()
dlm_begin_reco_handler()
{
 if (dlm->reco.state & DLM_RECO_STATE_FINALIZE) {
  return -EAGAIN;
 }
 dlm_set_reco_master(dlm, br->node_idx);
 dlm_set_reco_dead_node(dlm, br->dead_node);
}
dlm_reset_recovery()
{
 dlm_set_reco_dead_node(dlm, O2NM_INVALID_NODE_NUM);
 dlm_set_reco_master(dlm, O2NM_INVALID_NODE_NUM);
}
                                                  will hang in dlm_remaster_locks() for
                                                  request dlm locks info

Before send FINALIZE_RECO message, recovery master should set
DLM_RECO_STATE_FINALIZE for itself and clear it after the recovery done,
this can break the race windows as the BEGIN_RECO messages will not be
handled before DLM_RECO_STATE_FINALIZE flag is cleared.

A similar race may happen between new recovery master and normal node
which is in dlm_finalize_reco_handler(), also fix it.

Signed-off-by: Junxiao Bi <junxiao.bi at oracle.com>
Reviewed-by: Srinivas Eeda <srinivas.eeda at oracle.com>
Reviewed-by: Wengang Wang <wen.gang.wang at oracle.com>
Cc: Joel Becker <jlbec at evilplan.org>
Cc: Mark Fasheh <mfasheh at suse.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/ocfs2/dlm/dlmrecovery.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
index df3cfd3..d15b071 100644
--- a/fs/ocfs2/dlm/dlmrecovery.c
+++ b/fs/ocfs2/dlm/dlmrecovery.c
@@ -540,7 +540,10 @@ master_here:
 		/* success!  see if any other nodes need recovery */
 		mlog(0, "DONE mastering recovery of %s:%u here(this=%u)!\n",
 		     dlm->name, dlm->reco.dead_node, dlm->node_num);
-		dlm_reset_recovery(dlm);
+		spin_lock(&dlm->spinlock);
+		__dlm_reset_recovery(dlm);
+		dlm->reco.state &= ~DLM_RECO_STATE_FINALIZE;
+		spin_unlock(&dlm->spinlock);
 	}
 	dlm_end_recovery(dlm);

@@ -698,6 +701,14 @@ static int dlm_remaster_locks(struct dlm_ctxt *dlm, u8 dead_node)
 		if (all_nodes_done) {
 			int ret;

+			/* Set this flag on recovery master to avoid
+			 * a new recovery for another dead node start
+			 * before the recovery is not done. That may
+			 * cause recovery hung.*/
+			spin_lock(&dlm->spinlock);
+			dlm->reco.state |= DLM_RECO_STATE_FINALIZE;
+			spin_unlock(&dlm->spinlock);
+
 			/* all nodes are now in DLM_RECO_NODE_DATA_DONE state
 	 		 * just send a finalize message to everyone and
 	 		 * clean up */
@@ -2872,8 +2883,8 @@ int dlm_finalize_reco_handler(struct o2net_msg *msg, u32 len, void *data,
 				BUG();
 			}
 			dlm->reco.state &= ~DLM_RECO_STATE_FINALIZE;
+			__dlm_reset_recovery(dlm);
 			spin_unlock(&dlm->spinlock);
-			dlm_reset_recovery(dlm);
 			dlm_kick_recovery_thread(dlm);
 			break;
 		default:
--
1.9.1