Ocfs2 devel - May 2016 - [patch 1/6] ocfs2: o2hb: add negotiate timer

From: Junxiao Bi <junxiao.bi at oracle.com>
Subject: ocfs2: o2hb: add negotiate timer

This series of patches is to fix the issue that when storage down, all
nodes will fence self due to write timeout.

With this patch set, all nodes will keep going until storage back online,
except if the following issue happens, then all nodes will do as before to
fence self.

1. io error got
2. network between nodes down
3. nodes panic

This patch (of 6):

When storage down, all nodes will fence self due to write timeout.  The
negotiate timer is designed to avoid this, with it node will wait until
storage up again.

Negotiate timer working in the following way:

1. The timer expires before write timeout timer, its timeout is half
   of write timeout now.  It is re-queued along with write timeout timer.
   If expires, it will send NEGO_TIMEOUT message to master node(node with
   lowest node number).  This message does nothing but marks a bit in a
   bitmap recording which nodes are negotiating timeout on master node.

2. If storage down, nodes will send this message to master node, then
   when master node finds its bitmap including all online nodes, it sends
   NEGO_APPROVL message to all nodes one by one, this message will
   re-queue write timeout timer and negotiate timer.  For any node doesn't
   receive this message or meets some issue when handling this message, it
   will be fenced.  If storage up at any time, o2hb_thread will run and
   re-queue all the timer, nothing will be affected by these two steps.

Signed-off-by: Junxiao Bi <junxiao.bi at oracle.com>
Reviewed-by: Ryan Ding <ryan.ding at oracle.com>
Cc: Gang He <ghe at suse.com>
Cc: rwxybh <rwxybh at 126.com>
Cc: Mark Fasheh <mfasheh at suse.de>
Cc: Joel Becker <jlbec at evilplan.org>
Cc: Joseph Qi <joseph.qi at huawei.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
---

 fs/ocfs2/cluster/heartbeat.c |   51 ++++++++++++++++++++++++++++++---
 1 file changed, 47 insertions(+), 4 deletions(-)

diff -puN fs/ocfs2/cluster/heartbeat.c~ocfs2-o2hb-add-negotiate-timer
fs/ocfs2/cluster/heartbeat.c
--- a/fs/ocfs2/cluster/heartbeat.c~ocfs2-o2hb-add-negotiate-timer
+++ a/fs/ocfs2/cluster/heartbeat.c
@@ -272,6 +272,10 @@ struct o2hb_region {
 	struct delayed_work	hr_write_timeout_work;
 	unsigned long		hr_last_timeout_start;
 
+	/* negotiate timer, used to negotiate extending hb timeout. */
+	struct delayed_work	hr_nego_timeout_work;
+	unsigned long		hr_nego_node_bitmap[BITS_TO_LONGS(O2NM_MAX_NODES)];
+
 	/* Used during o2hb_check_slot to hold a copy of the block
 	 * being checked because we temporarily have to zero out the
 	 * crc field. */
@@ -319,7 +323,7 @@ static void o2hb_write_timeout(struct wo
 	o2quo_disk_timeout();
 }
 
-static void o2hb_arm_write_timeout(struct o2hb_region *reg)
+static void o2hb_arm_timeout(struct o2hb_region *reg)
 {
 	/* Arm writeout only after thread reaches steady state */
 	if (atomic_read(&reg->hr_steady_iterations) != 0)
@@ -337,11 +341,49 @@ static void o2hb_arm_write_timeout(struc
 	reg->hr_last_timeout_start = jiffies;
 	schedule_delayed_work(&reg->hr_write_timeout_work,
 			      msecs_to_jiffies(O2HB_MAX_WRITE_TIMEOUT_MS));
+
+	cancel_delayed_work(&reg->hr_nego_timeout_work);
+	/* negotiate timeout must be less than write timeout. */
+	schedule_delayed_work(&reg->hr_nego_timeout_work,
+			      msecs_to_jiffies(O2HB_MAX_WRITE_TIMEOUT_MS)/2);
+	memset(reg->hr_nego_node_bitmap, 0, sizeof(reg->hr_nego_node_bitmap));
 }
 
-static void o2hb_disarm_write_timeout(struct o2hb_region *reg)
+static void o2hb_disarm_timeout(struct o2hb_region *reg)
 {
 	cancel_delayed_work_sync(&reg->hr_write_timeout_work);
+	cancel_delayed_work_sync(&reg->hr_nego_timeout_work);
+}
+
+static void o2hb_nego_timeout(struct work_struct *work)
+{
+	unsigned long live_node_bitmap[BITS_TO_LONGS(O2NM_MAX_NODES)];
+	int master_node;
+	struct o2hb_region *reg;
+
+	reg = container_of(work, struct o2hb_region, hr_nego_timeout_work.work);
+	o2hb_fill_node_map(live_node_bitmap, sizeof(live_node_bitmap));
+	/* lowest node as master node to make negotiate decision. */
+	master_node = find_next_bit(live_node_bitmap, O2NM_MAX_NODES, 0);
+
+	if (master_node == o2nm_this_node()) {
+		set_bit(master_node, reg->hr_nego_node_bitmap);
+		if (memcmp(reg->hr_nego_node_bitmap, live_node_bitmap,
+				sizeof(reg->hr_nego_node_bitmap))) {
+			/* check negotiate bitmap every second to do timeout
+			 * approve decision.
+			 */
+			schedule_delayed_work(&reg->hr_nego_timeout_work,
+				msecs_to_jiffies(1000));
+
+			return;
+		}
+
+		/* approve negotiate timeout request. */
+	} else {
+		/* negotiate timeout with master node. */
+	}
+
 }
 
 static inline void o2hb_bio_wait_init(struct o2hb_bio_wait_ctxt *wc)
@@ -1032,7 +1074,7 @@ static int o2hb_do_disk_heartbeat(struct
 	/* Skip disarming the timeout if own slot has stale/bad data */
 	if (own_slot_ok) {
 		o2hb_set_quorum_device(reg);
-		o2hb_arm_write_timeout(reg);
+		o2hb_arm_timeout(reg);
 	}
 
 bail:
@@ -1114,7 +1156,7 @@ static int o2hb_thread(void *data)
 		}
 	}
 
-	o2hb_disarm_write_timeout(reg);
+	o2hb_disarm_timeout(reg);
 
 	/* unclean stop is only used in very bad situation */
 	for(i = 0; !reg->hr_unclean_stop && i < reg->hr_blocks; i++)
@@ -1762,6 +1804,7 @@ static ssize_t o2hb_region_dev_store(str
 	}
 
 	INIT_DELAYED_WORK(&reg->hr_write_timeout_work, o2hb_write_timeout);
+	INIT_DELAYED_WORK(&reg->hr_nego_timeout_work, o2hb_nego_timeout);
 
 	/*
 	 * A node is considered live after it has beat LIVE_THRESHOLD
_

On Mon, May 23, 2016 at 02:50:28PM -0700, Andrew Morton
wrote:
> From: Junxiao Bi <junxiao.bi at oracle.com>
> Subject: ocfs2: o2hb: add negotiate timer
Thank you for the well written patch description by the way.

> This series of patches is to fix the issue that when storage down, all
> nodes will fence self due to write timeout.
> 
> With this patch set, all nodes will keep going until storage back online,
> except if the following issue happens, then all nodes will do as before to
> fence self.
> 
> 1. io error got
> 2. network between nodes down
> 3. nodes panic
> 
> This patch (of 6):
> 
> When storage down, all nodes will fence self due to write timeout.  The
> negotiate timer is designed to avoid this, with it node will wait until
> storage up again.
> 
> Negotiate timer working in the following way:
> 
> 1. The timer expires before write timeout timer, its timeout is half
>    of write timeout now.  It is re-queued along with write timeout timer.
>    If expires, it will send NEGO_TIMEOUT message to master node(node with
>    lowest node number).  This message does nothing but marks a bit in a
>    bitmap recording which nodes are negotiating timeout on master node.
I went through the patch series, and generally feel that the code
is well written and straight forward. I have two issues regarding
how this operates. Otherwise, I like the general direction this
is taking.

The first is easy - we're updating the o2cb network protocol and
need to bump the protocol version otherwise a node that doesn't
speak these new messages could mount and even be selected as the
'master' without actually being able to participate in this scheme.


My other concern is whether the notion of 'lowest node' can
change if one comes online while the cluster is negotiating this
timeout. Obviously in the case where all the disks are unplugged
this couldn't happen because a new node couldn't begin to
heartbeat.

What about a situation where only some nodes are negotiating this
timeout? On the ones which have no disk access, lowest node
number still won't change since they can't read the new
heartbeats. On those with stable access though, can't this value
change? How does that effect this algorithm?

Thanks,
	--Mark

--
Mark Fasheh