ocfs2: Move orphan scan work to ocfs2_wq.

We used to let orphan scan work in the default work queue, but there is a corner case which will make the system deadlock. The scenario is like this:
1. set heartbeat threadshold to 200. this will allow us to have a great chance to have a orphan scan work before our quorum decision.
2. mount node 1.
3. after 1~2 minutes, mount node 2(in order to make the bug easier to reproduce, better add maxcpus=1 to kernel command line).
4. node 1 do orphan scan work.
5. node 2 do orphan scan work.
6. node 1 do orphan scan work. After this, node 1 hold the orphan scan lock while node 2 know node 1 is the master.
7. ifdown eth2 in node 2(eth2 is what we do ocfs2 interconnection).

Now when node 2 begins orphan scan, the system queue is blocked.

The root cause is that both orphan scan work and quorum decision work will use the system event work queue. orphan scan has a chance of blocking the event work queue(in dlm_wait_for_node_death) so that there is no chance for quorum decision work to proceed.

This patch resolve it by moving orphan scan work to ocfs2_wq.

Signed-off-by Tao Ma <[email protected]>

---
 fs/ocfs2/journal.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

fs/ocfs2/journal.c +3 -3

index 57e3fef..e02788f 100644
@@ -1938,7 +1938,7 @@ void ocfs2_orphan_scan_work(struct work_struct *work)
 	mutex_lock(&os->os_lock);
 	ocfs2_queue_orphan_scan(osb);
 	if (atomic_read(&os->os_state) == ORPHAN_SCAN_ACTIVE)
-		schedule_delayed_work(&os->os_orphan_scan_work,
+		queue_delayed_work(ocfs2_wq, &os->os_orphan_scan_work,
 				      ocfs2_orphan_scan_timeout());
 	mutex_unlock(&os->os_lock);
 }

@@ -1978,8 +1978,8 @@ void ocfs2_orphan_scan_start(struct ocfs2_super *osb)
 		atomic_set(&os->os_state, ORPHAN_SCAN_INACTIVE);
 	else {
 		atomic_set(&os->os_state, ORPHAN_SCAN_ACTIVE);
-		schedule_delayed_work(&os->os_orphan_scan_work,
-				      ocfs2_orphan_scan_timeout());
+		queue_delayed_work(ocfs2_wq, &os->os_orphan_scan_work,
+				   ocfs2_orphan_scan_timeout());
 	}
 }
 

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Hi Tao,

Checking the workers in ocfs2_wq, I found osb_truncate_log_wq. The worker function ocfs2_truncate_log_worker() can with the following call trace.

ocfs2_truncate_log_worker()
ocfs2_flush_truncate_log()
__ocfs2_flush_truncate_log()
ocfs2_inode_lock()

So I think during ocfs2_inode_lock(), we still have the possibility that it hang the work queue at dlm_wait_for_node_death().

So maybe a dedicated work queue is the only choice?

regards,
wengang.

Quoted 60 lines · Tao Ma

We used to let orphan scan work in the default work queue, but there is a corner case which will make the system deadlock. The scenario is like this:
1. set heartbeat threadshold to 200. this will allow us to have a great chance to have a orphan scan work before our quorum decision.
2. mount node 1.
3. after 1~2 minutes, mount node 2(in order to make the bug easier to reproduce, better add maxcpus=1 to kernel command line).
4. node 1 do orphan scan work.
5. node 2 do orphan scan work.
6. node 1 do orphan scan work. After this, node 1 hold the orphan scan lock while node 2 know node 1 is the master.
7. ifdown eth2 in node 2(eth2 is what we do ocfs2 interconnection).

Now when node 2 begins orphan scan, the system queue is blocked.

The root cause is that both orphan scan work and quorum decision work will use the system event work queue. orphan scan has a chance of blocking the event work queue(in dlm_wait_for_node_death) so that there is no chance for quorum decision work to proceed.

This patch resolve it by moving orphan scan work to ocfs2_wq.

Signed-off-by Tao Ma <[email protected]>

---
 fs/ocfs2/journal.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

fs/ocfs2/journal.c +3 -3

index 57e3fef..e02788f 100644
@@ -1938,7 +1938,7 @@ void ocfs2_orphan_scan_work(struct work_struct *work)
 	mutex_lock(&os->os_lock);
 	ocfs2_queue_orphan_scan(osb);
 	if (atomic_read(&os->os_state) == ORPHAN_SCAN_ACTIVE)
-		schedule_delayed_work(&os->os_orphan_scan_work,
+		queue_delayed_work(ocfs2_wq, &os->os_orphan_scan_work,
 				      ocfs2_orphan_scan_timeout());
 	mutex_unlock(&os->os_lock);
 }

@@ -1978,8 +1978,8 @@ void ocfs2_orphan_scan_start(struct ocfs2_super *osb)
 		atomic_set(&os->os_state, ORPHAN_SCAN_INACTIVE);
 	else {
 		atomic_set(&os->os_state, ORPHAN_SCAN_ACTIVE);
-		schedule_delayed_work(&os->os_orphan_scan_work,
-				      ocfs2_orphan_scan_timeout());
+		queue_delayed_work(ocfs2_wq, &os->os_orphan_scan_work,
+				   ocfs2_orphan_scan_timeout());
 	}
 }
 

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_______________________________________________
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Ocfs2-devel at oss.oracle.com
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_______________________________________________
Ocfs2-devel mailing list
Ocfs2-devel at oss.oracle.com
http://oss.oracle.com/mailman/listinfo/ocfs2-devel

We used to let orphan scan work in the default work queue, but there is a corner case which will make the system deadlock. The scenario is like this:
1. set heartbeat threadshold to 200. this will allow us to have a great chance to have a orphan scan work before our quorum decision.
2. mount node 1.
3. after 1~2 minutes, mount node 2(in order to make the bug easier to reproduce, better add maxcpus=1 to kernel command line).
4. node 1 do orphan scan work.
5. node 2 do orphan scan work.
6. node 1 do orphan scan work. After this, node 1 hold the orphan scan lock while node 2 know node 1 is the master.
7. ifdown eth2 in node 2(eth2 is what we do ocfs2 interconnection).

Now when node 2 begins orphan scan, the system queue is blocked.

The root cause is that both orphan scan work and quorum decision work will use the system event work queue. orphan scan has a chance of blocking the event work queue(in dlm_wait_for_node_death) so that there is no chance for quorum decision work to proceed.

This patch resolve it by moving orphan scan work to ocfs2_wq.

Signed-off-by Tao Ma<[email protected]>

---
  fs/ocfs2/journal.c |    6 +++---
  1 files changed, 3 insertions(+), 3 deletions(-)

fs/ocfs2/journal.c +3 -3

index 57e3fef..e02788f 100644
@@ -1938,7 +1938,7 @@ void ocfs2_orphan_scan_work(struct work_struct *work)
  	mutex_lock(&os->os_lock);
  	ocfs2_queue_orphan_scan(osb);
  	if (atomic_read(&os->os_state) == ORPHAN_SCAN_ACTIVE)
-		schedule_delayed_work(&os->os_orphan_scan_work,
+		queue_delayed_work(ocfs2_wq,&os->os_orphan_scan_work,
  				      ocfs2_orphan_scan_timeout());
  	mutex_unlock(&os->os_lock);
  }

@@ -1978,8 +1978,8 @@ void ocfs2_orphan_scan_start(struct ocfs2_super *osb)
  		atomic_set(&os->os_state, ORPHAN_SCAN_INACTIVE);
  	else {
  		atomic_set(&os->os_state, ORPHAN_SCAN_ACTIVE);
-		schedule_delayed_work(&os->os_orphan_scan_work,
-				      ocfs2_orphan_scan_timeout());
+		queue_delayed_work(ocfs2_wq,&os->os_orphan_scan_work,
+				   ocfs2_orphan_scan_timeout());
  	}
  }
 

We used to let orphan scan work in the default work queue, but there is a corner case which will make the system deadlock. The scenario is like this:
1. set heartbeat threadshold to 200. this will allow us to have a great chance to have a orphan scan work before our quorum decision.
2. mount node 1.
3. after 1~2 minutes, mount node 2(in order to make the bug easier to reproduce, better add maxcpus=1 to kernel command line).
4. node 1 do orphan scan work.
5. node 2 do orphan scan work.
6. node 1 do orphan scan work. After this, node 1 hold the orphan scan lock while node 2 know node 1 is the master.
7. ifdown eth2 in node 2(eth2 is what we do ocfs2 interconnection).

Now when node 2 begins orphan scan, the system queue is blocked.

The root cause is that both orphan scan work and quorum decision work will use the system event work queue. orphan scan has a chance of blocking the event work queue(in dlm_wait_for_node_death) so that there is no chance for quorum decision work to proceed.

This patch resolve it by moving orphan scan work to ocfs2_wq.

Signed-off-by Tao Ma <[email protected]>