[ClusterLabs] corosync race condition when node leaves immediately after joining

Jonathan Davies jonathan.davies at citrix.com
Mon Oct 16 09:05:43 EDT 2017



On 13/10/17 17:24, Jan Friesse wrote:
>> I've done a bit of digging and am getting closer to the root cause of
>> the race.
>>
>> We rely on having votequorum_sync_init called twice -- once when node 1
>> joins (with member_list_entries=2) and once when node 1 leaves (with
>> member_list_entries=1). This is important because votequorum_sync_init
>> marks nodes as NODESTATE_DEAD if they are not in quorum_members[] -- so
>> it needs to have seen the node appear then disappear. This is important
>> because get_total_votes only counts votes from nodes in state
>> NODESTATE_MEMBER.
> 
> So there are basically two problems.
> 
> Actually first (main) problem is that votequorum_sync_init is ever 
> called when that node joins. It really shouldn't. And problem is simply 
> because calling api->shutdown_request() is not enough. Can you try 
> replace it with exit(1) (for testing) and reproduce the problem? I'm 
> pretty sure problem disappears.

No, the problem still happens :-(

I am using the following patch:

diff --git a/exec/cmap.c b/exec/cmap.c
index de730d2..1125cef 100644
--- a/exec/cmap.c
+++ b/exec/cmap.c
@@ -406,7 +406,7 @@ static void cmap_sync_activate (void)
                 log_printf(LOGSYS_LEVEL_ERROR,
                     "Received config version (%"PRIu64") is different 
than my config version (%"PRIu64")! Exiting",
                     cmap_highest_config_version_received, 
cmap_my_config_version);
-               api->shutdown_request();
+               exit(1);
                 return ;
         }
  }
diff --git a/exec/main.c b/exec/main.c
index b0d5639..4fd3e68 100644
--- a/exec/main.c
+++ b/exec/main.c
@@ -627,6 +627,7 @@ static void deliver_fn (
                         ((void *)msg);
         }

+       log_printf(LOGSYS_LEVEL_NOTICE, "executing '%s' exec_handler_fn 
%p for node %d (fn %d)", corosync_service[service]->name, 
corosync_service[service]->exec_engine[fn_id].exec_handler_fn, nodeid, 
fn_id);
         corosync_service[service]->exec_engine[fn_id].exec_handler_fn
                 (msg, nodeid);
  }
diff --git a/exec/votequorum.c b/exec/votequorum.c
index 1a97c6d..7c0f34f 100644
--- a/exec/votequorum.c
+++ b/exec/votequorum.c
@@ -2099,6 +2100,7 @@ static void 
message_handler_req_exec_votequorum_nodeinfo (
         node->flags = req_exec_quorum_nodeinfo->flags;
         node->votes = req_exec_quorum_nodeinfo->votes;
         node->state = NODESTATE_MEMBER;
+       log_printf(LOGSYS_LEVEL_NOTICE, 
"message_handler_req_exec_votequorum_nodeinfo (%p) marking node %d as 
MEMBER", message_handler_req_exec_votequorum_nodeinfo, nodeid);

         if (node->flags & NODE_FLAGS_LEAVING) {
                 node->state = NODESTATE_LEAVING;

When it's working correctly I see this:

1508151960.072927 notice  [TOTEM ] A new membership (10.71.218.17:2304) 
was formed. Members joined: 1
1508151960.073082 notice  [SYNC  ] calling sync_init on service 
'corosync configuration map access' (0) with my_member_list_entries = 2
1508151960.073150 notice  [MAIN  ] executing 'corosync configuration map 
access' exec_handler_fn 0x55b5eb504ca0 for node 1 (fn 0)
1508151960.073197 notice  [MAIN  ] executing 'corosync configuration map 
access' exec_handler_fn 0x55b5eb504ca0 for node 2 (fn 0)
1508151960.073238 notice  [SYNC  ] calling sync_init on service 
'corosync cluster closed process group service v1.01' (1) with 
my_member_list_entries = 2
1508151961.073033 notice  [TOTEM ] A processor failed, forming new 
configuration.

When it's not working correctly I see this:

1508151908.447584 notice  [TOTEM ] A new membership (10.71.218.17:2292) 
was formed. Members joined: 1
1508151908.447757 notice  [MAIN  ] executing 'corosync vote quorum 
service v1.0' exec_handler_fn 0x558b39fbbaa0 for node 1 (fn 0)
1508151908.447866 notice  [VOTEQ ] 
message_handler_req_exec_votequorum_nodeinfo (0x558b39fbbaa0) marking 
node 1 as MEMBER
1508151908.447972 notice  [VOTEQ ] get_total_votes: node 1 is a MEMBER 
so counting vote
1508151908.448045 notice  [VOTEQ ] get_total_votes: node 2 is a MEMBER 
so counting vote
1508151908.448091 notice  [QUORUM] This node is within the primary 
component and will provide service.
1508151908.448134 notice  [QUORUM] Members[1]: 2
1508151908.448175 notice  [SYNC  ] calling sync_init on service 
'corosync configuration map access' (0) with my_member_list_entries = 2
1508151908.448205 notice  [MAIN  ] executing 'corosync configuration map 
access' exec_handler_fn 0x558b39fb3ca0 for node 1 (fn 0)
1508151908.448247 notice  [MAIN  ] executing 'corosync configuration map 
access' exec_handler_fn 0x558b39fb3ca0 for node 2 (fn 0)
1508151908.448307 notice  [SYNC  ] calling sync_init on service 
'corosync cluster closed process group service v1.01' (1) with 
my_member_list_entries = 2
1508151909.447182 notice  [TOTEM ] A processor failed, forming new 
configuration.

... and at that point I already see "Total votes: 2" in the 
corosync-quorumtool output.

The key difference seems to be whether votequorum's nodeinfo 
exec_handler_fn is called. If it is called, it marks the node as 
NODESTATE_MEMBER, which is sufficient to trigger the bug because it is 
never subsequently marked as NODESTATE_DEAD.

(Note that in both cases there is now a one-second delay before the "A 
processor failed" message. This is due to calling exit(1) rather than 
api->shutdown_request().)

>> When it goes wrong, I see that votequorum_sync_init is only called
>> *once* (with member_list_entries=1) -- after node 1 has joined and left.
>> So it never sees node 1 in member_list, hence never marks it as
>> NODESTATE_DEAD. But message_handler_req_exec_votequorum_nodeinfo has
>> indepedently marked the node as NODESTATE_MEMBER, hence get_total_votes
>> counts it and quorate is set to 1.
> 
> This is second problem and it has to be also fixed. You have to be 
> pretty lucky to reproduce it so often.
> 
> Anyway, here is theory:
> - node 1 calls api->shutdown_request() and continue processing (this is 
> problem 1)
> - both nodes gets to a state where they should call 
> votequorum_sync_init, but node 2 is now not scheduled (as I said, it 
> must be pretty luck)
> - node 1 calls votequorum_sync_init and votequorum_sync_process (sending 
> nodeinfo) and it's shutdown
> - node 2 gets nodeinfo
> - node 2 sees node 1 shutdown
> - node 2 calls votequorum_sync_init and votequorum_sync_process
> 
> If this theory is true, we must probably fix the sync.c to have 2 or 
> ideally 3-4 barriers instead of 1.
> 
>>
>> So why is votequorum_sync_init sometimes only called once? It looks like
>> it's all down to whether we manage to iterate through all the calls to
>> schedwrk_processor before entering the OPERATIONAL state. I haven't yet
>> looked into exactly what controls the timing of these two things.
>>
>> Adding the following patch helps me to demonstrate the problem more
>> clearly:
>>
>> diff --git a/exec/sync.c b/exec/sync.c
>> index e7b71bd..a2fb06d 100644
>> --- a/exec/sync.c
>> +++ b/exec/sync.c
>> @@ -544,6 +545,7 @@ static int schedwrk_processor (const void *context)
>>                  }
>>
>>                  if
>> (my_sync_callbacks_retrieve(my_service_list[my_processing_idx].service_id, 
>>
>> NULL) != -1) {
>> +                       log_printf(LOGSYS_LEVEL_NOTICE, "calling
>> sync_init on service '%s' (%d) with my_member_list_entries = %d",
>> my_service_list[my_processing_idx].name, my_processing_idx,
>> my_member_list_entries);
>>                          my_service_list[my_processing_idx].sync_init
>> (my_trans_list,
>>                                  my_trans_list_entries, my_member_list,
>>                                  my_member_list_entries,
>> diff --git a/exec/votequorum.c b/exec/votequorum.c
>> index d5f06c1..aab6c15 100644
>> --- a/exec/votequorum.c
>> +++ b/exec/votequorum.c
>> @@ -2336,6 +2353,8 @@ static void votequorum_sync_init (
>>          int left_nodes;
>>          struct cluster_node *node;
>>
>> +       log_printf(LOGSYS_LEVEL_NOTICE, "votequorum_sync_init has %d
>> member_list_entries", member_list_entries);
>> +
>>          ENTER();
>>
>>          sync_in_progress = 1;
>>
>> When it works correctly I see the following (selected log lines):
>>
>> notice  [TOTEM ] A new membership (10.71.218.17:2016) was formed.
>> Members joined: 1
>> notice  [SYNC  ] calling sync_init on service 'corosync configuration
>> map access' (0) with my_member_list_entries = 2
>> notice  [SYNC  ] calling sync_init on service 'corosync cluster closed
>> process group service v1.01' (1) with my_member_list_entries = 2
>> notice  [SYNC  ] calling sync_init on service 'corosync vote quorum
>> service v1.0' (2) with my_member_list_entries = 2
>> notice  [VOTEQ ] votequorum_sync_init has 2 member_list_entries
>> notice  [TOTEM ] A new membership (10.71.218.18:2020) was formed.
>> Members left: 1
>> notice  [SYNC  ] calling sync_init on service 'corosync configuration
>> map access' (0) with my_member_list_entries = 1
>> notice  [SYNC  ] calling sync_init on service 'corosync cluster closed
>> process group service v1.01' (1) with my_member_list_entries = 1
>> notice  [SYNC  ] calling sync_init on service 'corosync vote quorum
>> service v1.0' (2) with my_member_list_entries = 1
>> notice  [VOTEQ ] votequorum_sync_init has 1 member_list_entries
>>
>>   -- Notice that votequorum_sync_init is called once with 2 members and
>> once with 1 member.
>>
>> When it goes wrong I see the following (selected log lines):
>>
>> notice  [TOTEM ] A new membership (10.71.218.17:2004) was formed.
>> Members joined: 1
>> notice  [SYNC  ] calling sync_init on service 'corosync configuration
>> map access' (0) with my_member_list_entries = 2
>> notice  [SYNC  ] calling sync_init on service 'corosync cluster closed
>> process group service v1.01' (1) with my_member_list_entries = 2
>> notice  [TOTEM ] A new membership (10.71.218.18:2008) was formed.
>> Members left: 1
>> notice  [SYNC  ] calling sync_init on service 'corosync configuration
>> map access' (0) with my_member_list_entries = 1
>> notice  [SYNC  ] calling sync_init on service 'corosync cluster closed
>> process group service v1.01' (1) with my_member_list_entries = 1
>> notice  [SYNC  ] calling sync_init on service 'corosync vote quorum
>> service v1.0' (2) with my_member_list_entries = 1
>> notice  [VOTEQ ] votequorum_sync_init has 1 member_list_entries
>>
>>   -- Notice the value of my_member_list_entries in the different
>> sync_init calls, and that votequorum_sync_init is only called once.
>>
>> Does this help explain the issue?
> 
> It's definitively helpful. I will try to thing about what may be 
> happening a little deeper. Can you please add similar debug info as you 
> have for sync_init also to other sync_ and send me the log of both nodes 
> when everything works and when do not?

Okay. I've rolled back to make the call to api->shutdown_request() on 
config_version mismatch, and have added debug lines in sync.c just 
before calls to sync_activate, sync_abort and sync_process.

When it's working correctly:

1508158482.991782 notice  [TOTEM ] A new membership (10.71.218.17:2384) 
was formed. Members joined: 1
1508158482.991930 notice  [MAIN  ] executing 'corosync vote quorum 
service v1.0' exec_handler_fn 0x56492b0d6bf0 for node 1 (fn 0)
1508158482.992029 notice  [VOTEQ ] 
message_handler_req_exec_votequorum_nodeinfo (0x56492b0d6bf0) marking 
node 1 as MEMBER
1508158482.992122 notice  [VOTEQ ] get_total_votes: node 1 is a MEMBER 
so counting vote
1508158482.992206 notice  [VOTEQ ] get_total_votes: node 2 is a MEMBER 
so counting vote
1508158482.992263 notice  [QUORUM] This node is within the primary 
component and will provide service.
1508158482.992307 notice  [QUORUM] Members[1]: 2
1508158482.992351 notice  [SYNC  ] calling sync_init on service 
'corosync configuration map access' (0) with my_member_list_entries = 2
1508158482.992382 notice  [SYNC  ] calling sync_process on service 
'corosync configuration map access' (0)
1508158482.992425 notice  [MAIN  ] executing 'corosync configuration map 
access' exec_handler_fn 0x56492b0cedf0 for node 1 (fn 0)
1508158482.992456 notice  [MAIN  ] executing 'corosync configuration map 
access' exec_handler_fn 0x56492b0cedf0 for node 2 (fn 0)
1508158482.992498 notice  [SYNC  ] calling sync_activate on service 
'corosync configuration map access' (0)
1508158482.992529 notice  [SYNC  ] calling sync_init on service 
'corosync cluster closed process group service v1.01' (1) with 
my_member_list_entries = 2
1508158482.992572 notice  [SYNC  ] calling sync_process on service 
'corosync cluster closed process group service v1.01' (1)
1508158482.992603 notice  [MAIN  ] executing 'corosync cluster closed 
process group service v1.01' exec_handler_fn 0x56492b0d2940 for node 2 
(fn 5)
1508158482.992646 notice  [MAIN  ] executing 'corosync cluster closed 
process group service v1.01' exec_handler_fn 0x56492b0d2940 for node 1 
(fn 5)
1508158482.992677 notice  [SYNC  ] calling sync_activate on service 
'corosync cluster closed process group service v1.01' (1)
1508158482.992720 notice  [SYNC  ] calling sync_init on service 
'corosync vote quorum service v1.0' (2) with my_member_list_entries = 2
1508158482.992750 notice  [VOTEQ ] votequorum_sync_init has 2 
member_list_entries
1508158482.992792 notice  [SYNC  ] calling sync_process on service 
'corosync vote quorum service v1.0' (2)
1508158482.992850 notice  [TOTEM ] A new membership (10.71.218.18:2388) 
was formed. Members left: 1
1508158482.992895 notice  [MAIN  ] executing 'corosync vote quorum 
service v1.0' exec_handler_fn 0x56492b0d6bf0 for node 2 (fn 0)
1508158482.992938 notice  [VOTEQ ] 
message_handler_req_exec_votequorum_nodeinfo (0x56492b0d6bf0) marking 
node 2 as MEMBER
1508158482.992968 notice  [VOTEQ ] get_total_votes: node 1 is a MEMBER 
so counting vote
1508158482.993011 notice  [VOTEQ ] get_total_votes: node 2 is a MEMBER 
so counting vote
1508158482.993042 notice  [MAIN  ] executing 'corosync vote quorum 
service v1.0' exec_handler_fn 0x56492b0d6bf0 for node 2 (fn 0)
1508158482.993084 notice  [SYNC  ] calling sync_init on service 
'corosync configuration map access' (0) with my_member_list_entries = 1
1508158482.993115 notice  [SYNC  ] calling sync_process on service 
'corosync configuration map access' (0)
1508158482.993157 notice  [MAIN  ] executing 'corosync configuration map 
access' exec_handler_fn 0x56492b0cedf0 for node 2 (fn 0)
1508158482.993188 notice  [SYNC  ] calling sync_activate on service 
'corosync configuration map access' (0)
1508158482.993231 notice  [SYNC  ] calling sync_init on service 
'corosync cluster closed process group service v1.01' (1) with 
my_member_list_entries = 1
1508158482.993261 notice  [SYNC  ] calling sync_process on service 
'corosync cluster closed process group service v1.01' (1)
1508158482.993304 notice  [MAIN  ] executing 'corosync cluster closed 
process group service v1.01' exec_handler_fn 0x56492b0d2940 for node 2 
(fn 5)
1508158482.993335 notice  [SYNC  ] calling sync_activate on service 
'corosync cluster closed process group service v1.01' (1)
1508158482.993378 notice  [SYNC  ] calling sync_init on service 
'corosync vote quorum service v1.0' (2) with my_member_list_entries = 1
1508158482.993409 notice  [VOTEQ ] votequorum_sync_init has 1 
member_list_entries
1508158482.993452 notice  [VOTEQ ] votequorum_sync_init marking node 1 
as DEAD
1508158482.993482 notice  [SYNC  ] calling sync_process on service 
'corosync vote quorum service v1.0' (2)
1508158482.993525 notice  [MAIN  ] executing 'corosync vote quorum 
service v1.0' exec_handler_fn 0x56492b0d6bf0 for node 2 (fn 0)
1508158482.993555 notice  [VOTEQ ] 
message_handler_req_exec_votequorum_nodeinfo (0x56492b0d6bf0) marking 
node 2 as MEMBER
1508158482.993598 notice  [VOTEQ ] get_total_votes: node 2 is a MEMBER 
so counting vote
1508158482.993628 notice  [MAIN  ] executing 'corosync vote quorum 
service v1.0' exec_handler_fn 0x56492b0d6bf0 for node 2 (fn 0)
1508158482.993673 notice  [SYNC  ] calling sync_activate on service 
'corosync vote quorum service v1.0' (2)
1508158482.993703 notice  [VOTEQ ] get_total_votes: node 2 is a MEMBER 
so counting vote
1508158482.993746 notice  [QUORUM] This node is within the non-primary 
component and will NOT provide any services.
1508158482.993776 notice  [QUORUM] Members[1]: 2
1508158482.993818 notice  [MAIN  ] Completed service synchronization, 
ready to provide service.

When it's working incorrectly:

1508158493.905246 notice  [TOTEM ] A new membership (10.71.218.17:2392) 
was formed. Members joined: 1
1508158493.905392 notice  [MAIN  ] executing 'corosync vote quorum 
service v1.0' exec_handler_fn 0x56492b0d6bf0 for node 1 (fn 0)
1508158493.905522 notice  [VOTEQ ] 
message_handler_req_exec_votequorum_nodeinfo (0x56492b0d6bf0) marking 
node 1 as MEMBER
1508158493.905623 notice  [VOTEQ ] get_total_votes: node 1 is a MEMBER 
so counting vote
1508158493.905697 notice  [VOTEQ ] get_total_votes: node 2 is a MEMBER 
so counting vote
1508158493.905742 notice  [QUORUM] This node is within the primary 
component and will provide service.
1508158493.905773 notice  [QUORUM] Members[1]: 2
1508158493.905815 notice  [SYNC  ] calling sync_init on service 
'corosync configuration map access' (0) with my_member_list_entries = 2
1508158493.905889 notice  [SYNC  ] calling sync_process on service 
'corosync configuration map access' (0)
1508158493.905921 notice  [MAIN  ] executing 'corosync configuration map 
access' exec_handler_fn 0x56492b0cedf0 for node 1 (fn 0)
1508158493.905951 notice  [MAIN  ] executing 'corosync configuration map 
access' exec_handler_fn 0x56492b0cedf0 for node 2 (fn 0)
1508158493.905993 notice  [SYNC  ] calling sync_activate on service 
'corosync configuration map access' (0)
1508158493.906023 notice  [SYNC  ] calling sync_init on service 
'corosync cluster closed process group service v1.01' (1) with 
my_member_list_entries = 2
1508158493.906066 notice  [SYNC  ] calling sync_process on service 
'corosync cluster closed process group service v1.01' (1)
1508158493.906096 notice  [MAIN  ] executing 'corosync cluster closed 
process group service v1.01' exec_handler_fn 0x56492b0d2940 for node 2 
(fn 5)
1508158493.906138 notice  [TOTEM ] A new membership (10.71.218.18:2396) 
was formed. Members left: 1
1508158493.906168 notice  [SYNC  ] calling sync_init on service 
'corosync configuration map access' (0) with my_member_list_entries = 1
1508158493.906210 notice  [SYNC  ] calling sync_process on service 
'corosync configuration map access' (0)
1508158493.906240 notice  [MAIN  ] executing 'corosync configuration map 
access' exec_handler_fn 0x56492b0cedf0 for node 2 (fn 0)
1508158493.906282 notice  [SYNC  ] calling sync_activate on service 
'corosync configuration map access' (0)
1508158493.906312 notice  [SYNC  ] calling sync_init on service 
'corosync cluster closed process group service v1.01' (1) with 
my_member_list_entries = 1
1508158493.906354 notice  [SYNC  ] calling sync_process on service 
'corosync cluster closed process group service v1.01' (1)
1508158493.906384 notice  [MAIN  ] executing 'corosync cluster closed 
process group service v1.01' exec_handler_fn 0x56492b0d2940 for node 2 
(fn 5)
1508158493.906427 notice  [SYNC  ] calling sync_activate on service 
'corosync cluster closed process group service v1.01' (1)
1508158493.906457 notice  [SYNC  ] calling sync_init on service 
'corosync vote quorum service v1.0' (2) with my_member_list_entries = 1
1508158493.906499 notice  [VOTEQ ] votequorum_sync_init has 1 
member_list_entries
1508158493.906528 notice  [SYNC  ] calling sync_process on service 
'corosync vote quorum service v1.0' (2)
1508158493.906570 notice  [MAIN  ] executing 'corosync vote quorum 
service v1.0' exec_handler_fn 0x56492b0d6bf0 for node 2 (fn 0)
1508158493.906600 notice  [VOTEQ ] 
message_handler_req_exec_votequorum_nodeinfo (0x56492b0d6bf0) marking 
node 2 as MEMBER
1508158493.906642 notice  [VOTEQ ] get_total_votes: node 1 is a MEMBER 
so counting vote
1508158493.906672 notice  [VOTEQ ] get_total_votes: node 2 is a MEMBER 
so counting vote
1508158493.906714 notice  [MAIN  ] executing 'corosync vote quorum 
service v1.0' exec_handler_fn 0x56492b0d6bf0 for node 2 (fn 0)
1508158493.906743 notice  [SYNC  ] calling sync_activate on service 
'corosync vote quorum service v1.0' (2)
1508158493.906785 notice  [VOTEQ ] get_total_votes: node 1 is a MEMBER 
so counting vote
1508158493.906815 notice  [VOTEQ ] get_total_votes: node 2 is a MEMBER 
so counting vote
1508158493.906856 notice  [QUORUM] Members[1]: 2
1508158493.906886 notice  [MAIN  ] Completed service synchronization, 
ready to provide service.

Now it seems that sync calls votequorum's exec_handler_fn in both 
working and non-working cases. So now it relies on votequorum_sync_init 
being called once with both members and once without node 1 in order to 
set the node as NODESTATE_DEAD.

Thanks,
Jonathan




More information about the Users mailing list