[Ocfs2-devel] [patch 03/10] ocfs2: o2net: don't shutdown connection when idle timeout

[Junxiao Bi]

Hi Mark,

Thanks for reviewing the patch.
See comments below.

On 08/14/2014 02:59 AM, Mark Fasheh wrote:
> On Wed, Aug 06, 2014 at 01:32:04PM -0700, Andrew Morton wrote:
>> From: Junxiao Bi <junxiao.bi at oracle.com>
>> Subject: ocfs2: o2net: don't shutdown connection when idle timeout
>>
>> This patch series is to fix a possible message lost bug in ocfs2 when
>> network go bad.  This bug will cause ocfs2 hung forever even network
>> become good again.
>>
>> The messages may lost in this case.  After the tcp connection is
>> established between two nodes, an idle timer will be set to check its
>> state periodically, if no messages are received during this time, idle
>> timer will timeout, it will shutdown the connection and try to reconnect,
>> so pending messages in tcp queues will be lost.  This messages may be from
>> dlm.  Dlm may get hung in this case.  This may cause the whole ocfs2
>> cluster hung.  
>>
>> This is very possible to happen when network state goes bad.  Do the
>> reconnect is useless, it will fail if network state is still bad.  Just
>> waiting there for network recovering may be a good idea, it will not lost
>> messages and some node will be fenced until cluster goes into split-brain
>> state, for this case, Tcp user timeout is used to override the tcp
>> retransmit timeout.  It will timeout after 25 days, user should have
>> notice this through the provided log and fix the network, if they don't,
>> ocfs2 will fall back to original reconnect way.
>>
>>
>>
>> This patch (of 3):
>>
>> Some messages in the tcp queue maybe lost if we shutdown the connection
>> and reconnect when idle timeout.  If packets lost and reconnect success,
>> then the ocfs2 cluster maybe hung.
>>
>> To fix this, we can leave the connection there and do the fence decision
>> when idle timeout, if network recover before fence dicision is made, the
>> connection survive without lost any messages.
>>
>> This bug can be saw when network state go bad.  It may cause ocfs2 hung
>> forever if some packets lost.  With this fix, ocfs2 will recover from hung
>> if network becomes good again.
>>
>> Signed-off-by: Junxiao Bi <junxiao.bi at oracle.com>
>> Reviewed-by: Srinivas Eeda <srinivas.eeda at oracle.com>
>> Cc: Mark Fasheh <mfasheh at suse.com>
>> 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/tcp.c |   25 +++++++++++++++++++------
>>  1 file changed, 19 insertions(+), 6 deletions(-)
>>
>> diff -puN fs/ocfs2/cluster/tcp.c~ocfs2-o2net-dont-shutdown-connection-when-idle-timeout fs/ocfs2/cluster/tcp.c
>> --- a/fs/ocfs2/cluster/tcp.c~ocfs2-o2net-dont-shutdown-connection-when-idle-timeout
>> +++ a/fs/ocfs2/cluster/tcp.c
>> @@ -1536,16 +1536,20 @@ static void o2net_idle_timer(unsigned lo
>>  #endif
>>  
>>  	printk(KERN_NOTICE "o2net: Connection to " SC_NODEF_FMT " has been "
>> -	       "idle for %lu.%lu secs, shutting it down.\n", SC_NODEF_ARGS(sc),
>> -	       msecs / 1000, msecs % 1000);
>> +	       "idle for %lu.%lu secs.\n",
>> +	       SC_NODEF_ARGS(sc), msecs / 1000, msecs % 1000);
>>  
>> -	/*
>> -	 * Initialize the nn_timeout so that the next connection attempt
>> -	 * will continue in o2net_start_connect.
>> +	/* idle timerout happen, don't shutdown the connection, but
>> +	 * make fence decision. Maybe the connection can recover before
>> +	 * the decision is made.
>>  	 */
>>  	atomic_set(&nn->nn_timeout, 1);
>> +	o2quo_conn_err(o2net_num_from_nn(nn));
>> +	queue_delayed_work(o2net_wq, &nn->nn_still_up,
>> +			msecs_to_jiffies(O2NET_QUORUM_DELAY_MS));
>> +
>> +	o2net_sc_reset_idle_timer(sc);
>>  
>> -	o2net_sc_queue_work(sc, &sc->sc_shutdown_work);
>>  }
>>  
>>  static void o2net_sc_reset_idle_timer(struct o2net_sock_container *sc)
>> @@ -1560,6 +1564,15 @@ static void o2net_sc_reset_idle_timer(st
>>  
>>  static void o2net_sc_postpone_idle(struct o2net_sock_container *sc)
>>  {
>> +	struct o2net_node *nn = o2net_nn_from_num(sc->sc_node->nd_num);
>> +
>> +	/* clear fence decision since the connection recover from timeout*/
>> +	if (atomic_read(&nn->nn_timeout)) {
>> +		o2quo_conn_up(o2net_num_from_nn(nn));
>> +		cancel_delayed_work(&nn->nn_still_up);
> This might sound silly (since there's a chance the node is killed) but what
> about the return value of cancel_delayed_work() here? There's a chance the
> delayed work couldn't be canceled, does that impact the patch in any
> negative manner?
The return value don't need to be taken care.
Two cases:
1) If the work is still pending, then the function will cancel it and
return true.
    no problem.
2) If the work is running, the function will return false. If cluster is
in split-brain,
then the work will do nothing, else this node will be fenced, this means
the net
revert too late. So this case also can't affect the following patch manner.

Thanks,
Junxiao.
>
> Thanks,
> 	--Mark
>
> --
> Mark Fasheh