Bug 1427387

+++ This bug was initially created as a clone of Bug #1421938 +++

+++ This bug was initially created as a clone of Bug #1415178 +++

Description of problem:
=====================
I am seeing lot of ping time outs on my systemic setup clients as below
[2017-01-20 08:07:53.591156] C [rpc-clnt-ping.c:160:rpc_clnt_ping_timer_expired] 0-systemic-client-6: server 10.70.35.156:49153 has not responded in the last 42 seconds, disconnecting.
[2017-01-20 08:07:53.595238] W [rpc-clnt-ping.c:203:rpc_clnt_ping_cbk] 0-systemic-client-6: socket disconnected
[2017-01-20 08:32:58.781026] C [rpc-clnt-ping.c:160:rpc_clnt_ping_timer_expired] 0-systemic-client-2: server 10.70.35.156:49152 has not responded in the last 42 seconds, disconnecting.
[2017-01-20 08:32:58.818598] W [rpc-clnt-ping.c:203:rpc_clnt_ping_cbk] 0-systemic-client-2: socket disconnected
[2017-01-20 08:35:31.801622] C [rpc-clnt-ping.c:160:rpc_clnt_ping_timer_expired] 0-systemic-client-7: server 10.70.37.154:49153 has not responded in the last 42 seconds, disconnecting.
[2017-01-20 08:35:31.802349] W [rpc-clnt-ping.c:203:rpc_clnt_ping_cbk] 0-systemic-client-7: socket disconnected
[2017-01-20 08:39:22.835813] C [rpc-clnt-ping.c:160:rpc_clnt_ping_timer_expired] 0-systemic-client-7: server 10.70.37.154:49153 has not responded in the last 42 seconds, disconnecting.
[2017-01-20 08:39:22.841445] W [rpc-clnt-ping.c:203:rpc_clnt_ping_cbk] 0-systemic-client-7: socket disconnected
[2017-01-20 08:52:28.949400] C [rpc-clnt-ping.c:160:rpc_clnt_ping_timer_expired] 0-systemic-client-3: server 10.70.37.154:49152 has not responded in the last 42 seconds, disconnecting.
[2017-01-20 08:52:28.950309] W [rpc-clnt-ping.c:203:rpc_clnt_ping_cbk] 0-systemic-client-3: socket disconnected
[2017-01-20 09:11:15.090477] C [rpc-clnt-ping.c:160:rpc_clnt_ping_timer_expired] 0-systemic-client-7: server 10.70.37.154:49153 has not responded in the last 42 seconds, disconnecting.
[2017-01-20 09:11:15.091079] W [rpc-clnt-ping.c:203:rpc_clnt_ping_cbk] 0-systemic-client-7: socket disconnected
[2017-01-20 09:15:03.122268] C [rpc-clnt-ping.c:160:rpc_clnt_ping_timer_expired] 0-systemic-client-7: server 10.70.37.154:49153 has not responded in the last 42 seconds, disconnecting.
[2017-01-20 09:15:03.125457] W [rpc-clnt-ping.c:203:rpc_clnt_ping_cbk] 0-systemic-client-7: socket disconnected
[2017-01-20 09:17:28.141896] C [rpc-clnt-ping.c:160:rpc_clnt_ping_timer_expired] 0-systemic-client-6: server 10.70.35.156:49153 has not responded in the last 42 seconds, disconnecting.
[2017-01-20 09:17:28.146266] W [rpc-clnt-ping.c:203:rpc_clnt_ping_cbk] 0-systemic-client-6: socket disconnected
[2017-01-20 09:36:10.260003] C [rpc-clnt-ping.c:160:rpc_clnt_ping_timer_expired] 0-systemic-client-2: server 10.70.35.156:49152 has not responded in the last 42 seconds, disconnecting.
[2017-01-20 09:36:10.329709] W [rpc-clnt-ping.c:203:rpc_clnt_ping_cbk] 0-systemic-client-2: socket disconnected
[2017-01-20 09:39:02.283174] C [rpc-clnt-ping.c:160:rpc_clnt_ping_timer_expired] 0-systemic-client-3: server 10.70.37.154:49152 has not responded in the last 42 seconds, disconnecting.
[2017-01-20 09:39:02.283875] W [rpc-clnt-ping.c:203:rpc_clnt_ping_cbk] 0-systemic-client-3: socket disconnected
[2017-01-20 09:42:15.311267] C [rpc-clnt-ping.c:160:rpc_clnt_ping_timer_expired] 0-systemic-client-7: server 10.70.37.154:49153 has not responded in the last 42 seconds, disconnecting.
[2017-01-20 09:42:15.311701] W [rpc-clnt-ping.c:203:rpc_clnt_ping_cbk] 0-systemic-client-7: socket disconnected



This would eventually lead to splitbrains which is not a good place to be in


Version-Release number of selected component (if applicable):
==========
3.8.4-12

--- Additional comment from Raghavendra G on 2017-01-23 00:17:07 EST ---

I've some queries:

* what was the disk utilization during testing?
* Can you please get profile info of bricks? I need to see what operations are being performed and their frequency.
* Is it possible to get strace of brick process when tests are being run? You can use following cmdline:
strace -ff -T -p <pid-of-brick> -o <path-where-you-want-the-strace-output-saved>

Following is a possible hypothesis

<hypothesis>

server not able to read ping request.

Me, Kritika and Pranith were about an issue where they had hit ping timer expiry in replicated setups when disk usage was high. The reason for this as Pranith pointed out was,
1. posix has some fops (like posix_xattrop, posix_fxattrop) which do syscalls after holding a lock on inode (inode->lock).
2. During high disk usage scenarios, syscall latencies were high (sometimes >= ping-timeout value)
3. Before being handed over to a new thread at io-threads xlator, a fop gets executed in one of the threads that reads incoming messages from socket. This execution path includes some translators like protocol/server, index, quota-enforcer, marker. And these translators might access inode-ctx which involves locking inode (inode->lock). Due to this locking latency of syscall gets transferred to poller thread. Since poller thread is waiting on inode->lock, it won't be able to read ping requests from network in-time resulting in ping-timer expiry.

</hypothesis>

--- Additional comment from Raghavendra G on 2017-01-25 06:59:41 EST ---

I went through strace output and volume profile. Though volume profile shows large max latencies for fops like xattrop/fxattrop, syscall latencies shown by strace is not too much to cause a ping timeout. As to large xattrop/fxattrop latency, the fops are serialized and when there too many (f)xattrops on the same file, the last fop can have a latency which is cumulative of all the (f)xattrops in the waiting queue before it. So, its not really an issue.

Nag also informed me that the disk utilization was not high when ping-timeout happened. So, I doubt whether its high disk utilization that caused this ping-timeout.

ATM, I don't have an RCA, but we can experiment with two things:
1. Increase the poller threads to 8 on bricks
2. Use fix [1]

Note that both the above two steps need to be done before starting tests.

[1] https://review.gluster.org/15046

--- Additional comment from Mohit Agrawal on 2017-01-27 03:13:56 EST ---

Hi,

 Can you please confirm about reproducer steps? As per doc It seems below are the steps 

 1) Run the script to create deep directory structure (5 Level) from two different client
 2) Run untar/tar linux.tar command operation 50 times in directory 

Regards
Mohit Agrawal

--- Additional comment from nchilaka on 2017-01-31 01:25:22 EST ---

yes, along with that taking of statedumps at regular intervals for both clients and servers.

--- Additional comment from Raghavendra G on 2017-01-31 23:39:39 EST ---

Nag,

Let me know once the setup becomes free. We would like to gather more diagnostic information. Machine and login details would help us to continue debugging the issue.

regards,
Raghavendra

--- Additional comment from Raghavendra G on 2017-02-01 07:07:40 EST ---

Another thing to verify is whether the vms running bricks and client themselves are pausing. If they are pausing for more than ping-timeout duration, that can be a simple cause for ping-timer-expiry.

--- Additional comment from Mohit Agrawal on 2017-02-02 00:21:13 EST ---

Hi,


I tried to reproduce the issue as step mentioned in previous comment but i did not get success.
I have checked on the setup (server 10.70.35.20), vm is accesible but it seems all resources(cpu,memory) are consumed and even i am not able to run any linux command on vm.

On the client side below message are continuously coming in logs  

[2017-02-02 05:26:23.661141] I [rpc-clnt.c:1965:rpc_clnt_reconfig] 0-systemic-client-4: changing port to 49153 (from 0)
[2017-02-02 05:26:23.667104] E [socket.c:2309:socket_connect_finish] 0-systemic-client-4: connection to 10.70.35.20:49153 failed (Connection refused)


Ping timeout issue could be happen if brick process is not able to respond within time period (42 second) and brick is not able to respond because sufficient resources are not available on vm.


Regards
Mohit Agrawal

--- Additional comment from nchilaka on 2017-02-09 01:17:08 EST ---

i had shared the setup.
hence removing needinfo

--- Additional comment from Worker Ant on 2017-02-14 01:36:01 EST ---

REVIEW: https://review.gluster.org/16462 (storage/posix: Execute syscalls in xattrop under different locks) posted (#4) for review on master by Krutika Dhananjay (kdhananj)

--- Additional comment from Worker Ant on 2017-02-27 03:26:45 EST ---

COMMIT: https://review.gluster.org/16462 committed in master by Pranith Kumar Karampuri (pkarampu) 
------
commit b5c26a462caf97bfc5380c81092f5c331ccaf1ae
Author: Krutika Dhananjay <kdhananj>
Date:   Mon Jan 23 17:40:40 2017 +0530

    storage/posix: Execute syscalls in xattrop under different locks
    
    ... and not inode->lock. This is to prevent the epoll thread from
    *potentially* being blocked on this lock in the worst case for
    extended period elsewhere in the brick stack, while the syscalls
    in xattrop are being performed under the same lock by a different
    thread. This could potentially lead to ping-timeout, if the only
    available epoll thread is busy waiting on the inode->lock, thereby
    preventing it from picking up the ping request from the client(s).
    
    Also removed some unused functions.
    
    Change-Id: I2054a06701ecab11aed1c04e80ee57bbe2e52564
    BUG: 1421938
    Signed-off-by: Krutika Dhananjay <kdhananj>
    Reviewed-on: https://review.gluster.org/16462
    Smoke: Gluster Build System <jenkins.org>
    NetBSD-regression: NetBSD Build System <jenkins.org>
    Reviewed-by: Raghavendra G <rgowdapp>
    CentOS-regression: Gluster Build System <jenkins.org>

--- Additional comment from Raghavendra G on 2017-02-27 23:30:44 EST ---

Moving back to POST as we've to RCA whether there are other reasons why ping-timeout might've happened.