[Gluster-users] gnfs split brain when 1 server in 3x1 down (high load) - help request

[Ravishankar N]

afr_final_errno() is called from many other places other than the inode 
refresh code path, so the 2 (ENOENT) could be from one of those (mostly 
afr_lookup_done) but it is puzzling that you are not seeing EIO even 
once when it is called from afr_inode_refresh_subvol_cbk() code path. 
Not sure what is happening here.

On 06/04/20 6:52 am, Erik Jacobson wrote:
> During the problem case, near as I can tell, afr_final_errno(),
> in the loop where tmp_errno = local->replies[i].op_errno is set,
> the errno is always "2" when it gets to that point on server 3 (where
> the NFS load is).
>
> I never see a value other than 2.
>
> I later simply put the print at the end of the function too, to double
> verify non-zero exit codes. There are thousands of non-zero return
> codes, all 2 when not zero. Here is an exmaple flow right before a
> split-brain. I do not wish to imply the split-brain is related, it's
> just an example log snip:
>
>
> [2020-04-06 00:54:21.125373] E [MSGID: 0] [afr-common.c:2546:afr_final_errno] 0-erikj-afr_final_errno: erikj dbg afr_final_errno() errno from loop before afr_higher_errno was: 2
> [2020-04-06 00:54:21.125374] E [MSGID: 0] [afr-common.c:2551:afr_final_errno] 0-erikj-afr_final_errno: erikj dbg returning non-zero: 2
> [2020-04-06 00:54:23.315397] E [MSGID: 0] [afr-read-txn.c:283:afr_read_txn_refresh_done] 0-cm_shared-replicate-0: erikj dbg crapola 1st if in afr_read_txn_refresh_done() !priv->thin_arbiter_count -- goto to readfn
> [2020-04-06 00:54:23.315432] E [MSGID: 108008] [afr-read-txn.c:314:afr_read_txn_refresh_done] 0-cm_shared-replicate-0: Failing READLINK on gfid 57f269ef-919d-40ec-b7fc-a7906fee648b: split-brain observed. [Input/output error]
> [2020-04-06 00:54:23.315450] W [MSGID: 112199] [nfs3-helpers.c:3327:nfs3_log_readlink_res] 0-nfs-nfsv3: /image/images_ro_nfs/rhel8.0/usr/lib64/libmlx5.so.1 => (XID: 1fdba2bc, READLINK: NFS: 5(I/O error), POSIX: 5(Input/output error)) target: (null)
>
>
> I am missing something. I will see if Scott and I can work together
> tomorrow. Happy for any more ideas, Thank you!!
>
>
> On Sun, Apr 05, 2020 at 06:49:56PM -0500, Erik Jacobson wrote:
>> First, it's possible our analysis is off somewhere. I never get to your
>> print message. I put a debug statement at the start of the function so I
>> know we get there (just to verify my print statements were taking
>> affect).
>>
>> I put a print statement for the if (call_count == 0) { call there, right
>> after the if. I ran some tests.
>>
>> I suspect that isn't a problem area. There were some interesting results
>> with an NFS stale file handle error going through that path. Otherwise
>> it's always errno=0 even in the heavy test case. I'm not concerned about
>> a stale NFS file handle this moment. That print was also hit heavily when
>> one server was down (which surprised me but I don't know the internals).
>>
>> I'm trying to re-read and work through Scott's message to see if any
>> other print statements might be helpful.
>>
>> Thank you for your help so far. I will reply back if I find something.
>> Otherwise suggestions welcome!
>>
>> The MFG system I can access got smaller this weekend but is still large
>> enough to reproduce the error.
>>
>> As you can tell, I work mostly at a level well above filesystem code so
>> thank you for staying with me as I struggle through this.
>>
>> Erik
>>
>>> After we hear from all children, afr_inode_refresh_subvol_cbk() then calls afr_inode_refresh_done()-->afr_txn_refresh_done()-->afr_read_txn_refresh_done().
>>> But you already know this flow now.
>>> diff --git a/xlators/cluster/afr/src/afr-common.c b/xlators/cluster/afr/src/afr-common.c
>>> index 4bfaef9e8..096ce06f0 100644
>>> --- a/xlators/cluster/afr/src/afr-common.c
>>> +++ b/xlators/cluster/afr/src/afr-common.c
>>> @@ -1318,6 +1318,12 @@ afr_inode_refresh_subvol_cbk(call_frame_t *frame, void *cookie, xlator_t *this,
>>>           if (xdata)
>>>               local->replies[call_child].xdata = dict_ref(xdata);
>>>       }
>>> +    if (op_ret == -1)
>>> +        gf_msg_callingfn(
>>> +            this->name, GF_LOG_ERROR, op_errno, AFR_MSG_SPLIT_BRAIN,
>>> +            "Inode refresh on child:%d failed with errno:%d for %s(%s) ",
>>> +            call_child, op_errno, local->loc.name,
>>> +            uuid_utoa(local->loc.inode->gfid));
>>>       if (xdata) {
>>>           ret = dict_get_int8(xdata, "link-count", &need_heal);
>>>           local->replies[call_child].need_heal = need_heal;
>