Re: [PATCH] mon: use first_commited instead of latest_full map if latest_bl.length() == 0

[Joao Eduardo Luis <joao.luis@inktank.com>]

On 07/19/2013 09:31 AM, Stefan Priebe wrote:
> this fixes a failure like:
>       0> 2013-07-19 09:29:16.803918 7f7fb5f31780 -1 mon/OSDMonitor.cc: In function 'virtual void OSDMonitor::update_from_paxos(bool*)' thread 7f7fb5f31780 time 2013-07-19 09:29:16.803439
> mon/OSDMonitor.cc: 132: FAILED assert(latest_bl.length() != 0)
>
>   ceph version 0.61.5-15-g72c7c74 (72c7c74e1f160e6be39b6edf30bce09b770fa777)
>   1: (OSDMonitor::update_from_paxos(bool*)+0x16e1) [0x51d121]
>   2: (PaxosService::refresh(bool*)+0xe6) [0x4f2a46]
>   3: (Monitor::refresh_from_paxos(bool*)+0x57) [0x48f7b7]
>   4: (Monitor::init_paxos()+0xe5) [0x48f955]
>   5: (Monitor::preinit()+0x679) [0x4b1cf9]
>   6: (main()+0x36b0) [0x484bb0]
>   7: (__libc_start_main()+0xfd) [0x7f7fb408dc8d]
>   8: /usr/bin/ceph-mon() [0x4801e9]
>   NOTE: a copy of the executable, or `objdump -rdS <executable>` is needed to interpret this.
> ---
>   src/mon/OSDMonitor.cc |    6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/src/mon/OSDMonitor.cc b/src/mon/OSDMonitor.cc
> index 9c854cd..ab3b8ec 100644
> --- a/src/mon/OSDMonitor.cc
> +++ b/src/mon/OSDMonitor.cc
> @@ -129,6 +129,12 @@ void OSDMonitor::update_from_paxos(bool *need_bootstrap)
>     if ((latest_full > 0) && (latest_full > osdmap.epoch)) {
>       bufferlist latest_bl;
>       get_version_full(latest_full, latest_bl);
> +
> +    if (latest_bl.length() == 0 && latest_full != 0 && get_first_committed() > 1) {

latest_full is always > 0 here, following the previous if check.

> +        dout(0) << __func__ << " latest_bl.length() == 0 use first_commited instead of latest_full" << dendl;
> +        latest_full = get_first_committed();
> +        get_version_full(latest_full, latest_bl);
> +    }
>       assert(latest_bl.length() != 0);
>       dout(7) << __func__ << " loading latest full map e" << latest_full << dendl;
>       osdmap.decode(latest_bl);
>

Although appreciated, this patch fixes the symptom leading to the crash. 
  The bug itself seems to be that there is a latest_full version that is 
empty.  Until we know for sure what is happening and what is leading to 
such state, fixing the symptom is not advisable, as it is not only 
masking the real issue but it may also have unforeseen long-term effects.

Stefan, do you still have the store state on which this was triggered? 
If so, can you share it with us (or dig a bit into it yourself if you 
can't share the store, in which case I'll let you know what to look for).

   -Joao


-- 
Joao Eduardo Luis
Software Engineer | http://inktank.com | http://ceph.com