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BLueStore Deadlock

Message ID BL2PR02MB2115A9ED532BA7728F44A02AF4180@BL2PR02MB2115.namprd02.prod.outlook.com (mailing list archive)
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Commit Message

Somnath Roy Aug. 5, 2016, 2:14 a.m. UTC 
Sorry for the delay ,
Jianpeng,
Could you please try the following pull request in your setup and see if the deadlock is still happening ?

https://github.com/ceph/ceph/pull/10578

Mark,
I think it has the probable fix for your crash in onode->flush() as well , could you please try this out ?

Thanks & Regards
Somnath

-----Original Message-----
From: Ma, Jianpeng [mailto:jianpeng.ma@intel.com] 
Sent: Tuesday, August 02, 2016 6:35 PM
To: Sage Weil
Cc: ceph-devel; Somnath Roy
Subject: RE: BLueStore Deadlock

Hi Sage:
    Why is there STATE_WRITTING? 
  In my option: for normal read, it do onode->flush() , so no need wait io complete. The special case is one transaction which has two write and later write need read.
  For write, if it is wal-write, when do finish_write, the data don't locate into disk. This different with non-wal-write

Thanks! 
  

-----Original Message-----
From: Ma, Jianpeng 
Sent: Friday, July 29, 2016 9:36 AM
To: Ma, Jianpeng <jianpeng.ma@intel.com>; Somnath Roy <Somnath.Roy@sandisk.com>
Cc: ceph-devel <ceph-devel@vger.kernel.org>
Subject: RE: BLueStore Deadlock

Roy: my question is why is there STATE_WRITTING?  For read we don't by pass cache, so why need STATE_WRITTING?

Thanks!

-----Original Message-----
From: ceph-devel-owner@vger.kernel.org [mailto:ceph-devel-owner@vger.kernel.org] On Behalf Of Ma, Jianpeng
Sent: Friday, July 29, 2016 9:24 AM
To: Somnath Roy <Somnath.Roy@sandisk.com>
Cc: ceph-devel <ceph-devel@vger.kernel.org>
Subject: RE: BLueStore Deadlock

Hi Roy:
    W/ your patch, there still deadlock.
By the way, if we change the BufferSpace::_add_buffer, if w/ cache flush push it into cache front and if w/o cache flag only put it  at back.
I think use this way we can remove finish_write.
How about it?

Thanks!

-----Original Message-----
From: ceph-devel-owner@vger.kernel.org [mailto:ceph-devel-owner@vger.kernel.org] On Behalf Of Somnath Roy
Sent: Friday, July 29, 2016 6:22 AM
To: Ma, Jianpeng <jianpeng.ma@intel.com>
Cc: ceph-devel <ceph-devel@vger.kernel.org>
Subject: RE: BLueStore Deadlock

Jianpeng,
I thought through this and it seems there could be one possible deadlock scenario.

tp_osd_tp --> waiting on onode->flush() for previous txc to finish. Holding Wlock(coll) aio_complete_thread --> waiting for RLock(coll) No other thread will be blocked here.

We do add previous txc in the flush_txns list during _txc_write_nodes() and before aio_complete_thread calling _txc_state_proc(). So, if within this time frame if we have IO on the same collection , it will be waiting on unfinished txcs.
The solution to this could be the following..

root@emsnode5:~/ceph-master/src# git diff diff --git a/src/os/bluestore/BlueStore.cc b/src/os/bluestore/BlueStore.cc index e8548b1..575a234 100644
I am not able to reproduce this in my setup , so, if you can do the above changes in your env and see if you are still hitting the issue, would be helpful.

Thanks & Regards
Somnath


-----Original Message-----
From: Somnath Roy
Sent: Thursday, July 28, 2016 8:45 AM
To: 'Ma, Jianpeng'
Cc: ceph-devel
Subject: RE: BLueStore Deadlock

Hi Jianpeng,
Are you trying with latest master and still hitting the issue (seems so but confirming) ?
The following scenario should not be creating deadlock because of the following reason.

Onode->flush() is waiting on flush_lock() and from _txc_finish() it is releasing that before taking osr->qlock(). Am I missing anything ?

I got a deadlock in this path in one of my earlier changes in the following pull request (described in detail there) and it is fixed and merged.

https://github.com/ceph/ceph/pull/10220

If my theory is right , we are hitting deadlock because of some other reason may be. It seems you are doing WAL write , could you please describe the steps to reproduce ?

Thanks & Regards
Somnath

From: Ma, Jianpeng [mailto:jianpeng.ma@intel.com]
Sent: Thursday, July 28, 2016 1:46 AM
To: Somnath Roy
Cc: ceph-devel; Ma, Jianpeng
Subject: BLueStore Deadlock

Hi Roy:
     When do seqwrite w/ rbd+librbd, I met deadlock for bluestore. It can reproduce 100%.(based on 98602ae6c67637dbadddd549bd9a0035e5a2717)
By add message and this found this bug caused by bf70bcb6c54e4d6404533bc91781a5ef77d62033.
Consider this case:

tp_osd_tp                                              aio_complete_thread                                 kv_sync_thread
Rwlock(coll)                                            txc_finish_io                                                     _txc_finish do_write                                                 lock(osr->qlock)                                               lock(osr->qlock) do_read                                                  RLock(coll)                                                                     need osr->qlock to continue
onode->flush()                                            need coll
onode->readlock to continue
   need previous txc complete

But current I don't how to fix this.

Thanks!
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diff mbox

Patch

--- a/src/os/bluestore/BlueStore.cc
+++ b/src/os/bluestore/BlueStore.cc
@@ -4606,6 +4606,11 @@  void BlueStore::_txc_state_proc(TransContext *txc)
         (txc->first_collection)->lock.get_read();
       }
       for (auto& o : txc->onodes) {
+        {
+          std::lock_guard<std::mutex> l(o->flush_lock);
+          o->flush_txns.insert(txc);
+        }
+
         for (auto& p : o->blob_map.blob_map) {
            p.bc.finish_write(txc->seq);
        }
@@ -4733,8 +4738,8 @@  void BlueStore::_txc_write_nodes(TransContext *txc, KeyValueDB::Transaction t)
     dout(20) << "  onode " << (*p)->oid << " is " << bl.length() << dendl;
     t->set(PREFIX_OBJ, (*p)->key, bl);

-    std::lock_guard<std::mutex> l((*p)->flush_lock);
-    (*p)->flush_txns.insert(txc);
+    /*std::lock_guard<std::mutex> l((*p)->flush_lock);
+    (*p)->flush_txns.insert(txc);*/
   }