osd/ReplicatedPG.cc: 7110: FAILED assert(head != hobject_t())

 ceph version 0.56.1 (e4a541624df62ef353e754391cbbb707f54b16f7)
 1: (ReplicatedPG::_scrub(ScrubMap&)+0x1d46) [0x652c46]
 2: (PG::scrub_compare_maps()+0x1357) [0x74c497]
 3: (PG::chunky_scrub()+0x307) [0x74d347]
 4: (PG::scrub()+0x135) [0x74ed45]
 5: (OSD::ScrubWQ::_process(PG*)+0xc) [0x6e648c]
 6: (ThreadPool::worker(ThreadPool::WorkThread*)+0x95c) [0x8d234c]
 7: (ThreadPool::WorkThread::entry()+0x10) [0x8d32c0]
 8: (()+0x7e9a) [0x7fa9f0178e9a]
 9: (clone()+0x6d) [0x7fa9eebf5cbd]
 NOTE: a copy of the executable, or `objdump -rdS <executable>` is needed to interpret this.

--- begin dump of recent events ---
-100000> 2013-01-11 17:17:10.899804 7fa9e135c700  1 -- 149.165.228.10:6804/27184 --> 149.165.228.11:0/9685 -- osd_ping(ping_reply e4374 stamp 2013-01-11 17:17:10.908240) v2 -- ?+0 0x8d20000 con 0x97a2840
-99999> 2013-01-11 17:17:10.899830 7fa9e135c700 20 osd.0 4374 _share_map_outgoing 0x7c58c60 already has epoch 4374
-99998> 2013-01-11 17:17:10.922778 7fa9ddb55700 10 filestore(/data/osd.0) FileStore::read 2.1ac_head/3d3be9ac/rb.0.1e3e.238e1f29.00000000b261/head//2 1572864~524288/524288
-99997> 2013-01-11 17:17:10.923378 7fa9ddb55700 15 filestore(/data/osd.0) read 2.1ac_head/3d3be9ac/rb.0.1e3e.238e1f29.00000000b261/head//2 2097152~524288
-99996> 2013-01-11 17:17:10.923514 7fa9ddb55700 10 filestore(/data/osd.0) FileStore::read 2.1ac_head/3d3be9ac/rb.0.1e3e.238e1f29.00000000b261/head//2 2097152~524288/524288
-99995> 2013-01-11 17:17:10.923942 7fa9ddb55700 15 filestore(/data/osd.0) read 2.1ac_head/3d3be9ac/rb.0.1e3e.238e1f29.00000000b261/head//2 2621440~524288
-99994> 2013-01-11 17:17:10.924062 7fa9ddb55700 10 filestore(/data/osd.0) FileStore::read 2.1ac_head/3d3be9ac/rb.0.1e3e.238e1f29.00000000b261/head//2 2621440~524288/524288
-99993> 2013-01-11 17:17:10.924488 7fa9ddb55700 15 filestore(/data/osd.0) read 2.1ac_head/3d3be9ac/rb.0.1e3e.238e1f29.00000000b261/head//2 3145728~524288
-99992> 2013-01-11 17:17:10.933965 7fa9ddb55700 10 filestore(/data/osd.0) FileStore::read 2.1ac_head/3d3be9ac/rb.0.1e3e.238e1f29.00000000b261/head//2 3145728~524288/524288
-99991> 2013-01-11 17:17:10.934520 7fa9ddb55700 15 filestore(/data/osd.0) read 2.1ac_head/3d3be9ac/rb.0.1e3e.238e1f29.00000000b261/head//2 3670016~524288
-99990> 2013-01-11 17:17:10.934660 7fa9ddb55700 10 filestore(/data/osd.0) FileStore::read 2.1ac_head/3d3be9ac/rb.0.1e3e.238e1f29.00000000b261/head//2 3670016~524288/524288
-99989> 2013-01-11 17:17:10.935099 7fa9ddb55700 15 filestore(/data/osd.0) read 2.1ac_head/3d3be9ac/rb.0.1e3e.238e1f29.00000000b261/head//2 4194304~524288
-99988> 2013-01-11 17:17:10.935163 7fa9ddb55700 10 filestore(/data/osd.0) FileStore::read 2.1ac_head/3d3be9ac/rb.0.1e3e.238e1f29.00000000b261/head//2 4194304~0/524288
-99987> 2013-01-11 17:17:10.935222 7fa9ddb55700 10 filestore(/data/osd.0) stat 2.1ac_head/c322f9ac/rb.0.1b07.238e1f29.000000008b3a/head//2 = 0 (size 4194304)
-99986> 2013-01-11 17:17:10.935229 7fa9ddb55700 15 filestore(/data/osd.0) getattrs 2.1ac_head/c322f9ac/rb.0.1b07.238e1f29.000000008b3a/head//2
-99985> 2013-01-11 17:17:10.935286 7fa9ddb55700 20 filestore(/data/osd.0) fgetattrs 45 getting '_'
-99984> 2013-01-11 17:17:10.935302 7fa9ddb55700 20 filestore(/data/osd.0) fgetattrs 45 getting 'snapset'
-99983> 2013-01-11 17:17:10.935309 7fa9ddb55700 10 filestore(/data/osd.0) getattrs 2.1ac_head/c322f9ac/rb.0.1b07.238e1f29.000000008b3a/head//2 = 0
-99982> 2013-01-11 17:17:10.935313 7fa9ddb55700 15 filestore(/data/osd.0) read 2.1ac_head/c322f9ac/rb.0.1b07.238e1f29.000000008b3a/head//2 0~524288
-99981> 2013-01-11 17:17:10.985207 7fa9ddb55700 10 filestore(/data/osd.0) FileStore::read 2.1ac_head/c322f9ac/rb.0.1b07.238e1f29.000000008b3a/head//2 0~524288/524288