One of our primary instances failed after a segfault :

2014-12-12T22:24:22.411+0100 [conn107448] SEVERE: Invalid access at address: 0
2014-12-12T22:24:22.491+0100 [conn107448] SEVERE: Got signal: 11 (Segmentation fault).
Backtrace:0x11da801 0x11d9bde 0x11d9ccf 0x7f2b87aeecb0 0xaa7241 0xd4cccc 0xd4d69d 0xd4f81e 0xc443c9 0xc504b6 0xa05661 0xa05df0 0xa08cff 0xa0980d 0xa0d3ee 0xa2295a 0xa2431b 0xa26269 0xd549f7 0xb9c972
/usr/bin/mongod-shard(_ZN5mongo15printStackTraceERSo+0x21) [0x11da801]
/usr/bin/mongod-shard() [0x11d9bde]
/usr/bin/mongod-shard() [0x11d9ccf]
/lib/x86_64-linux-gnu/libpthread.so.0(+0xfcb0) [0x7f2b87aeecb0]
/usr/bin/mongod-shard(_ZN5mongo18KeepMutationsStage4workEPm+0xc1) [0xaa7241]
/usr/bin/mongod-shard(_ZN5mongo15MultiPlanRunner12workAllPlansEPNS_7BSONObjEm+0x13c) [0xd4cccc]
/usr/bin/mongod-shard(_ZN5mongo15MultiPlanRunner12pickBestPlanEPmPNS_7BSONObjE+0xed) [0xd4d69d]
/usr/bin/mongod-shard(_ZN5mongo15MultiPlanRunner7getNextEPNS_7BSONObjEPNS_7DiskLocE+0x34e) [0xd4f81e]
/usr/bin/mongod-shard(_ZN5mongo6updateERKNS_13UpdateRequestEPNS_7OpDebugEPNS_12UpdateDriverEPNS_14CanonicalQueryE+0x9c9) [0xc443c9]
/usr/bin/mongod-shard(_ZN5mongo14UpdateExecutor7executeEv+0x66) [0xc504b6]
/usr/bin/mongod-shard() [0xa05661]
/usr/bin/mongod-shard(_ZN5mongo18WriteBatchExecutor10execUpdateERKNS_12BatchItemRefEPNS_7BSONObjEPPNS_16WriteErrorDetailE+0x80) [0xa05df0]
/usr/bin/mongod-shard(_ZN5mongo18WriteBatchExecutor11bulkExecuteERKNS_21BatchedCommandRequestEPSt6vectorIPNS_19BatchedUpsertDetailESaIS6_EEPS4_IPNS_16WriteErrorDetailESaISB_EE+0x1df) [0xa08cff]
/usr/bin/mongod-shard(_ZN5mongo18WriteBatchExecutor12executeBatchERKNS_21BatchedCommandRequestEPNS_22BatchedCommandResponseE+0x8cd) [0xa0980d]
/usr/bin/mongod-shard(_ZN5mongo8WriteCmd3runERKSsRNS_7BSONObjEiRSsRNS_14BSONObjBuilderEb+0x3de) [0xa0d3ee]
/usr/bin/mongod-shard(_ZN5mongo12_execCommandEPNS_7CommandERKSsRNS_7BSONObjEiRSsRNS_14BSONObjBuilderEb+0x3a) [0xa2295a]
/usr/bin/mongod-shard(_ZN5mongo7Command11execCommandEPS0_RNS_6ClientEiPKcRNS_7BSONObjERNS_14BSONObjBuilderEb+0xfeb) [0xa2431b]
/usr/bin/mongod-shard(_ZN5mongo12_runCommandsEPKcRNS_7BSONObjERNS_11_BufBuilderINS_16TrivialAllocatorEEERNS_14BSONObjBuilderEbi+0x6c9) [0xa26269]
/usr/bin/mongod-shard(ZN5mongo11newRunQueryERNS_7MessageERNS_12QueryMessageERNS_5CurOpES1+0x2307) [0xd549f7]
/usr/bin/mongod-shard() [0xb9c972]