"stuck spinlock"

Greetings,

Immediately after an upgrade from 9.3.1 to 9.3.2, we have a client getting frequent (hourly) errors of the form:

/var/lib/postgresql/9.3/main/pg_log/postgresql-2013-12-12_211710.csv:2013-12-12 21:40:10.328
UTC,"n","n",32376,"10.2.1.142:52451",52aa24eb.7e78,5,"SELECT",2013-12-1221:04:43 UTC,9/7178,0,PANIC,XX000,"stuck
spinlock(0x7f7df94672f4) detected at
/tmp/buildd/postgresql-9.3-9.3.2/build/../src/backend/storage/buffer/bufmgr.c:1099",,,,,,"<redacted>"

uname -a: Linux postgresql3-master 3.8.0-33-generic #48~precise1-Ubuntu SMP Thu Oct 24 16:28:06 UTC 2013 x86_64 x86_64
x86_64GNU/Linux. 

Generally, there's no core file (which is currently enable), as the postmaster just normally exits the backend.

Diagnosis suggestions?
--
-- Christophe Pettus  xof@thebuild.com