libmagick hangs when called from RMagick with Passenger 3

ruby processes using libmagick via the RMagick gem hang when running under Passenger 3.0.11. The requests never return.

Installing debug libraries and looking at one of the stuck processes with gdb gives this:

#0 futex_wait (val=0, addr=0x3858984)
    at ../../../src/libgomp/config/linux/x86/futex.h:44
#1 do_wait (val=0, addr=0x3858984) at ../../../src/libgomp/config/linux/wait.h:58
#2 gomp_team_barrier_wait_end (bar=0x3858980, state=0)
    at ../../../src/libgomp/config/linux/bar.c:109
#3 0x00007f876709b6ce in gomp_team_end () at ../../../src/libgomp/team.c:464
#4 0x00007f876840a919 in SetImageBackgroundColor (image=0x1d27600)
    at magick/image.c:2837
#5 SetImageBackgroundColor (image=0x1d27600) at magick/image.c:2792
#6 0x00007f876879749e in Image_initialize ()
   from /usr/lib/ruby/gems/1.8/gems/rmagick-2.13.1/lib/RMagick2.so

The problem does not occur when using the Ubuntu Passenger package, only with more recent versions of Passenger.

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: libmagickcore3 8:6.6.0.4-3ubuntu1
ProcVersionSignature: Ubuntu 3.0.0-12.20-generic 3.0.4
Uname: Linux 3.0.0-12-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 1.23-0ubuntu4
Architecture: amd64
Date: Mon Feb 20 21:38:38 2012
ProcEnviron:
 LC_CTYPE=en_US.UTF-8
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/usr/bin/zsh
SourcePackage: imagemagick
UpgradeStatus: Upgraded to oneiric on 2011-10-15 (128 days ago)