On my 2.6.18 kernel guile (latest snapshot from git, branch-release-1.8 head) in some situations (unfortunately I can't made a testcase) stops forever. Guile with 2.6.27 kernel works well.
Strace: futex(0xc571890, FUTEX_WAIT, 2, NULL...
Backtrace: -- #0 0x00002b4ba31b4004 in __lll_lock_wait () from /lib64/libpthread.so.0 #1 0x00002b4ba31af944 in _L_lock_55 () from /lib64/libpthread.so.0
#2 0x00002b4ba31af341 in pthread_mutex_lock () from /lib64/libpthread.so.0 #3 0x00002b4ba22f87dc in scm_i_thread_put_to_sleep () from /usr/lib64/libguile.so.17 #4 0x00002b4ba22abfd9 in scm_i_gc () from /usr/lib64/libguile.so.17
#5 0x00002b4ba22ac338 in scm_gc_for_newcell () from /usr/lib64/libguile.so.17 #6 0x00002b4ba22cc86f in scm_cons () from /usr/lib64/libguile.so.17 --