https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92836
--- Comment #1 from Andrew Benson <abensonca at gmail dot com> ---
Running with -fsanitize=thread (suggested by Tobias) gives:
==================
WARNING: ThreadSanitizer: lock-order-inversion (potential deadlock) (pid=9982)
Cycle in lock order graph: M26 (0x7f02bb31c340) => M84 (0x7b58002efee0) =>
M26
Mutex M84 acquired here while holding mutex M26 in thread T63:
#0 pthread_mutex_lock ../../../../gcc-trunk/libsanitizer/sanitizer_common/
sanitizer_common_interceptors.inc:4148 (libtsan.so.0+0x5095a)
#1 __gthread_mutex_lock ../libgcc/gthr-default.h:749 (libgfortran.so.
5+0x1e25c9)
#2 insert_unit ../../../gcc-trunk/libgfortran/io/unit.c:244
(libgfortran.so.5+0x1e25c9)
#3 gomp_thread_start ../../../gcc-trunk/libgomp/team.c:123 (libgomp.so.
1+0x198a5)
Mutex M26 previously acquired by the same thread here:
#0 pthread_mutex_lock ../../../../gcc-trunk/libsanitizer/sanitizer_common/
sanitizer_common_interceptors.inc:4148 (libtsan.so.0+0x5095a)
#1 __gthread_mutex_lock ../libgcc/gthr-default.h:749 (libgfortran.so.
5+0x1e265c)
#2 get_gfc_unit ../../../gcc-trunk/libgfortran/io/unit.c:332
(libgfortran.so.5+0x1e265c)
#3 gomp_thread_start ../../../gcc-trunk/libgomp/team.c:123 (libgomp.so.
1+0x198a5)
Mutex M26 acquired here while holding mutex M84 in thread T63:
#0 pthread_mutex_lock ../../../../gcc-trunk/libsanitizer/sanitizer_common/
sanitizer_common_interceptors.inc:4148 (libtsan.so.0+0x5095a)
#1 __gthread_mutex_lock ../libgcc/gthr-default.h:749 (libgfortran.so.
5+0x1e336b)
#2 close_unit_1 ../../../gcc-trunk/libgfortran/io/unit.c:735
(libgfortran.so.5+0x1e336b)
#3 gomp_thread_start ../../../gcc-trunk/libgomp/team.c:123 (libgomp.so.
1+0x198a5)
Mutex M84 previously acquired by the same thread here:
#0 pthread_mutex_trylock ../../../../gcc-trunk/libsanitizer/tsan/
tsan_interceptors_posix.cpp:1246 (libtsan.so.0+0x4340a)
#1 __gthread_mutex_trylock ../libgcc/gthr-default.h:758 (libgfortran.so.
5+0x1e26f1)
#2 get_gfc_unit ../../../gcc-trunk/libgfortran/io/unit.c:380
(libgfortran.so.5+0x1e26f1)
#3 gomp_thread_start ../../../gcc-trunk/libgomp/team.c:123 (libgomp.so.
1+0x198a5)
Thread T63 (tid=10047, running) created by main thread at:
#0 pthread_create ../../../../gcc-trunk/libsanitizer/tsan/
tsan_interceptors_posix.cpp:962 (libtsan.so.0+0x5bb22)
#1 gomp_team_start ../../../gcc-trunk/libgomp/team.c:839 (libgomp.so.
1+0x19eba)
#2 main <null> (a.out+0x400ef9)
SUMMARY: ThreadSanitizer: lock-order-inversion (potential deadlock) ../libgcc/
gthr-default.h:749 in __gthread_mutex_lock
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