core/lock: Add deadlock detection

This adds simple deadlock detection. The detection looks for circular
dependencies in the lock requests. It will abort and display a stack trace
when a deadlock occurs.
The detection is enabled by DEBUG_LOCKS (enabled by default).
While the detection may have a slight performance overhead, as there are
not a huge number of locks in skiboot this overhead isn't significant.

Signed-off-by: Matt Brown <matthew.brown.dev@gmail.com>
[stewart: fix build with DEBUG_LOCKS off]
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/core/cpu.c b/core/cpu.c
index 7a9dbe5..4914d30 100644
--- a/core/cpu.c
+++ b/core/cpu.c
@@ -1082,6 +1082,9 @@ void init_all_cpus(void)
 		t->node = cpu;
 		t->chip_id = chip_id;
 		t->icp_regs = NULL; /* Will be set later */
+#ifdef DEBUG_LOCKS
+		t->requested_lock = NULL;
+#endif
 		t->core_hmi_state = 0;
 		t->core_hmi_state_ptr = &t->core_hmi_state;
 		t->thread_mask = 1;