lock: Fix interactions between lock dependency checker and stack checker

The lock dependency checker does a few nasty things that can cause
re-entrancy deadlocks in conjunction with the stack checker or
in fact other debug tests.

A lot of it revolves around taking a new lock (dl_lock) as part
of the locking process.

This tries to fix it by making sure we do not hit the stack
checker while holding dl_lock.

We achieve that in part by directly using the low-level __try_lock
and manually unlocking on the dl_lock, and making some functions
"nomcount".

In addition, we mark the dl_lock as being in the console path to
avoid deadlocks with the UART driver.

We move the enabling of the deadlock checker to a separate config
option from DEBUG_LOCKS as well, in case we chose to disable it
by default later on.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Stewart Smith <stewart@linux.ibm.com>

2 files changed, 6 insertions, 0 deletions

diff --git a/include/config.h b/include/config.h
index cd8a0a65..6b36590c 100644
--- a/include/config.h
+++ b/include/config.h
@@ -39,6 +39,9 @@
 /* Enable lock debugging */
 #define DEBUG_LOCKS		1
 
+/* Enable lock dependency checker */
+#define DEADLOCK_CHECKER	1
+
 /* Enable malloc debugging */
 #define DEBUG_MALLOC		1
 
diff --git a/include/cpu.h b/include/cpu.h
index ae318572..2fe47982 100644
--- a/include/cpu.h
+++ b/include/cpu.h
@@ -174,6 +174,9 @@ extern struct cpu_thread *find_cpu_by_node(struct dt_node *cpu);
 extern struct cpu_thread *find_cpu_by_server(u32 server_no);
 extern struct cpu_thread *find_cpu_by_pir(u32 pir);
 
+/* Used for lock internals to avoid re-entrancy */
+extern struct __nomcount cpu_thread *find_cpu_by_pir_nomcount(u32 pir);
+
 extern struct dt_node *get_cpu_node(u32 pir);
 
 /* Iterator */