microblaze: Lockdep support

Microblaze needs to do lock_init very soon because MMU init calls lock functions.

Here is the explanation from Peter Zijlstra why we have to enable
__ARCH_WANTS_INTERRUPTS_ON_CTSW.

"So we schedule while holding rq->lock (for obvious reasons), but since
lockdep tracks held locks per tasks, we need to transfer the held state
from the prev to the next task. We do this by explicity calling
spin_release(&rq->lock) in context_switch() right before switch_to(),
and calling spin_acquire(&rq->lock) in
finish_task_switch()->finish_lock_switch().

Now, for some reason lockdep thinks that interrupts got enabled over the
context switch (git grep __ARCH_WANTS_INTERRUPTS_ON_CTSW arch/microblaze
doesn't seem to turn up anything).

Clearly trying to acquire the rq->lock with interrupts enabled is a bad
idea and lockdep warns you about this."

Signed-off-by: Michal Simek <monstr@monstr.eu>

3 files changed, 7 insertions, 0 deletions

diff --git a/arch/microblaze/Kconfig b/arch/microblaze/Kconfig
index 8e1c4f7d3e6e..5ba4dcd56cad 100644
--- a/arch/microblaze/Kconfig
+++ b/arch/microblaze/Kconfig
@@ -60,6 +60,9 @@ config GENERIC_CSUM
 config STACKTRACE_SUPPORT
         def_bool y
 
+config LOCKDEP_SUPPORT
+        def_bool y
+
 config PCI
         def_bool n
 
diff --git a/arch/microblaze/include/asm/system.h b/arch/microblaze/include/asm/system.h
index b1ed61590660..157970688b2a 100644
--- a/arch/microblaze/include/asm/system.h
+++ b/arch/microblaze/include/asm/system.h
@@ -16,6 +16,8 @@
 #include <asm-generic/cmpxchg.h>
 #include <asm-generic/cmpxchg-local.h>
 
+#define __ARCH_WANT_INTERRUPTS_ON_CTXSW
+
 struct task_struct;
 struct thread_info;
 
diff --git a/arch/microblaze/kernel/setup.c b/arch/microblaze/kernel/setup.c
index 367ad330148e..acd70fe30a71 100644
--- a/arch/microblaze/kernel/setup.c
+++ b/arch/microblaze/kernel/setup.c
@@ -131,6 +131,8 @@ void __init machine_early_init(const char *cmdline, unsigned int ram,
                 strlcpy(cmd_line, cmdline, COMMAND_LINE_SIZE);
 #endif
 
+        lockdep_init();
+
 /* initialize device tree for usage in early_printk */
         early_init_devtree((void *)_fdt_start);