[uml-devel] [PATCH 4/5] UML: Avoid lockdep issues during initialization

[Paul Menage <menage@google.com>]

UML: Avoid lockdep issues during initialization

UML calls atomic_notifier_chain_register() very early during
initialization. When lockdep is in use, the spinlock operations thus
invoked make use of current_thread_info(), which isn't valid in UML
until start_kernel_proc() is reached (running on the init_thread_union
stack rather than the default stack at the top of the address space).

This patch moves the call to the beginning of start_kernel_proc(), and
additionally disables lock debugging for the duration of the call,
since lockdep_init() doesn't occur until start_kernel() is called.

Signed-off-by: Paul Menage <menage@google.com>

---

 arch/um/kernel/skas/process.c |   26 ++++++++++++++++++++++++++
 arch/um/kernel/um_arch.c      |   20 --------------------
 2 files changed, 26 insertions(+), 20 deletions(-)

diff --git a/arch/um/kernel/skas/process.c b/arch/um/kernel/skas/process.c
index 4a21c5c..2b62a72 100644
--- a/arch/um/kernel/skas/process.c
+++ b/arch/um/kernel/skas/process.c
@@ -5,7 +5,9 @@
 
 #include "linux/init.h"
 #include "linux/sched.h"
+#include "linux/debug_locks.h"
 #include "as-layout.h"
+#include "shared/kern_util.h"
 #include "kern.h"
 #include "os.h"
 #include "skas.h"
@@ -31,10 +33,34 @@ int new_mm(unsigned long stack)
 
 extern void start_kernel(void);
 
+static int panic_exit(struct notifier_block *self, unsigned long unused1,
+		      void *unused2)
+{
+	bust_spinlocks(1);
+	show_regs(&(current->thread.regs));
+	bust_spinlocks(0);
+	uml_exitcode = 1;
+	os_dump_core();
+	return 0;
+}
+
+static struct notifier_block panic_exit_notifier = {
+	.notifier_call 		= panic_exit,
+	.next 			= NULL,
+	.priority 		= 0
+};
+
 static int __init start_kernel_proc(void *unused)
 {
 	int pid;
 
+	/* lockdep hasn't yet been initialized, but this call takes
+	 * spinlocks. Temporarily disable lock debugging */
+	int saved_debug_locks = debug_locks;
+	debug_locks = 0;
+	atomic_notifier_chain_register(&panic_notifier_list,
+				       &panic_exit_notifier);
+	debug_locks = saved_debug_locks;
 	local_irq_disable();
 	pid = os_getpid();
 
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 8d84250..364c589 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -223,23 +223,6 @@ static void __init uml_postsetup(void)
 	return;
 }
 
-static int panic_exit(struct notifier_block *self, unsigned long unused1,
-		      void *unused2)
-{
-	bust_spinlocks(1);
-	show_regs(&(current->thread.regs));
-	bust_spinlocks(0);
-	uml_exitcode = 1;
-	os_dump_core();
-	return 0;
-}
-
-static struct notifier_block panic_exit_notifier = {
-	.notifier_call 		= panic_exit,
-	.next 			= NULL,
-	.priority 		= 0
-};
-
 /* Set during early boot */
 unsigned long task_size;
 EXPORT_SYMBOL(task_size);
@@ -360,9 +343,6 @@ int __init linux_main(int argc, char **argv)
 		printf("Kernel virtual memory size shrunk to %lu bytes\n",
 		       virtmem_size);
 
-	atomic_notifier_chain_register(&panic_notifier_list,
-				       &panic_exit_notifier);
-
 	uml_postsetup();
 
 	stack_protections((unsigned long) &init_thread_info);


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