USB: Acquire the device manager lock before Explore.

We must do this to prevent lock order inversion: when busses are
initialized, they are started by the (locked) device manager, and
then acquire the explore lock. We must do the same in Explore itself,
for when called by the explore thread, we would otherwise first acquire
the explore lock, then (when publishing new nodes) acquire the device lock.

Should fix #18421 and #18393.

headers/private/kernel/kdevice_manager.h

@@ -7,6 +7,7 @@
 
 
 #include <device_manager.h>
+#include <lock.h>
 
 struct kernel_args;
 
@@ -21,6 +22,8 @@ status_t device_manager_probe(const char *path, uint32 updateCycle);
 status_t device_manager_init(struct kernel_args *args);
 status_t device_manager_init_post_modules(struct kernel_args *args);
 
+recursive_lock* device_manager_get_lock();
+
 #ifdef __cplusplus
 }
 #endif

src/add-ons/kernel/bus_managers/usb/Stack.cpp

@@ -11,10 +11,13 @@
 #include <module.h>
 #include <unistd.h>
 #include <util/kernel_cpp.h>
+#include <util/AutoLock.h>
+
 #include "usb_private.h"
 #include "PhysicalMemoryAllocator.h"
 
 #include <fs/devfs.h>
+#include <kdevice_manager.h>
 
 
 Stack::Stack()
@@ -214,6 +217,9 @@ Stack::ExploreThread(void *data)
 void
 Stack::Explore()
 {
+	// Acquire the device manager lock before the explore lock, to prevent lock-order inversion.
+	RecursiveLocker dmLocker(device_manager_get_lock());
+
 	if (mutex_lock(&fExploreLock) != B_OK)
 		return;
 

src/system/kernel/device_manager/device_manager.cpp

@@ -2489,3 +2489,10 @@ device_manager_init_post_modules(struct kernel_args* args)
 	RecursiveLocker _(sLock);
 	return sRootNode->Reprobe();
 }
+
+
+recursive_lock*
+device_manager_get_lock()
+{
+	return &sLock;
+}