Don't bother calling the module event handlers from module_shutdown()

in the shutdown_final state if the RB_NOSYNC flag is set.

The specific motivation in this case is that a system panic in an
interrupt context results in a call to module_shutdown(), which
calls g_modevent(), which calls g_malloc(..., M_WAITOK), which
results in a second panic.   While g_modevent() could be fixed to
not call malloc() for MOD_SHUTDOWN events (which it doesn't handle
in any case), it is probably also a good idea to entirely skip the
execution of the module shutdown handlers after a panic.

This may be a MFC candidate for RELENG_5.

1 files changed, 3 insertions, 0 deletions

diff --git a/sys/kern/kern_module.c b/sys/kern/kern_module.c
index 9dfe3ba..cecb2e1 100644
--- a/sys/kern/kern_module.c
+++ b/sys/kern/kern_module.c
@@ -37,6 +37,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/proc.h>
 #include <sys/lock.h>
 #include <sys/mutex.h>
+#include <sys/reboot.h>
 #include <sys/sx.h>
 #include <sys/module.h>
 #include <sys/linker.h>
@@ -94,6 +95,8 @@ module_shutdown(void *arg1, int arg2)
 {
 	module_t mod;
 
+	if (arg2 & RB_NOSYNC)
+		return;
 	MOD_SLOCK;
 	TAILQ_FOREACH(mod, &modules, link)
 		MOD_EVENT(mod, MOD_SHUTDOWN);