https://bugs.gentoo.org/694614
https://www.virtualbox.org/ticket/18911#comment:5

--- a/HostDrivers/VBoxNetFlt/linux/VBoxNetFlt-linux.c
+++ b/HostDrivers/VBoxNetFlt/linux/VBoxNetFlt-linux.c
@@ -2123,7 +2123,9 @@ static int vboxNetFltLinuxEnumeratorCallback(struct notifier_block *self, unsign
 #endif
     if (in_dev != NULL)
     {
-        for_ifa(in_dev) {
+        struct in_ifaddr *ifa;
+
+        for (ifa = in_dev->ifa_list; ifa; ifa = ifa->ifa_next) {
             if (VBOX_IPV4_IS_LOOPBACK(ifa->ifa_address))
                 return NOTIFY_OK;
 
@@ -2137,7 +2139,7 @@ static int vboxNetFltLinuxEnumeratorCallback(struct notifier_block *self, unsign
 
             pThis->pSwitchPort->pfnNotifyHostAddress(pThis->pSwitchPort,
                 /* :fAdded */ true, kIntNetAddrType_IPv4, &ifa->ifa_address);
-        } endfor_ifa(in_dev);
+        }
     }
 
     /*
--- a/Runtime/r0drv/linux/mp-r0drv-linux.c
+++ b/Runtime/r0drv/linux/mp-r0drv-linux.c
@@ -283,12 +283,15 @@ RTDECL(int) RTMpOnAll(PFNRTMPWORKER pfnWorker, void *pvUser1, void *pvUser2)
     if (RTCpuSetCount(&OnlineSet) > 1)
     {
         /* Fire the function on all other CPUs without waiting for completion. */
-# if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 27)
+# if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 3, 0)
+        smp_call_function(rtmpLinuxAllWrapper, &Args, 0 /* wait */);
+# elif LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 27)
         int rc = smp_call_function(rtmpLinuxAllWrapper, &Args, 0 /* wait */);
+        Assert(!rc); NOREF(rc);
 # else
         int rc = smp_call_function(rtmpLinuxAllWrapper, &Args, 0 /* retry */, 0 /* wait */);
-# endif
         Assert(!rc); NOREF(rc);
+# endif
     }
 #endif
 
@@ -326,7 +329,6 @@ RTDECL(int) RTMpOnOthers(PFNRTMPWORKER pfnWorker, void *pvUser1, void *pvUser2)
 {
 #ifdef CONFIG_SMP
     IPRT_LINUX_SAVE_EFL_AC();
-    int rc;
     RTMPARGS Args;
 
     RTTHREADPREEMPTSTATE PreemptState = RTTHREADPREEMPTSTATE_INITIALIZER;
@@ -337,14 +339,17 @@ RTDECL(int) RTMpOnOthers(PFNRTMPWORKER pfnWorker, void *pvUser1, void *pvUser2)
     Args.cHits = 0;
 
     RTThreadPreemptDisable(&PreemptState);
-# if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 27)
-    rc = smp_call_function(rtmpLinuxWrapper, &Args, 1 /* wait */);
+# if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 3, 0)
+    smp_call_function(rtmpLinuxWrapper, &Args, 1 /* wait */);
+# elif LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 27)
+    int rc = smp_call_function(rtmpLinuxWrapper, &Args, 1 /* wait */);
+    Assert(rc == 0); NOREF(rc);
 # else /* older kernels */
-    rc = smp_call_function(rtmpLinuxWrapper, &Args, 0 /* retry */, 1 /* wait */);
+    int rc = smp_call_function(rtmpLinuxWrapper, &Args, 0 /* retry */, 1 /* wait */);
+    Assert(rc == 0); NOREF(rc);
 # endif /* older kernels */
     RTThreadPreemptRestore(&PreemptState);
 
-    Assert(rc == 0); NOREF(rc);
     IPRT_LINUX_RESTORE_EFL_AC();
 #else
     RT_NOREF(pfnWorker, pvUser1, pvUser2);