1925 stack overflow from mac code

@@ -20,17 +20,22 @@
  */
 /*
  * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */
+/*
+ * Copyright 2011 Joyent, Inc.  All rights reserved.
+ */
 
 #include <sys/types.h>
 #include <sys/callb.h>
 #include <sys/sdt.h>
 #include <sys/strsubr.h>
 #include <sys/strsun.h>
 #include <sys/vlan.h>
+#include <sys/stack.h>
+#include <sys/archsystm.h>
 #include <inet/ipsec_impl.h>
 #include <inet/ip_impl.h>
 #include <inet/sadb.h>
 #include <inet/ipsecesp.h>
 #include <inet/ipsecah.h>

@@ -413,10 +418,32 @@
         cookie = (mac_tx_cookie_t)srs;                                  \
         *ret_mp = mp_chain;                                             \
 }
 
 /*
+ * MAC_RX_SRS_TOODEEP
+ *
+ * Macro called as part of receive-side processing to determine if handling
+ * can occur in situ (in the interrupt thread) or if it should be left to a
+ * worker thread.  Note that the constant used to make this determination is
+ * not entirely made-up, and is a result of some emprical validation. That
+ * said, the constant is left as a static variable to allow it to be
+ * dynamically tuned in the field if and as needed.
+ */
+static uintptr_t mac_rx_srs_stack_needed = 10240;
+static uint_t mac_rx_srs_stack_toodeep;
+
+#ifndef STACK_GROWTH_DOWN
+#error Downward stack growth assumed.
+#endif
+
+#define MAC_RX_SRS_TOODEEP() (STACK_BIAS + (uintptr_t)getfp() - \
+        (uintptr_t)curthread->t_stkbase < mac_rx_srs_stack_needed && \
+        ++mac_rx_srs_stack_toodeep)
+
+
+/*
  * Drop the rx packet and advance to the next one in the chain.
  */
 static void
 mac_rx_drop_pkt(mac_soft_ring_set_t *srs, mblk_t *mp)
 {

@@ -2417,15 +2444,16 @@
 
         MAC_RX_SRS_ENQUEUE_CHAIN(mac_srs, mp_chain, tail, count, sz);
 
         if (!(mac_srs->srs_state & SRS_PROC)) {
                 /*
-                 * If we are coming via loopback or if we are not
-                 * optimizing for latency, we should signal the
-                 * worker thread.
+                 * If we are coming via loopback, if we are not optimizing for
+                 * latency, or if our stack is running deep, we should signal
+                 * the worker thread.
                  */
-                if (loopback || !(mac_srs->srs_state & SRS_LATENCY_OPT)) {
+                if (loopback || !(mac_srs->srs_state & SRS_LATENCY_OPT) ||
+                    MAC_RX_SRS_TOODEEP()) {
                         /*
                          * For loopback, We need to let the worker take
                          * over as we don't want to continue in the same
                          * thread even if we can. This could lead to stack
                          * overflows and may also end up using