FreeBSD/Linux Kernel Cross Reference
sys/net/netisr.c

     /*-
      * Copyright (c) 2001,2002,2003 Jonathan Lemon <jlemon@FreeBSD.org>
      * Copyright (c) 1997, Stefan Esser <se@freebsd.org>
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     * $FreeBSD$
     */
    
    #include "opt_net.h"
    
    #include <sys/param.h>
    #include <sys/bus.h>
    #include <sys/rtprio.h>
    #include <sys/systm.h>
    #include <sys/interrupt.h>
    #include <sys/kernel.h>
    #include <sys/kthread.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/proc.h>
    #include <sys/random.h>
    #include <sys/resourcevar.h>
    #include <sys/sysctl.h>
    #include <sys/unistd.h>
    #include <machine/atomic.h>
    #include <machine/cpu.h>
    #include <machine/stdarg.h>
    
    #include <sys/mbuf.h>
    #include <sys/socket.h>
    
    #include <net/if.h>
    #include <net/if_types.h>
    #include <net/if_var.h>
    #include <net/netisr.h>
    
    /* 
     * debug_mpsafenet controls network subsystem-wide use of the Giant lock,
     * from system calls down to interrupt handlers.  It can be changed only via
     * a tunable at boot, not at run-time, due to the complexity of unwinding.
     * The compiled default is set via a kernel option; right now, the default
     * unless otherwise specified is to run the network stack without Giant.
     */
    #ifdef NET_WITH_GIANT
    int     debug_mpsafenet = 0;
    #else
    int     debug_mpsafenet = 1;
    #endif
    int     debug_mpsafenet_toolatetotwiddle = 0;
    
    TUNABLE_INT("debug.mpsafenet", &debug_mpsafenet);
    SYSCTL_INT(_debug, OID_AUTO, mpsafenet, CTLFLAG_RD, &debug_mpsafenet, 0,
        "Enable/disable MPSAFE network support");
    
    volatile unsigned int   netisr; /* scheduling bits for network */
    
    struct netisr {
            netisr_t        *ni_handler;
            struct ifqueue  *ni_queue;
            int             ni_flags;
    } netisrs[32];
    
    static void *net_ih;
    
    /*
     * Not all network code is currently capable of running MPSAFE; however,
     * most of it is.  Since those sections that are not are generally optional
     * components not shipped with default kernels, we provide a basic way to
     * determine whether MPSAFE operation is permitted: based on a default of
     * yes, we permit non-MPSAFE components to use a registration call to
     * identify that they require Giant.  If the system is early in the boot
     * process still, then we change the debug_mpsafenet setting to choose a
     * non-MPSAFE execution mode (degraded).  If it's too late for that (since
     * the setting cannot be changed at run time), we generate a console warning
     * that the configuration may be unsafe.
     */
    static int mpsafe_warn_count;
    
   /*
    * Function call implementing registration of a non-MPSAFE network component.
    */
   void
   net_warn_not_mpsafe(const char *component)
   {
   
           /*
            * If we're running with Giant over the network stack, there is no
            * problem.
            */
           if (!debug_mpsafenet)
                   return;
   
           /*
            * If it's not too late to change the MPSAFE setting for the network
            * stack, do so now.  This effectively suppresses warnings by
            * components registering later.
            */
           if (!debug_mpsafenet_toolatetotwiddle) {
                   debug_mpsafenet = 0;
                   printf("WARNING: debug.mpsafenet forced to 0 as %s requires "
                       "Giant\n", component);
                   return;
           }
   
           /*
            * We must run without Giant, so generate a console warning with some
            * information with what to do about it.  The system may be operating
            * unsafely, however.
            */
           printf("WARNING: Network stack Giant-free, but %s requires Giant.\n",
               component);
           if (mpsafe_warn_count == 0)
                   printf("    Consider adding 'options NET_WITH_GIANT' or "
                       "setting debug.mpsafenet=0\n");
           mpsafe_warn_count++;
   }
   
   /*
    * This sysinit is run after any pre-loaded or compiled-in components have
    * announced that they require Giant, but before any modules loaded at
    * run-time.
    */
   static void
   net_mpsafe_toolate(void *arg)
   {
   
           debug_mpsafenet_toolatetotwiddle = 1;
   
           if (!debug_mpsafenet)
                   printf("WARNING: MPSAFE network stack disabled, expect "
                       "reduced performance.\n");
   }
   
   SYSINIT(net_mpsafe_toolate, SI_SUB_SETTINGS, SI_ORDER_ANY, net_mpsafe_toolate,
       NULL);
   
   void
   legacy_setsoftnet(void)
   {
           swi_sched(net_ih, 0);
   }
   
   void
   netisr_register(int num, netisr_t *handler, struct ifqueue *inq, int flags)
   {
           
           KASSERT(!(num < 0 || num >= (sizeof(netisrs)/sizeof(*netisrs))),
               ("bad isr %d", num));
           netisrs[num].ni_handler = handler;
           netisrs[num].ni_queue = inq;
           if ((flags & NETISR_MPSAFE) && !debug_mpsafenet)
                   flags &= ~NETISR_MPSAFE;
           netisrs[num].ni_flags = flags;
   }
   
   void
   netisr_unregister(int num)
   {
           struct netisr *ni;
           
           KASSERT(!(num < 0 || num >= (sizeof(netisrs)/sizeof(*netisrs))),
               ("bad isr %d", num));
           ni = &netisrs[num];
           ni->ni_handler = NULL;
           if (ni->ni_queue != NULL)
                   IF_DRAIN(ni->ni_queue);
           ni->ni_queue = NULL;
   }
   
   struct isrstat {
           int     isrs_count;                     /* dispatch count */
           int     isrs_directed;                  /* ...directly dispatched */
           int     isrs_deferred;                  /* ...queued instead */
           int     isrs_queued;                    /* intentionally queueued */
           int     isrs_drop;                      /* dropped 'cuz no handler */
           int     isrs_swi_count;                 /* swi_net handlers called */
   };
   static struct isrstat isrstat;
   
   SYSCTL_NODE(_net, OID_AUTO, isr, CTLFLAG_RW, 0, "netisr counters");
   
   static int      netisr_enable = 0;
   SYSCTL_INT(_net_isr, OID_AUTO, enable, CTLFLAG_RW, 
       &netisr_enable, 0, "enable direct dispatch");
   TUNABLE_INT("net.isr.enable", &netisr_enable);
   
   SYSCTL_INT(_net_isr, OID_AUTO, count, CTLFLAG_RD,
       &isrstat.isrs_count, 0, "");
   SYSCTL_INT(_net_isr, OID_AUTO, directed, CTLFLAG_RD, 
       &isrstat.isrs_directed, 0, "");
   SYSCTL_INT(_net_isr, OID_AUTO, deferred, CTLFLAG_RD, 
       &isrstat.isrs_deferred, 0, "");
   SYSCTL_INT(_net_isr, OID_AUTO, queued, CTLFLAG_RD, 
       &isrstat.isrs_queued, 0, "");
   SYSCTL_INT(_net_isr, OID_AUTO, drop, CTLFLAG_RD, 
       &isrstat.isrs_drop, 0, "");
   SYSCTL_INT(_net_isr, OID_AUTO, swi_count, CTLFLAG_RD, 
       &isrstat.isrs_swi_count, 0, "");
   
   /*
    * Process all packets currently present in a netisr queue.  Used to
    * drain an existing set of packets waiting for processing when we
    * begin direct dispatch, to avoid processing packets out of order.
    */
   static void
   netisr_processqueue(struct netisr *ni)
   {
           struct mbuf *m;
   
           for (;;) {
                   IF_DEQUEUE(ni->ni_queue, m);
                   if (m == NULL)
                           break;
                   ni->ni_handler(m);
           }
   }
   
   /*
    * Call the netisr directly instead of queueing the packet, if possible.
    */
   void
   netisr_dispatch(int num, struct mbuf *m)
   {
           struct netisr *ni;
           
           isrstat.isrs_count++;           /* XXX redundant */
           KASSERT(!(num < 0 || num >= (sizeof(netisrs)/sizeof(*netisrs))),
               ("bad isr %d", num));
           ni = &netisrs[num];
           if (ni->ni_queue == NULL) {
                   isrstat.isrs_drop++;
                   m_freem(m);
                   return;
           }
           /*
            * Do direct dispatch only for MPSAFE netisrs (and
            * only when enabled).  Note that when a netisr is
            * marked MPSAFE we permit multiple concurrent instances
            * to run.  We guarantee only the order in which
            * packets are processed for each "dispatch point" in
            * the system (i.e. call to netisr_dispatch or
            * netisr_queue).  This insures ordering of packets
            * from an interface but does not guarantee ordering
            * between multiple places in the system (e.g. IP
            * dispatched from interfaces vs. IP queued from IPSec).
            */
           if (netisr_enable && (ni->ni_flags & NETISR_MPSAFE)) {
                   isrstat.isrs_directed++;
                   /*
                    * NB: We used to drain the queue before handling
                    * the packet but now do not.  Doing so here will
                    * not preserve ordering so instead we fallback to
                    * guaranteeing order only from dispatch points
                    * in the system (see above).
                    */
                   ni->ni_handler(m);
           } else {
                   isrstat.isrs_deferred++;
                   if (IF_HANDOFF(ni->ni_queue, m, NULL))
                           schednetisr(num);
           }
   }
   
   /*
    * Same as above, but always queue.
    * This is either used in places where we are not confident that
    * direct dispatch is possible, or where queueing is required.
    * It returns (0) on success and ERRNO on failure.  On failure the
    * mbuf has been free'd.
    */
   int
   netisr_queue(int num, struct mbuf *m)
   {
           struct netisr *ni;
           
           KASSERT(!(num < 0 || num >= (sizeof(netisrs)/sizeof(*netisrs))),
               ("bad isr %d", num));
           ni = &netisrs[num];
           if (ni->ni_queue == NULL) {
                   isrstat.isrs_drop++;
                   m_freem(m);
                   return (ENXIO);
           }
           isrstat.isrs_queued++;
           if (!IF_HANDOFF(ni->ni_queue, m, NULL))
                   return (ENOBUFS);       /* IF_HANDOFF has free'd the mbuf */
           schednetisr(num);
           return (0);
   }
   
   static void
   swi_net(void *dummy)
   {
           struct netisr *ni;
           u_int bits;
           int i;
   #ifdef DEVICE_POLLING
           const int polling = 1;
   #else
           const int polling = 0;
   #endif
   
           do {
                   bits = atomic_readandclear_int(&netisr);
                   if (bits == 0)
                           break;
                   while ((i = ffs(bits)) != 0) {
                           isrstat.isrs_swi_count++;
                           i--;
                           bits &= ~(1 << i);
                           ni = &netisrs[i];
                           if (ni->ni_handler == NULL) {
                                   printf("swi_net: unregistered isr %d.\n", i);
                                   continue;
                           }
                           if ((ni->ni_flags & NETISR_MPSAFE) == 0) {
                                   mtx_lock(&Giant);
                                   if (ni->ni_queue == NULL)
                                           ni->ni_handler(NULL);
                                   else
                                           netisr_processqueue(ni);
                                   mtx_unlock(&Giant);
                           } else {
                                   if (ni->ni_queue == NULL)
                                           ni->ni_handler(NULL);
                                   else
                                           netisr_processqueue(ni);
                           }
                   }
           } while (polling);
   }
   
   static void
   start_netisr(void *dummy)
   {
   
           if (swi_add(NULL, "net", swi_net, NULL, SWI_NET, INTR_MPSAFE, &net_ih))
                   panic("start_netisr");
   }
   SYSINIT(start_netisr, SI_SUB_SOFTINTR, SI_ORDER_FIRST, start_netisr, NULL)

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