ipv6: prevent fib6_run_gc() contention

On a high-traffic router with many processors and many IPv6 dst
entries, soft lockup in fib6_run_gc() can occur when number of
entries reaches gc_thresh.

This happens because fib6_run_gc() uses fib6_gc_lock to allow
only one thread to run the garbage collector but ip6_dst_gc()
doesn't update net->ipv6.ip6_rt_last_gc until fib6_run_gc()
returns. On a system with many entries, this can take some time
so that in the meantime, other threads pass the tests in
ip6_dst_gc() (ip6_rt_last_gc is still not updated) and wait for
the lock. They then have to run the garbage collector one after
another which blocks them for quite long.

Resolve this by replacing special value ~0UL of expire parameter
to fib6_run_gc() by explicit "force" parameter to choose between
spin_lock_bh() and spin_trylock_bh() and call fib6_run_gc() with
force=false if gc_thresh is reached but not max_size.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 2a601e7da1bfc8b97490075531975dcdfebc8370..48ec25a7fcb60a09a2c323c70221a31853a82261 100644 (file)
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -300,7 +300,7 @@ extern void                 inet6_rt_notify(int event, struct rt6_info *rt,
                                                struct nl_info *info);
 
 extern void                    fib6_run_gc(unsigned long expires,
-                                           struct net *net);
+                                           struct net *net, bool force);
 
 extern void                    fib6_gc_cleanup(void);
 

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 5fc9c7a68d8d102aef37b7b13ab1dd772553a9cb..d872553ca933078061459dbc9fcc61d0764cf689 100644 (file)
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -1632,19 +1632,16 @@ static int fib6_age(struct rt6_info *rt, void *arg)
 
 static DEFINE_SPINLOCK(fib6_gc_lock);
 
-void fib6_run_gc(unsigned long expires, struct net *net)
+void fib6_run_gc(unsigned long expires, struct net *net, bool force)
 {
-       if (expires != ~0UL) {
+       if (force) {
                spin_lock_bh(&fib6_gc_lock);
-               gc_args.timeout = expires ? (int)expires :
-                       net->ipv6.sysctl.ip6_rt_gc_interval;
-       } else {
-               if (!spin_trylock_bh(&fib6_gc_lock)) {
-                       mod_timer(&net->ipv6.ip6_fib_timer, jiffies + HZ);
-                       return;
-               }
-               gc_args.timeout = net->ipv6.sysctl.ip6_rt_gc_interval;
+       } else if (!spin_trylock_bh(&fib6_gc_lock)) {
+               mod_timer(&net->ipv6.ip6_fib_timer, jiffies + HZ);
+               return;
        }
+       gc_args.timeout = expires ? (int)expires :
+                         net->ipv6.sysctl.ip6_rt_gc_interval;
 
        gc_args.more = icmp6_dst_gc();
 
@@ -1661,7 +1658,7 @@ void fib6_run_gc(unsigned long expires, struct net *net)
 
 static void fib6_gc_timer_cb(unsigned long arg)
 {
-       fib6_run_gc(0, (struct net *)arg);
+       fib6_run_gc(0, (struct net *)arg, true);
 }
 
 static int __net_init fib6_net_init(struct net *net)

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 24c03396e0083b751d2a924b69b2dc731f1b957f..79aa9652ed86d9cac754366c075800fbbe4aca1b 100644 (file)
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1576,7 +1576,7 @@ static int ndisc_netdev_event(struct notifier_block *this, unsigned long event,
        switch (event) {
        case NETDEV_CHANGEADDR:
                neigh_changeaddr(&nd_tbl, dev);
-               fib6_run_gc(~0UL, net);
+               fib6_run_gc(0, net, false);
                idev = in6_dev_get(dev);
                if (!idev)
                        break;
@@ -1586,7 +1586,7 @@ static int ndisc_netdev_event(struct notifier_block *this, unsigned long event,
                break;
        case NETDEV_DOWN:
                neigh_ifdown(&nd_tbl, dev);
-               fib6_run_gc(~0UL, net);
+               fib6_run_gc(0, net, false);
                break;
        case NETDEV_NOTIFY_PEERS:
                ndisc_send_unsol_na(dev);

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index a8c891aa24645e9a45d2f8e47712b0698a29b216..824c424f96485a2a8fca78f3b0110c501cd17d44 100644 (file)
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1326,7 +1326,7 @@ static int ip6_dst_gc(struct dst_ops *ops)
                goto out;
 
        net->ipv6.ip6_rt_gc_expire++;
-       fib6_run_gc(net->ipv6.ip6_rt_gc_expire, net);
+       fib6_run_gc(net->ipv6.ip6_rt_gc_expire, net, entries > rt_max_size);
        net->ipv6.ip6_rt_last_gc = now;
        entries = dst_entries_get_slow(ops);
        if (entries < ops->gc_thresh)
@@ -2827,7 +2827,7 @@ int ipv6_sysctl_rtcache_flush(struct ctl_table *ctl, int write,
        net = (struct net *)ctl->extra1;
        delay = net->ipv6.sysctl.flush_delay;
        proc_dointvec(ctl, write, buffer, lenp, ppos);
-       fib6_run_gc(delay <= 0 ? ~0UL : (unsigned long)delay, net);
+       fib6_run_gc(delay <= 0 ? 0 : (unsigned long)delay, net, delay > 0);
        return 0;
 }