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authorKrister Johansen <kjlx@templeofstupid.com>2017-06-08 13:12:38 -0700
committerDavid S. Miller <davem@davemloft.net>2017-06-09 12:27:28 -0400
commitf186ce61bb8235d80068c390dc2aad7ca427a4c2 (patch)
treec6fdbaf52c8a4cdea9edf928fa5b3add833c0f7f /net/core/dst.c
parentdefbcf2decc903a28d8398aa477b6881e711e3ea (diff)
Fix an intermittent pr_emerg warning about lo becoming free.
It looks like this: Message from syslogd@flamingo at Apr 26 00:45:00 ... kernel:unregister_netdevice: waiting for lo to become free. Usage count = 4 They seem to coincide with net namespace teardown. The message is emitted by netdev_wait_allrefs(). Forced a kdump in netdev_run_todo, but found that the refcount on the lo device was already 0 at the time we got to the panic. Used bcc to check the blocking in netdev_run_todo. The only places where we're off cpu there are in the rcu_barrier() and msleep() calls. That behavior is expected. The msleep time coincides with the amount of time we spend waiting for the refcount to reach zero; the rcu_barrier() wait times are not excessive. After looking through the list of callbacks that the netdevice notifiers invoke in this path, it appears that the dst_dev_event is the most interesting. The dst_ifdown path places a hold on the loopback_dev as part of releasing the dev associated with the original dst cache entry. Most of our notifier callbacks are straight-forward, but this one a) looks complex, and b) places a hold on the network interface in question. I constructed a new bcc script that watches various events in the liftime of a dst cache entry. Note that dst_ifdown will take a hold on the loopback device until the invalidated dst entry gets freed. [ __dst_free] on DST: ffff883ccabb7900 IF tap1008300eth0 invoked at 1282115677036183 __dst_free rcu_nocb_kthread kthread ret_from_fork Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/core/dst.c')
-rw-r--r--net/core/dst.c14
1 files changed, 14 insertions, 0 deletions
diff --git a/net/core/dst.c b/net/core/dst.c
index 6192f11beec9..13ba4a090c41 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -469,6 +469,20 @@ static int dst_dev_event(struct notifier_block *this, unsigned long event,
spin_lock_bh(&dst_garbage.lock);
dst = dst_garbage.list;
dst_garbage.list = NULL;
+ /* The code in dst_ifdown places a hold on the loopback device.
+ * If the gc entry processing is set to expire after a lengthy
+ * interval, this hold can cause netdev_wait_allrefs() to hang
+ * out and wait for a long time -- until the the loopback
+ * interface is released. If we're really unlucky, it'll emit
+ * pr_emerg messages to console too. Reset the interval here,
+ * so dst cleanups occur in a more timely fashion.
+ */
+ if (dst_garbage.timer_inc > DST_GC_INC) {
+ dst_garbage.timer_inc = DST_GC_INC;
+ dst_garbage.timer_expires = DST_GC_MIN;
+ mod_delayed_work(system_wq, &dst_gc_work,
+ dst_garbage.timer_expires);
+ }
spin_unlock_bh(&dst_garbage.lock);
if (last)