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| author | Krister Johansen <kjlx@templeofstupid.com> | 2017-06-08 23:12:38 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-07-05 15:40:14 +0300 |
| commit | c6d4ff85722b25877af48b311eda944dcc8c6feb (patch) | |
| tree | f7af9baad47a0d4b233712686fff490944193e00 /net/core | |
| parent | bb84290cd2967a5774a97fa44381713e20a7924c (diff) | |
| download | linux-c6d4ff85722b25877af48b311eda944dcc8c6feb.tar.xz | |
Fix an intermittent pr_emerg warning about lo becoming free.
[ Upstream commit f186ce61bb8235d80068c390dc2aad7ca427a4c2 ]
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'net/core')
| -rw-r--r-- | net/core/dst.c | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/net/core/dst.c b/net/core/dst.c index 656b70d39690..39cc11968cf9 100644 --- a/net/core/dst.c +++ b/net/core/dst.c @@ -470,6 +470,20 @@ 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) |