[PATCH net v2 2/5] hv_netvsc: avoid deadlocks between rtnl lock and vf_use_cnt wait
From: Vitaly Kuznetsov <vkuznets@redhat.com>
Date: 2016-08-15 15:48:54
Also in:
lkml
Subsystem:
hyper-v/azure core and drivers, networking drivers, the rest · Maintainers:
"K. Y. Srinivasan", Haiyang Zhang, Wei Liu, Dexuan Cui, Long Li, Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
Here is a deadlock scenario: - netvsc_vf_up() schedules netvsc_notify_peers() work and quits. - netvsc_vf_down() runs before netvsc_notify_peers() gets executed. As it is being executed from netdev notifier chain we hold rtnl lock when we get here. - we enter while (atomic_read(&net_device_ctx->vf_use_cnt) != 0) loop and wait till netvsc_notify_peers() drops vf_use_cnt. - netvsc_notify_peers() starts on some other CPU but netdev_notify_peers() will hang on rtnl_lock(). - deadlock! Instead of introducing additional synchronization I suggest we drop gwrk.dwrk completely and call NETDEV_NOTIFY_PEERS directly. As we're acting under rtnl lock this is legitimate. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Acked-by: Haiyang Zhang <haiyangz@microsoft.com> --- Changes since v1: - Move the patch ahead in the series to avoid introducing new blocking issues and solving them later in the series. [David Miller] --- drivers/net/hyperv/hyperv_net.h | 7 ------- drivers/net/hyperv/netvsc_drv.c | 33 +++++---------------------------- 2 files changed, 5 insertions(+), 35 deletions(-)
diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
index 3b3ecf2..591af71 100644
--- a/drivers/net/hyperv/hyperv_net.h
+++ b/drivers/net/hyperv/hyperv_net.h@@ -644,12 +644,6 @@ struct netvsc_reconfig { u32 event; }; -struct garp_wrk { - struct work_struct dwrk; - struct net_device *netdev; - struct net_device_context *net_device_ctx; -}; - /* The context of the netvsc device */ struct net_device_context { /* point back to our device context */
@@ -667,7 +661,6 @@ struct net_device_context { struct work_struct work; u32 msg_enable; /* debug level */ - struct garp_wrk gwrk; struct netvsc_stats __percpu *tx_stats; struct netvsc_stats __percpu *rx_stats;
diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 794139b..70317fa 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c@@ -1151,17 +1151,6 @@ static void netvsc_free_netdev(struct net_device *netdev) free_netdev(netdev); } -static void netvsc_notify_peers(struct work_struct *wrk) -{ - struct garp_wrk *gwrk; - - gwrk = container_of(wrk, struct garp_wrk, dwrk); - - netdev_notify_peers(gwrk->netdev); - - atomic_dec(&gwrk->net_device_ctx->vf_use_cnt); -} - static struct net_device *get_netvsc_net_device(char *mac) { struct net_device *dev, *found = NULL;
@@ -1253,15 +1242,8 @@ static int netvsc_vf_up(struct net_device *vf_netdev) netif_carrier_off(ndev); - /* - * Now notify peers. We are scheduling work to - * notify peers; take a reference to prevent - * the VF interface from vanishing. - */ - atomic_inc(&net_device_ctx->vf_use_cnt); - net_device_ctx->gwrk.netdev = vf_netdev; - net_device_ctx->gwrk.net_device_ctx = net_device_ctx; - schedule_work(&net_device_ctx->gwrk.dwrk); + /* Now notify peers through VF device. */ + call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, vf_netdev); return NOTIFY_OK; }
@@ -1300,13 +1282,9 @@ static int netvsc_vf_down(struct net_device *vf_netdev) netdev_info(ndev, "Data path switched from VF: %s\n", vf_netdev->name); rndis_filter_close(netvsc_dev); netif_carrier_on(ndev); - /* - * Notify peers. - */ - atomic_inc(&net_device_ctx->vf_use_cnt); - net_device_ctx->gwrk.netdev = ndev; - net_device_ctx->gwrk.net_device_ctx = net_device_ctx; - schedule_work(&net_device_ctx->gwrk.dwrk); + + /* Now notify peers through netvsc device. */ + call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, ndev); return NOTIFY_OK; }
@@ -1378,7 +1356,6 @@ static int netvsc_probe(struct hv_device *dev, INIT_DELAYED_WORK(&net_device_ctx->dwork, netvsc_link_change); INIT_WORK(&net_device_ctx->work, do_set_multicast); - INIT_WORK(&net_device_ctx->gwrk.dwrk, netvsc_notify_peers); spin_lock_init(&net_device_ctx->lock); INIT_LIST_HEAD(&net_device_ctx->reconfig_events);
--
2.7.4