[PATCH 3.8 151/166] netvsc: don't flush peers notifying work during setting mtu

Kamal Mostafa
2014-01-15T21:52:45Z

From: Jason Wang <jasowang@redhat.com>

[ Upstream commit 50dc875f2e6e2e04aed3b3033eb0ac99192d6d02 ]

There's a possible deadlock if we flush the peers notifying work during setting
mtu:

[ 22.991149] ======================================================
[ 22.991173] [ INFO: possible circular locking dependency detected ]
[ 22.991198] 3.10.0-54.0.1.el7.x86_64.debug #1 Not tainted
[ 22.991219] -------------------------------------------------------
[ 22.991243] ip/974 is trying to acquire lock:
[ 22.991261] ((&(&net_device_ctx->dwork)->work)){+.+.+.}, at: [<ffffffff8108af95>] flush_work+0x5/0x2e0
[ 22.991307]
but task is already holding lock:
[ 22.991330] (rtnl_mutex){+.+.+.}, at: [<ffffffff81539deb>] rtnetlink_rcv+0x1b/0x40
[ 22.991367]
which lock already depends on the new lock.

[ 22.991398]
the existing dependency chain (in reverse order) is:
[ 22.991426]
-> #1 (rtnl_mutex){+.+.+.}:
[ 22.991449] [<ffffffff810dfdd9>] __lock_acquire+0xb19/0x1260
[ 22.991477] [<ffffffff810e0d12>] lock_acquire+0xa2/0x1f0
[ 22.991501] [<ffffffff81673659>] mutex_lock_nested+0x89/0x4f0
[ 22.991529] [<ffffffff815392b7>] rtnl_lock+0x17/0x20
[ 22.991552] [<ffffffff815230b2>] netdev_notify_peers+0x12/0x30
[ 22.991579] [<ffffffffa0340212>] netvsc_send_garp+0x22/0x30 [hv_netvsc]
[ 22.991610] [<ffffffff8108d251>] process_one_work+0x211/0x6e0
[ 22.991637] [<ffffffff8108d83b>] worker_thread+0x11b/0x3a0
[ 22.991663] [<ffffffff81095e5d>] kthread+0xed/0x100
[ 22.991686] [<ffffffff81681c6c>] ret_from_fork+0x7c/0xb0
[ 22.991715]
-> #0 ((&(&net_device_ctx->dwork)->work)){+.+.+.}:
[ 22.991715] [<ffffffff810de817>] check_prevs_add+0x967/0x970
[ 22.991715] [<ffffffff810dfdd9>] __lock_acquire+0xb19/0x1260
[ 22.991715] [<ffffffff810e0d12>] lock_acquire+0xa2/0x1f0
[ 22.991715] [<ffffffff8108afde>] flush_work+0x4e/0x2e0
[ 22.991715] [<ffffffff8108e1b5>] __cancel_work_timer+0x95/0x130
[ 22.991715] [<ffffffff8108e303>] cancel_delayed_work_sync+0x13/0x20
[ 22.991715] [<ffffffffa03404e4>] netvsc_change_mtu+0x84/0x200 [hv_netvsc]
[ 22.991715] [<ffffffff815233d4>] dev_set_mtu+0x34/0x80
[ 22.991715] [<ffffffff8153bc2a>] do_setlink+0x23a/0xa00
[ 22.991715] [<ffffffff8153d054>] rtnl_newlink+0x394/0x5e0
[ 22.991715] [<ffffffff81539eac>] rtnetlink_rcv_msg+0x9c/0x260
[ 22.991715] [<ffffffff8155cdd9>] netlink_rcv_skb+0xa9/0xc0
[ 22.991715] [<ffffffff81539dfa>] rtnetlink_rcv+0x2a/0x40
[ 22.991715] [<ffffffff8155c41d>] netlink_unicast+0xdd/0x190
[ 22.991715] [<ffffffff8155c807>] netlink_sendmsg+0x337/0x750
[ 22.991715] [<ffffffff8150d219>] sock_sendmsg+0x99/0xd0
[ 22.991715] [<ffffffff8150d63e>] ___sys_sendmsg+0x39e/0x3b0
[ 22.991715] [<ffffffff8150eba2>] __sys_sendmsg+0x42/0x80
[ 22.991715] [<ffffffff8150ebf2>] SyS_sendmsg+0x12/0x20
[ 22.991715] [<ffffffff81681d19>] system_call_fastpath+0x16/0x1b

This is because we hold the rtnl_lock() before ndo_change_mtu() and try to flush
the work in netvsc_change_mtu(), in the mean time, netdev_notify_peers() may be
called from worker and also trying to hold the rtnl_lock. This will lead the
flush won't succeed forever. Solve this by not canceling and flushing the work,
this is safe because the transmission done by NETDEV_NOTIFY_PEERS was
synchronized with the netif_tx_disable() called by netvsc_change_mtu().

Reported-by: Yaju Cao <yacao@redhat.com>
Tested-by: Yaju Cao <yacao@redhat.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
drivers/net/hyperv/netvsc_drv.c | 1 -
1 file changed, 1 deletion(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 8264f0e..d573483 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -327,7 +327,6 @@ static int netvsc_change_mtu(struct net_device *ndev, int mtu)
return -EINVAL;

nvdev->start_remove = true;
- cancel_delayed_work_sync(&ndevctx->dwork);
cancel_work_sync(&ndevctx->work);
netif_tx_disable(ndev);
rndis_filter_device_remove(hdev);
--
1.8.3.2