On Wed, Apr 16, 2014 at 03:08:02PM +0800, Li, Zhen-Hua wrote:
From: "Li, Zhen-Hua" <zhen-hual@xxxxxx> As netif_running is called in netif_device_attach/detach. There should be rtnl_lock/unlock called, to avoid dev stat change during netif_device_attach and detach being called. I checked NIC some drivers, some of them have netif_device_attach/detach called between rtnl_lock/unlock, while some drivers do not.
It can race with any other thread that takes the lock - i.e. suppose you have a driver that doesn't take the lock and calls netif_device_attach(), while another thread (completely unrelated to the issue) holds rtnl_lock - this way the trylock will return false, the thread that took rtnl releases it - and you'll see the exact same behaviour as without your patch. I'm not sure about the issue you're trying to fix here - there might be a better approach which I'm not aware of, however with your approach you should really either remove the rtnl locking from all drivers that use this function (and insert a normal rtnl_lock here) or, vice-versa, add it to all drivers and add an ASSERT_RTNL to netif_device_detach/attach.
This patch is tring to find a generic way to fix this for all NIC drivers. Signed-off-by: Li, Zhen-Hua <zhen-hual@xxxxxx> --- net/core/dev.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/net/core/dev.c b/net/core/dev.c index 5b3042e..795bbc5 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -2190,10 +2190,19 @@ EXPORT_SYMBOL(__dev_kfree_skb_any); */ void netif_device_detach(struct net_device *dev) { + /** + * As netif_running is called , rtnl_lock and unlock are needed to + * avoid __LINK_STATE_START bit changes during this function call. + */ + int need_unlock; + + need_unlock = rtnl_trylock(); if (test_and_clear_bit(__LINK_STATE_PRESENT, &dev->state) && netif_running(dev)) { netif_tx_stop_all_queues(dev); } + if (need_unlock) + rtnl_unlock(); } EXPORT_SYMBOL(netif_device_detach); @@ -2205,11 +2214,20 @@ EXPORT_SYMBOL(netif_device_detach); */ void netif_device_attach(struct net_device *dev) { + /** + * As netif_running is called , rtnl_lock and unlock are needed to + * avoid __LINK_STATE_START bit changes during this function call. + */ + int need_unlock; + + need_unlock = rtnl_trylock(); if (!test_and_set_bit(__LINK_STATE_PRESENT, &dev->state) && netif_running(dev)) { netif_tx_wake_all_queues(dev); __netdev_watchdog_up(dev); } + if (need_unlock) + rtnl_unlock(); } EXPORT_SYMBOL(netif_device_attach); -- 1.7.10.4
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