Messages in this thread | | | Date | Wed, 16 Apr 2014 16:34:44 +0800 | From | "Li, ZhenHua" <> | Subject | Re: [PATCH 1/1] net: Add rtnl_lock for netif_device_attach/detach |
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The problem I am trying to fix is: when netif_device_attach/detached is called, it get a return value from netif_running, but at this moment, in another thread, the stat of this dev changes. But in netif_device_attach, it does not know stat changed, and this may cause bugs.
I think you are right, this patch cannot fix race with another thread that takes the lock. But that's what is happening now(with out this patch). I do not yet find a way to fix it completely.
And another problem is: we only need a lock for this dev , not full all dev. So how about adding a single lock for each net device?
Regards Zhenhua
On 04/16/2014 03:38 PM, Veaceslav Falico wrote: > On Wed, Apr 16, 2014 at 03:08:02PM +0800, Li, Zhen-Hua wrote: >> From: "Li, Zhen-Hua" <zhen-hual@hp.com> >> >> 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@hp.com> >> --- >> 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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