netdev - Re: [PATCH 1/2] ipv6 mcast: use del_timer_sync instead of del_timer in ipv6_mc

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Date:	Tue, 10 Sep 2013 11:20:18 -0700
From:	Salam Noureddine <noureddine@...stanetworks.com>
To:	Ben Hutchings <bhutchings@...arflare.com>, netdev@...r.kernel.org
Cc:	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH 1/2] ipv6 mcast: use del_timer_sync instead of del_timer
 in ipv6_mc_down

I ran our usual workload with lockdep enabled and didn't see any
lockdep complaints.
Another approach to solve this would be to use in6_dev_put instead of
__in6_dev_put
int the multicast code. I am not sure though why __in6_dev_put was
originally used.
This part of the code seems to not have been changed since the initial
git check-in.

Thanks,

Salam

On Thu, Sep 5, 2013 at 10:20 AM, Salam Noureddine
<noureddine@...stanetworks.com> wrote:
> On Thu, Sep 5, 2013 at 7:30 AM, Ben Hutchings <bhutchings@...arflare.com> wrote:
>>> diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
>>> index 99cd65c..5c8d49d 100644
>>> --- a/net/ipv6/mcast.c
>>> +++ b/net/ipv6/mcast.c
>>> @@ -2277,12 +2277,12 @@ void ipv6_mc_down(struct inet6_dev *idev)
>>>
>>>       read_lock_bh(&idev->lock);
>>>       idev->mc_ifc_count = 0;
>>> -     if (del_timer(&idev->mc_ifc_timer))
>>> +     if (del_timer_sync(&idev->mc_ifc_timer))
>>
>> Are you sure this doesn't introduce a potential deadlock?  Have you
>> tested this with lockdep enabled?
>>
>> Ben.
>
> I will test with lockdep enabled and get back to you.
>
> Thanks,
>
> Salam
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