netdev - Re: [PATCH] net: fix lockdep issue in __neigh_event

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Date:	Mon, 19 Sep 2011 23:03:27 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Maciej Żenczykowski <zenczykowski@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	MuraliRaja Muniraju <muralira@...gle.com>
Subject: Re: [PATCH] net: fix lockdep issue in __neigh_event_send

Le lundi 19 septembre 2011 à 22:46 +0200, Eric Dumazet a écrit :
> Le lundi 19 septembre 2011 à 13:39 -0700, Maciej Żenczykowski a écrit :
> > [   90.544012] the existing dependency chain (in reverse order) is:
> > [   90.544012]
> > [   90.544012] -> #2 (&(&rt_hash_locks[i])->rlock){+.-...}:
> > [   90.544012]        [<ffffffff810a4910>] __lock_acquire+0xb3b/0xcda
> > [   90.544012]        [<ffffffff810a4b72>] lock_acquire+0xc3/0xe9
> > [   90.544012]        [<ffffffff81430d66>] _raw_spin_lock_bh+0x36/0x45
> > [   90.544012]        [<ffffffff813d9659>] rt_dst_release+0x4a/0x8d

rt_dst_release() again...

> > [   90.544012]        [<ffffffff813bee34>] dst_release+0x5d/0x66
> > [   90.544012]        [<ffffffff813af24e>] skb_release_head_state+0x1f/0xa5
> > [   90.544012]        [<ffffffff813aefec>] __kfree_skb+0x16/0x87
> > [   90.544012]        [<ffffffff813af101>] kfree_skb+0x72/0x7a
> > [   90.544012]        [<ffffffff813c06f9>] __neigh_event_send+0x126/0x176
> > 

> Hmm
> 
> What exact kernel version is it ?
> 
> 

Just to say what I already said to Murali raja Muniraju one week ago :

To my knowledge, no linux pristine linux kernel has this bug.

dst_release() is lockless.

So could you explain why its so important we add this 'bugfix' if it
only applies to a Google kernel ?

Anything I missed from my previous analysis ?

Thanks !


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