From: Stephen Hemminger <shemminger@vyatta.com>
To: "Akkipeddi, Srinivas" <sakkiped@starentnetworks.com>
Cc: <netdev@vger.kernel.org>,
"Johnson, David" <djohnson@starentnetworks.com>
Subject: Re: Deadlock in IPv6 code while garbage collection on the rwlock protecting the routing tree.
Date: Tue, 22 Dec 2009 14:36:38 -0800 [thread overview]
Message-ID: <20091222143638.37513a94@nehalam> (raw)
In-Reply-To: <4D35478224365146822AE9E3AD4A26660E89A49E@exchtewks3.starentnetworks.com>
On Tue, 22 Dec 2009 16:57:05 -0500
"Akkipeddi, Srinivas" <sakkiped@starentnetworks.com> wrote:
> I came across a deadlock scenario in the latest IPv6 code. I am trying
> to fix this and any inputs are really appreciated.
>
> The deadlock happens when ROUTER-PREF is configured. This happens when
> trying to do a write_lock_bh on the rwlock protecting the routing tree
> during garbage collection.
>
> The routing tree is read protected (read_lock_bh(&table->tb6_lock))
> using the rwlock when performing a ip6_route_input or ip6_route_output
> ( "ip6_pol_route"). During route selection (rt6_select), if a neighbor
> solicit is sent (ndisc_send_ns), a dst_entry is allocated
> (icmp6_dst_alloc calls dst_alloc).
> The garbage collection (fib6_run_gc) will be triggered if the number of
> dst-entries is more than the threshold (dst_alloc). During garbage
> collection, all the routing trees are cleaned up (fib6_clean_all). Here
> we try to take write protect each routing tree (
> write_lock_bh(&table->tb6_lock)). But one of the trees is already read
> protected.
>
> The garbage collection is anyways triggered from "icmp6_dst_alloc" with
> the call to fib6_force_start_gc. Since it is triggered, we might not
> want to call the "fib6_run_gc" from dst_alloc for this case but there is
> no way to figure this out in the "dst_alloc" routine.
Might just be easier to convert to spinlock and RCU.
--
next prev parent reply other threads:[~2009-12-22 22:37 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-12-22 21:57 Deadlock in IPv6 code while garbage collection on the rwlock protecting the routing tree Akkipeddi, Srinivas
2009-12-22 22:36 ` Stephen Hemminger [this message]
2009-12-23 17:44 ` Dave Johnson
2009-12-23 18:13 ` Stephen Hemminger
2010-01-23 10:22 ` David Miller
2010-01-26 9:48 ` Jarek Poplawski
2010-01-26 10:35 ` Jarek Poplawski
2010-01-27 9:59 ` [PATCH] ipv6: Fix possible NULL dereference in icmp6_dst_alloc Jarek Poplawski
2010-01-27 10:14 ` David Miller
2010-01-27 10:34 ` Jarek Poplawski
2010-01-27 11:04 ` David Miller
2010-01-27 12:17 ` Jarek Poplawski
2010-01-27 12:23 ` David Miller
2010-01-27 12:43 ` Jarek Poplawski
2010-01-27 13:14 ` David Miller
2010-01-27 13:28 ` Jarek Poplawski
2010-01-27 12:35 ` Atis Elsts
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