From: David Ahern <dsa@cumulusnetworks.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: steffen.klassert@secunet.com, netdev@vger.kernel.org,
Stephen Hemminger <stephen@networkplumber.org>
Subject: Re: [PATCH] net af_key: Fix RCU splat
Date: Thu, 20 Aug 2015 15:57:34 -0700 [thread overview]
Message-ID: <55D65B5E.4080407@cumulusnetworks.com> (raw)
In-Reply-To: <1440089462.6610.49.camel@edumazet-glaptop2.roam.corp.google.com>
On 8/20/15 9:51 AM, Eric Dumazet wrote:
> On Thu, 2015-08-20 at 08:51 -0700, David Ahern wrote:
>> Hit the following splat testing VRF change for ipsec:
>>
>> [ 113.475692] ===============================
>> [ 113.476194] [ INFO: suspicious RCU usage. ]
>> [ 113.476667] 4.2.0-rc6-1+deb7u2+clUNRELEASED #3.2.65-1+deb7u2+clUNRELEASED Not tainted
>> [ 113.477545] -------------------------------
>> [ 113.478013] /work/monster-14/dsa/kernel.git/include/linux/rcupdate.h:568 Illegal context switch in RCU read-side critical section!
>> [ 113.479288]
>> [ 113.479288] other info that might help us debug this:
>> [ 113.479288]
>> [ 113.480207]
>> [ 113.480207] rcu_scheduler_active = 1, debug_locks = 1
>> [ 113.480931] 2 locks held by setkey/6829:
>> [ 113.481371] #0: (&net->xfrm.xfrm_cfg_mutex){+.+.+.}, at: [<ffffffff814e9887>] pfkey_sendmsg+0xfb/0x213
>> [ 113.482509] #1: (rcu_read_lock){......}, at: [<ffffffff814e767f>] rcu_read_lock+0x0/0x6e
>> [ 113.483509]
>> [ 113.483509] stack backtrace:
>> [ 113.484041] CPU: 0 PID: 6829 Comm: setkey Not tainted 4.2.0-rc6-1+deb7u2+clUNRELEASED #3.2.65-1+deb7u2+clUNRELEASED
>> [ 113.485422] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5.1-0-g8936dbb-20141113_115728-nilsson.home.kraxel.org 04/01/2014
>> [ 113.486845] 0000000000000001 ffff88001d4c7a98 ffffffff81518af2 ffffffff81086962
>> [ 113.487732] ffff88001d538480 ffff88001d4c7ac8 ffffffff8107ae75 ffffffff8180a154
>> [ 113.488628] 0000000000000b30 0000000000000000 00000000000000d0 ffff88001d4c7ad8
>> [ 113.489525] Call Trace:
>> [ 113.489813] [<ffffffff81518af2>] dump_stack+0x4c/0x65
>> [ 113.490389] [<ffffffff81086962>] ? console_unlock+0x3d6/0x405
>> [ 113.491039] [<ffffffff8107ae75>] lockdep_rcu_suspicious+0xfa/0x103
>> [ 113.491735] [<ffffffff81064032>] rcu_preempt_sleep_check+0x45/0x47
>> [ 113.492442] [<ffffffff8106404d>] ___might_sleep+0x19/0x1c8
>> [ 113.493077] [<ffffffff81064268>] __might_sleep+0x6c/0x82
>> [ 113.493681] [<ffffffff81133190>] cache_alloc_debugcheck_before.isra.50+0x1d/0x24
>> [ 113.494508] [<ffffffff81134876>] kmem_cache_alloc+0x31/0x18f
>> [ 113.495149] [<ffffffff814012b5>] skb_clone+0x64/0x80
>> [ 113.495712] [<ffffffff814e6f71>] pfkey_broadcast_one+0x3d/0xff
>> [ 113.496380] [<ffffffff814e7b84>] pfkey_broadcast+0xb5/0x11e
>> [ 113.497024] [<ffffffff814e82d1>] pfkey_register+0x191/0x1b1
>> [ 113.497653] [<ffffffff814e9770>] pfkey_process+0x162/0x17e
>> [ 113.498274] [<ffffffff814e9895>] pfkey_sendmsg+0x109/0x213
>>
>> In pfkey_sendmsg the net mutex is taken and then pfkey_broadcast takes
>> the RCU lock. Fix by using GFP_ATOMIC for the allocation flag.
>>
>> Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
>> ---
>> net/key/af_key.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/key/af_key.c b/net/key/af_key.c
>> index b397f0aa9005..73527e7dd247 100644
>> --- a/net/key/af_key.c
>> +++ b/net/key/af_key.c
>> @@ -1670,7 +1670,7 @@ static int pfkey_register(struct sock *sk, struct sk_buff *skb, const struct sad
>> return -ENOBUFS;
>> }
>>
>> - pfkey_broadcast(supp_skb, GFP_KERNEL, BROADCAST_REGISTERED, sk, sock_net(sk));
>> + pfkey_broadcast(supp_skb, GFP_ATOMIC, BROADCAST_REGISTERED, sk, sock_net(sk));
>>
>> return 0;
>> }
>
> I would rather remove the useless rcu locking from pfkey_broadcast() if
> a mutex properly protects the thing.
rcu_read_lock was added by Stephen with 7f6b9dbd5afbd. It does not
appear the net->xfrm.xfrm_cfg_mutex mutex added by 283bc9f35bbbc
properly covers the locking. ie., the rcu_read_lock is needed.
David
next prev parent reply other threads:[~2015-08-20 22:57 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-20 15:51 [PATCH] net af_key: Fix RCU splat David Ahern
2015-08-20 16:51 ` Eric Dumazet
2015-08-20 22:57 ` David Ahern [this message]
2015-08-20 23:36 ` Eric Dumazet
2015-08-23 23:48 ` David Miller
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