netdev - Re: [PATCH] can: Fix kernel panic at security_sock_rcv

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Message-ID: <20170114034330.GA30070@shuo-desktop.sh.intel.com>
Date:   Sat, 14 Jan 2017 11:43:30 +0800
From:   Liu Shuo <shuo.a.liu@...el.com>
To:     Oliver Hartkopp <socketcan@...tkopp.net>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        linux-kernel@...r.kernel.org, yanmin_zhang@...ux.intel.com,
        shuox.liu@...il.com, Zhang Yanmin <yanmin.zhang@...el.com>,
        "He, Bo" <bo.he@...el.com>, Marc Kleine-Budde <mkl@...gutronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        "open list:CAN NETWORK LAYER" <linux-can@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>
Subject: Re: [PATCH] can: Fix kernel panic at security_sock_rcv_skb

On Thu 12.Jan'17 at 17:33:38 +0100, Oliver Hartkopp wrote:
>On 01/12/2017 02:01 PM, Eric Dumazet wrote:
>>On Thu, 2017-01-12 at 09:22 +0100, Oliver Hartkopp wrote:
>
>>>But my main concern is:
>>>
>>>The reason why can_rx_delete_receiver() was introduced was the need to
>>>remove a huge number of receivers with can_rx_unregister().
>>>
>>>When you call synchronize_rcu() after each receiver removal this would
>>>potentially lead to a big performance issue when e.g. closing CAN_RAW
>>>sockets with a high number of receivers.
>>>
>>>So the idea was to remove/unlink the receiver hlist_del_rcu(&r->list)
>>>and also kmem_cache_free(rcv_cache, r) by some rcu mechanism - so that
>>>all elements are cleaned up by rcu at a later point.
>>>
>>>Is it possible that the problems emerge due to hlist_del_rcu(&r->list)
>>>and you accidently fix it with your introduced synchronize_rcu()?
>>
>>I agree this patch does not fix the root cause.
>>
>>The main problem seems that the sockets themselves are not RCU
>>protected.
>>
>>If CAN uses RCU for delivery, then sockets should be freed only after
>>one RCU grace period.
>>
>>On recent kernels, following patch could help :
>>
>
>Thanks Eric!
>
>@Liu ShuoX: Can you check if Eric's suggestion fixes the issue in your 
>setup?
Sorry for late reply. I was OOO yesterday.
With Eric's hint, i just found his patch that "net: add SOCK_RCU_FREE
socket flag" in the latest kernel. With backporting this one plus Eric's
following patch, it fixs my failure.

Thanks Eric and Oliver!

Shuo
>
>Best regards,
>Oliver