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Date:	Sun, 6 Sep 2015 16:00:50 +0800
From:	Ying Xue <ying.xue@...driver.com>
To:	Kolmakov Dmitriy <kolmakov.dmitriy@...wei.com>,
	"davem@...emloft.net" <davem@...emloft.net>
CC:	"jon.maloy@...csson.com" <jon.maloy@...csson.com>,
	"tipc-discussion@...ts.sourceforge.net" 
	<tipc-discussion@...ts.sourceforge.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: tipc: fix stall during bclink wakeup procedure

On 09/03/2015 10:39 PM, Kolmakov Dmitriy wrote:
> From: Dmitry S Kolmakov <kolmakov.dmitriy@...wei.com>
>  
> If an attempt to wake up users of broadcast link is made when there is
> no enough place in send queue than it may hang up inside the
> tipc_sk_rcv() function since the loop breaks only after the wake up
> queue becomes empty. This can lead to complete CPU stall with the
> following message generated by RCU:
>  
> INFO: rcu_sched self-detected stall on CPU { 0}  (t=2101 jiffies g=54225 c=54224 q=11465)
> Task dump for CPU 0:
> tpch            R  running task        0 39949  39948 0x0000000a
>  ffffffff818536c0 ffff88181fa037a0 ffffffff8106a4be 0000000000000000
>  ffffffff818536c0 ffff88181fa037c0 ffffffff8106d8a8 ffff88181fa03800
>  0000000000000001 ffff88181fa037f0 ffffffff81094a50 ffff88181fa15680
> Call Trace:
>  <IRQ>  [<ffffffff8106a4be>] sched_show_task+0xae/0x120
>  [<ffffffff8106d8a8>] dump_cpu_task+0x38/0x40
>  [<ffffffff81094a50>] rcu_dump_cpu_stacks+0x90/0xd0
>  [<ffffffff81097c3b>] rcu_check_callbacks+0x3eb/0x6e0
>  [<ffffffff8106e53f>] ? account_system_time+0x7f/0x170
>  [<ffffffff81099e64>] update_process_times+0x34/0x60
>  [<ffffffff810a84d1>] tick_sched_handle.isra.18+0x31/0x40
>  [<ffffffff810a851c>] tick_sched_timer+0x3c/0x70
>  [<ffffffff8109a43d>] __run_hrtimer.isra.34+0x3d/0xc0
>  [<ffffffff8109aa95>] hrtimer_interrupt+0xc5/0x1e0
>  [<ffffffff81030d52>] ? native_smp_send_reschedule+0x42/0x60
>  [<ffffffff81032f04>] local_apic_timer_interrupt+0x34/0x60
>  [<ffffffff810335bc>] smp_apic_timer_interrupt+0x3c/0x60
>  [<ffffffff8165a3fb>] apic_timer_interrupt+0x6b/0x70
>  [<ffffffff81659129>] ? _raw_spin_unlock_irqrestore+0x9/0x10
>  [<ffffffff8107eb9f>] __wake_up_sync_key+0x4f/0x60
>  [<ffffffffa313ddd1>] tipc_write_space+0x31/0x40 [tipc]
>  [<ffffffffa313dadf>] filter_rcv+0x31f/0x520 [tipc]
>  [<ffffffffa313d699>] ? tipc_sk_lookup+0xc9/0x110 [tipc]
>  [<ffffffff81659259>] ? _raw_spin_lock_bh+0x19/0x30
>  [<ffffffffa314122c>] tipc_sk_rcv+0x2dc/0x3e0 [tipc]
>  [<ffffffffa312e7ff>] tipc_bclink_wakeup_users+0x2f/0x40 [tipc]
>  [<ffffffffa313ce26>] tipc_node_unlock+0x186/0x190 [tipc]
>  [<ffffffff81597c1c>] ? kfree_skb+0x2c/0x40
>  [<ffffffffa313475c>] tipc_rcv+0x2ac/0x8c0 [tipc]
>  [<ffffffffa312ff58>] tipc_l2_rcv_msg+0x38/0x50 [tipc]
>  [<ffffffff815a76d3>] __netif_receive_skb_core+0x5a3/0x950
>  [<ffffffff815a98d3>] __netif_receive_skb+0x13/0x60
>  [<ffffffff815a993e>] netif_receive_skb_internal+0x1e/0x90
>  [<ffffffff815aa138>] napi_gro_receive+0x78/0xa0
>  [<ffffffffa07f93f4>] tg3_poll_work+0xc54/0xf40 [tg3]
>  [<ffffffff81597c8c>] ? consume_skb+0x2c/0x40
>  [<ffffffffa07f9721>] tg3_poll_msix+0x41/0x160 [tg3]
>  [<ffffffff815ab0f2>] net_rx_action+0xe2/0x290
>  [<ffffffff8104b92a>] __do_softirq+0xda/0x1f0
>  [<ffffffff8104bc26>] irq_exit+0x76/0xa0
>  [<ffffffff81004355>] do_IRQ+0x55/0xf0
>  [<ffffffff8165a12b>] common_interrupt+0x6b/0x6b
>  <EOI>
> 
> The issue occurs only when tipc_sk_rcv() is used to wake up postponed senders:
> 
> 	tipc_bclink_wakeup_users()
> 		// wakeupq - is a queue which consists of special 
> 		// 		 messages with SOCK_WAKEUP type. 
> 		tipc_sk_rcv(wakeupq)
> 			...
> 			while (skb_queue_len(inputq)) {
> 				filter_rcv(skb)
> 					// Here the type of message is checked 
> 					// and if it is SOCK_WAKEUP than

s/than/then

> 					// it tries to wake up a sender.
> 					tipc_write_space(sk)
> 						wake_up_interruptible_sync_poll()
> 			}
> 				
> After the sender thread is woke up it can gather control and perform an attempt to send a message. But if there is no enough place in send queue it will call link_schedule_user() function which puts a message of type SOCK_WAKEUP to the wakeup queue and put the sender to sleep. Thus the size of the queue actually is not changed and the while() loop never exits. 
> 
> The approach I proposed is to wake up only senders for which there is enough place in send queue so the described issue can't occur. Moreover the same approach is already used to wake up senders on unicast links.
> 
> I have got into the issue on our product code but to reproduce the issue I changed a benchmark test application (from tipcutils/demos/benchmark) to perform the following scenario:
> 	1. Run 64 instances of test application (nodes). It can be done on the one physical machine.
> 	2. Each application connects to all other using TIPC sockets in RDM mode.
> 	3. When setup is done all nodes start simultaneously send broadcast messages. 
> 	4. Everything hangs up.
> 
> The issue is reproducible only when a congestion on broadcast link occurs. For example, when there are only 8 nodes it works fine since congestion doesn't occur. Send queue limit is 40 in my case (I use a critical importance level) and when 64 nodes send a message at the same moment a congestion occurs every time.
> 

Please don't let above maximum line length exceed 70 chars.

Acked-by: Ying Xue <ying.xue@...driver.com>

> Signed-off-by: Dmitry S Kolmakov <kolmakov.dmitriy@...wei.com>
> ---
> diff --git a/net/tipc/bcast.c b/net/tipc/bcast.c
> index c5cbdcb..997dd60 100644
> --- a/net/tipc/bcast.c
> +++ b/net/tipc/bcast.c
> @@ -169,6 +169,30 @@ static void bclink_retransmit_pkt(struct tipc_net *tn, u32 after, u32 to)
>  }
>  
>  /**
> + * bclink_prepare_wakeup - prepare users for wakeup after congestion
> + * @bcl: broadcast link
> + * @resultq: queue for users which can be woken up
> + * Move a number of waiting users, as permitted by available space in
> + * the send queue, from link wait queue to specified queue for wakeup
> + */
> +static void bclink_prepare_wakeup(struct tipc_link *bcl, struct sk_buff_head *resultq)
> +{
> +	int pnd[TIPC_SYSTEM_IMPORTANCE + 1] = {0,};
> +	int imp, lim;
> +	struct sk_buff *skb, *tmp;
> +
> +	skb_queue_walk_safe(&bcl->wakeupq, skb, tmp) {
> +		imp = TIPC_SKB_CB(skb)->chain_imp;
> +		lim = bcl->window + bcl->backlog[imp].limit;
> +		pnd[imp] += TIPC_SKB_CB(skb)->chain_sz;
> +		if ((pnd[imp] + bcl->backlog[imp].len) >= lim)
> +			continue;
> +		skb_unlink(skb, &bcl->wakeupq);
> +		skb_queue_tail(resultq, skb);
> +	}
> +}
> +
> +/**
>   * tipc_bclink_wakeup_users - wake up pending users
>   *
>   * Called with no locks taken
> @@ -176,8 +200,12 @@ static void bclink_retransmit_pkt(struct tipc_net *tn, u32 after, u32 to)
>  void tipc_bclink_wakeup_users(struct net *net)
>  {
>  	struct tipc_net *tn = net_generic(net, tipc_net_id);
> +	struct tipc_link *bcl = tn->bcl;
> +	struct sk_buff_head resultq;
>  
> -	tipc_sk_rcv(net, &tn->bclink->link.wakeupq);
> +	skb_queue_head_init(&resultq);
> +	bclink_prepare_wakeup(bcl, &resultq);
> +	tipc_sk_rcv(net, &resultq);
>  }
>  
>  /**
> 
> 

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