Re: [PATCH] rcu: Fix soft lockup for rcu_nocb_kthread

From: Ding Tianhong
Date: Thu Jun 16 2016 - 02:11:48 EST

On 2016/6/15 23:49, Paul E. McKenney wrote:
> On Wed, Jun 15, 2016 at 03:27:36PM +0800, Ding Tianhong wrote:
>> I met this problem when using the Testgine to send package to ixgbevf nic
>> by this steps:
>> 1. Connect to ixgbevf, and set the speed to 10Gb/s, it could work fine.
>> 2. Then use ifconfig to down the nic and up again, loop for several times.
>> 3. The system panic by soft lockup.
>
> Good catch, queued for review and testing. But what .config was your
> kernel built with?
>

I use the redhat7.1 defconfig to build my kernel, and the RCU config is this:
120 #
121 # RCU Subsystem
122 #
123 CONFIG_TREE_RCU=y
124 # CONFIG_PREEMPT_RCU is not set
125 CONFIG_RCU_STALL_COMMON=y
126 CONFIG_CONTEXT_TRACKING=y
127 CONFIG_RCU_USER_QS=y
128 # CONFIG_CONTEXT_TRACKING_FORCE is not set
129 CONFIG_RCU_FANOUT=64
130 CONFIG_RCU_FANOUT_LEAF=16
131 # CONFIG_RCU_FANOUT_EXACT is not set
132 # CONFIG_RCU_FAST_NO_HZ is not set
133 # CONFIG_TREE_RCU_TRACE is not set
134 CONFIG_RCU_NOCB_CPU=y
135 CONFIG_RCU_NOCB_CPU_ALL=y
136 CONFIG_BUILD_BIN2C=y


> Also, I did tweak both the commit log and the patch. Your cond_resched()
> would prevent soft lockups, but not RCU stalls, so I substituted
> cond_resched_rcu_qs(). Please let me know if either of those changes
> causes problems at your end.

Looks fine to me, I will apply this to my branch and test it, thanks.

Ding

>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit c317cf19b34c0d2787b787c38bd2c8fe433215da
> Author: Ding Tianhong <dingtianhong@xxxxxxxxxx>
> Date: Wed Jun 15 15:27:36 2016 +0800
>
> rcu: Fix soft lockup for rcu_nocb_kthread
>
> Carrying out the following steps results in a softlockup in the
> RCU callback-offload (rcuo) kthreads:
>
> 1. Connect to ixgbevf, and set the speed to 10Gb/s.
> 2. Use ifconfig to bring the nic up and down repeatedly.
>
> [ 317.005148] IPv6: ADDRCONF(NETDEV_CHANGE): eth2: link becomes ready
> [ 368.106005] BUG: soft lockup - CPU#1 stuck for 22s! [rcuos/1:15]
> [ 368.106005] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> [ 368.106005] task: ffff88057dd8a220 ti: ffff88057dd9c000 task.ti: ffff88057dd9c000
> [ 368.106005] RIP: 0010:[<ffffffff81579e04>] [<ffffffff81579e04>] fib_table_lookup+0x14/0x390
> [ 368.106005] RSP: 0018:ffff88061fc83ce8 EFLAGS: 00000286
> [ 368.106005] RAX: 0000000000000001 RBX: 00000000020155c0 RCX: 0000000000000001
> [ 368.106005] RDX: ffff88061fc83d50 RSI: ffff88061fc83d70 RDI: ffff880036d11a00
> [ 368.106005] RBP: ffff88061fc83d08 R08: 0000000000000001 R09: 0000000000000000
> [ 368.106005] R10: ffff880036d11a00 R11: ffffffff819e0900 R12: ffff88061fc83c58
> [ 368.106005] R13: ffffffff816154dd R14: ffff88061fc83d08 R15: 00000000020155c0
> [ 368.106005] FS: 0000000000000000(0000) GS:ffff88061fc80000(0000) knlGS:0000000000000000
> [ 368.106005] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 368.106005] CR2: 00007f8c2aee9c40 CR3: 000000057b222000 CR4: 00000000000407e0
> [ 368.106005] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 368.106005] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [ 368.106005] Stack:
> [ 368.106005] 00000000010000c0 ffff88057b766000 ffff8802e380b000 ffff88057af03e00
> [ 368.106005] ffff88061fc83dc0 ffffffff815349a6 ffff88061fc83d40 ffffffff814ee146
> [ 368.106005] ffff8802e380af00 00000000e380af00 ffffffff819e0900 020155c0010000c0
> [ 368.106005] Call Trace:
> [ 368.106005] <IRQ>
> [ 368.106005]
> [ 368.106005] [<ffffffff815349a6>] ip_route_input_noref+0x516/0xbd0
> [ 368.106005] [<ffffffff814ee146>] ? skb_release_data+0xd6/0x110
> [ 368.106005] [<ffffffff814ee20a>] ? kfree_skb+0x3a/0xa0
> [ 368.106005] [<ffffffff8153698f>] ip_rcv_finish+0x29f/0x350
> [ 368.106005] [<ffffffff81537034>] ip_rcv+0x234/0x380
> [ 368.106005] [<ffffffff814fd656>] __netif_receive_skb_core+0x676/0x870
> [ 368.106005] [<ffffffff814fd868>] __netif_receive_skb+0x18/0x60
> [ 368.106005] [<ffffffff814fe4de>] process_backlog+0xae/0x180
> [ 368.106005] [<ffffffff814fdcb2>] net_rx_action+0x152/0x240
> [ 368.106005] [<ffffffff81077b3f>] __do_softirq+0xef/0x280
> [ 368.106005] [<ffffffff8161619c>] call_softirq+0x1c/0x30
> [ 368.106005] <EOI>
> [ 368.106005]
> [ 368.106005] [<ffffffff81015d95>] do_softirq+0x65/0xa0
> [ 368.106005] [<ffffffff81077174>] local_bh_enable+0x94/0xa0
> [ 368.106005] [<ffffffff81114922>] rcu_nocb_kthread+0x232/0x370
> [ 368.106005] [<ffffffff81098250>] ? wake_up_bit+0x30/0x30
> [ 368.106005] [<ffffffff811146f0>] ? rcu_start_gp+0x40/0x40
> [ 368.106005] [<ffffffff8109728f>] kthread+0xcf/0xe0
> [ 368.106005] [<ffffffff810971c0>] ? kthread_create_on_node+0x140/0x140
> [ 368.106005] [<ffffffff816147d8>] ret_from_fork+0x58/0x90
> [ 368.106005] [<ffffffff810971c0>] ? kthread_create_on_node+0x140/0x140
>
> ==================================cut here==============================
>
> It turns out that the rcuos callback-offload kthread is busy processing
> a very large quantity of RCU callbacks, and it is not reliquishing the
> CPU while doing so. This commit therefore adds an cond_resched_rcu_qs()
> within the loop to allow other tasks to run.
>
> Signed-off-by: Ding Tianhong <dingtianhong@xxxxxxxxxx>
> [ paulmck: Substituted cond_resched_rcu_qs for cond_resched. ]
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
>
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 0082fce402a0..85c5a883c6e3 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2173,6 +2173,7 @@ static int rcu_nocb_kthread(void *arg)
> cl++;
> c++;
> local_bh_enable();
> + cond_resched_rcu_qs();
> list = next;
> }
> trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
>
>
> .
>