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Date: Thu, 16 Jun 2016 07:19:20 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Ding Tianhong <dingtianhong@...wei.com> Cc: josh@...htriplett.org, rostedt@...dmis.org, mathieu.desnoyers@...icios.com, jiangshanlai@...il.com, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] rcu: Fix soft lockup for rcu_nocb_kthread On Thu, Jun 16, 2016 at 02:09:47PM +0800, Ding Tianhong wrote: > 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 Thank you! You were running with preemption disabled, so your system would indeed be very susceptible to this problem. > > 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. Please let me know how it goes! Thanx, Paul > Ding > > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > commit c317cf19b34c0d2787b787c38bd2c8fe433215da > > Author: Ding Tianhong <dingtianhong@...wei.com> > > 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@...wei.com> > > [ paulmck: Substituted cond_resched_rcu_qs for cond_resched. ] > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> > > > > 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); > > > > > > . > > > >
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