From 46d8696c613b4256f625ffd0cbeb88574e3c7033 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 9 Jan 2018 10:38:17 -0800 Subject: [PATCH] rcu: Call touch_nmi_watchdog() while printing stall warnings [ Upstream commit 3caa973b7a260e7a2a69edc94c300ab9c65148c3 ] When RCU stall warning triggers, it can print out a lot of messages while holding spinlocks. If the console device is slow (e.g. an actual or IPMI serial console), it may end up triggering NMI hard lockup watchdog like the following. --- kernel/rcu/tree_plugin.h | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index fed95fa941e6..8b3102d22823 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -559,8 +559,14 @@ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) } t = list_entry(rnp->gp_tasks->prev, struct task_struct, rcu_node_entry); - list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) + list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { + /* + * We could be printing a lot while holding a spinlock. + * Avoid triggering hard lockup. + */ + touch_nmi_watchdog(); sched_show_task(t); + } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } @@ -1677,6 +1683,12 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) char *ticks_title; unsigned long ticks_value; + /* + * We could be printing a lot while holding a spinlock. Avoid + * triggering hard lockup. + */ + touch_nmi_watchdog(); + if (rsp->gpnum == rdp->gpnum) { ticks_title = "ticks this GP"; ticks_value = rdp->ticks_this_gp;