Commit 7aa92230 authored Nov 29, 2016 by Paul E. McKenney

rcu: Once again use NMI-based stack traces in stall warnings



This commit is for all intents and purposes a revert of bc1dce51
("rcu: Don't use NMIs to dump other CPUs' stacks").  The reason to suppose
that this can now safely be reverted is the presence of 42a0bb3f
("printk/nmi: generic solution for safe printk in NMI"), which is said
to have made NMI-based stack dumps safe.

However, this reversion keeps one nice property of bc1dce51
("rcu: Don't use NMIs to dump other CPUs' stacks"), namely that
only those CPUs blocking the grace period are dumped.  The new
trigger_single_cpu_backtrace() is used to make this happen, as
suggested by Josh Poimboeuf.

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

parent b201fa67

kernel/rcu/tree.c

+7 −5

Original line number	Diff line number	Diff line
		@@ -1278,7 +1278,10 @@ static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
		}

		/*
		* Dump stacks of all tasks running on stalled CPUs.
		* Dump stacks of all tasks running on stalled CPUs. First try using
		* NMIs, but fall back to manual remote stack tracing on architectures
		* that don't support NMI-based stack dumps. The NMI-triggered stack
		* traces are more accurate because they are printed by the target CPU.
		*/
		static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
		{
		@@ -1288,11 +1291,10 @@ static void rcu_dump_cpu_stacks(struct rcu_state *rsp)

		rcu_for_each_leaf_node(rsp, rnp) {
		raw_spin_lock_irqsave_rcu_node(rnp, flags);
		if (rnp->qsmask != 0) {
		for_each_leaf_node_possible_cpu(rnp, cpu)
		if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
		if (!trigger_single_cpu_backtrace(cpu))
		dump_cpu_task(cpu);
		}
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
		}
		}

Admin message