Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 7aa92230 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarVince Weaver <vincent.weaver@maine.edu>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Reviewed-by: default avatarJosh 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);

	}

}