Commit-ID: 7aa92230c9e86b2150f718185f70e0af592e290b
Gitweb: http://git.kernel.org/tip/7aa92230c9e86b2150f718185f70e0af592e290b
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Tue, 29 Nov 2016 05:49:06 -0800
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon, 23 Jan 2017 11:37:12 -0800
rcu: Once again use NMI-based stack traces in stall warnings
This commit is for all intents and purposes a revert of bc1dce514e9b
("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 42a0bb3f7138
("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 bc1dce514e9b
("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@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
---
kernel/rcu/tree.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 5a4aaad..d7b63b8 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -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))
+ 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);
}
}
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