[PATCH v3 1/3] rcu/exp: Use NMI to get the backtrace of cpu_curr(other_cpu) first

[Zhen Lei]

The backtrace of cpu_curr(other_cpu) is unwinded based on the 'fp' saved
during its last switch-out. For the most part, it's out of date. So try
to use NMI to get the backtrace first, just like those functions in
"tree_stall.h" did. Such as rcu_dump_cpu_stacks().

Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
---
 kernel/rcu/tree_exp.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 0f70f62039a9090..21381697de23f0b 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -665,7 +665,8 @@ static void synchronize_rcu_expedited_wait(void)
 				mask = leaf_node_cpu_bit(rnp, cpu);
 				if (!(READ_ONCE(rnp->expmask) & mask))
 					continue;
-				dump_cpu_task(cpu);
+				if (!trigger_single_cpu_backtrace(cpu))
+					dump_cpu_task(cpu);
 			}
 		}
 		jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
-- 
2.25.1