From c4402b27f1778fad0dbc27b2d88bb06ca22a06f0 Mon Sep 17 00:00:00 2001 From: Byungchul Park Date: Wed, 9 Nov 2016 17:57:13 +0900 Subject: [PATCH] rcu: Only dump stalled-tasks stacks if there was a real stall The print_other_cpu_stall() function currently unconditionally invokes rcu_print_detail_task_stall(). This is OK because if there was a stall sufficient to cause print_other_cpu_stall() to be invoked, that stall is very likely to persist through the entire print_other_cpu_stall() execution. However, if the stall did not persist, the variable ndetected will be zero, and that variable is already tested in an "if" statement. Therefore, this commit moves the call to rcu_print_detail_task_stall() under that pre-existing "if" to improve readability, with a very rare reduction in overhead. Signed-off-by: Byungchul Park [ paulmck: Reworked commit log. ] Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcu/tree.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index cb4e2056ccf3..6232d2f9a84e 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1379,6 +1379,9 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum) (long)rsp->gpnum, (long)rsp->completed, totqlen); if (ndetected) { rcu_dump_cpu_stacks(rsp); + + /* Complain about tasks blocking the grace period. */ + rcu_print_detail_task_stall(rsp); } else { if (READ_ONCE(rsp->gpnum) != gpnum || READ_ONCE(rsp->completed) == gpnum) { @@ -1395,9 +1398,6 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum) } } - /* Complain about tasks blocking the grace period. */ - rcu_print_detail_task_stall(rsp); - rcu_check_gp_kthread_starvation(rsp); panic_on_rcu_stall();