From 68e83498cb4fad31963b5c76a71e80b824bc316e Mon Sep 17 00:00:00 2001 From: Nicolas Saenz Julienne Date: Wed, 21 Jul 2021 13:47:26 +0200 Subject: [PATCH] ftrace: Avoid synchronize_rcu_tasks_rude() call when not necessary synchronize_rcu_tasks_rude() triggers IPIs and forces rescheduling on all CPUs. It is a costly operation and, when targeting nohz_full CPUs, very disrupting (hence the name). So avoid calling it when 'old_hash' doesn't need to be freed. Link: https://lkml.kernel.org/r/20210721114726.1545103-1-nsaenzju@redhat.com Signed-off-by: Nicolas Saenz Julienne Signed-off-by: Steven Rostedt (VMware) --- kernel/trace/ftrace.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index e6fb3e6..4fbcf56 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -5985,7 +5985,8 @@ ftrace_graph_release(struct inode *inode, struct file *file) * infrastructure to do the synchronization, thus we must do it * ourselves. */ - synchronize_rcu_tasks_rude(); + if (old_hash != EMPTY_HASH) + synchronize_rcu_tasks_rude(); free_ftrace_hash(old_hash); } -- 2.7.4