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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 <nsaenzju@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Nicolas Saenz Julienne 2021-07-21 13:47:26 +02:00 committed by Steven Rostedt (VMware)
parent 9528c19507
commit 68e83498cb
1 changed files with 2 additions and 1 deletions
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3
kernel/trace/ftrace.c
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@ -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);
}