linux-kernel - [for-linus][PATCH 5/7] ftrace: Avoid synchronize_rcu_tasks

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20210723125634.213430293@goodmis.org>
Date:   Fri, 23 Jul 2021 08:54:59 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicolas Saenz Julienne <nsaenzju@...hat.com>
Subject: [for-linus][PATCH 5/7] ftrace: Avoid synchronize_rcu_tasks_rude() call when not necessary

From: Nicolas Saenz Julienne <nsaenzju@...hat.com>

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@...hat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 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 e6fb3e6e1ffc..4fbcf560dd03 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);
 	}
-- 
2.30.2