linux-kernel - [PATCH RT 17/32] lib/smp_processor_id: Dont use cpumask

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: <20200117174129.945230768@goodmis.org>
Date:   Fri, 17 Jan 2020 12:41:28 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org,
        linux-rt-users <linux-rt-users@...r.kernel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        John Kacur <jkacur@...hat.com>,
        Julia Cartwright <julia@...com>,
        Daniel Wagner <wagi@...om.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH RT 17/32] lib/smp_processor_id: Dont use cpumask_equal()

4.19.94-rt39-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Waiman Long <longman@...hat.com>

[ Upstream commit 659252061477862f45b79e1de169e6030f5c8918 ]

The check_preemption_disabled() function uses cpumask_equal() to see
if the task is bounded to the current CPU only. cpumask_equal() calls
memcmp() to do the comparison. As x86 doesn't have __HAVE_ARCH_MEMCMP,
the slow memcmp() function in lib/string.c is used.

On a RT kernel that call check_preemption_disabled() very frequently,
below is the perf-record output of a certain microbenchmark:

  42.75%  2.45%  testpmd [kernel.kallsyms] [k] check_preemption_disabled
  40.01% 39.97%  testpmd [kernel.kallsyms] [k] memcmp

We should avoid calling memcmp() in performance critical path. So the
cpumask_equal() call is now replaced with an equivalent simpler check.

Signed-off-by: Waiman Long <longman@...hat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 lib/smp_processor_id.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c
index fb35c45b9421..b8a8a8db2d75 100644
--- a/lib/smp_processor_id.c
+++ b/lib/smp_processor_id.c
@@ -22,7 +22,7 @@ notrace static unsigned int check_preemption_disabled(const char *what1,
 	 * Kernel threads bound to a single CPU can safely use
 	 * smp_processor_id():
 	 */
-	if (cpumask_equal(current->cpus_ptr, cpumask_of(this_cpu)))
+	if (current->nr_cpus_allowed == 1)
 		goto out;
 
 	/*
-- 
2.24.1