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]
Date:   Tue, 11 May 2021 16:12:14 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH tip/core/rcu 17/26] rcutorture: Delay-based false positives for RCU priority boosting tests

If an rcu_torture_boost() kthread determines that its grace period
has not yet ended, it invokes rcu_torture_boost_failed() which checks
whether enough time has elapsed for this to be considered a failure of
RCU priority boosting, and, if so, flags the error.

Unfortunately, that kthread might be preempted for some seconds between
the time that it checks the grace period and the time that it checks the
time.  This delay can result in a false positive, featuring a complaint
that a particular grace period has not ended, followed by a diagnostic
dump featuring a much later grace period.

This commit avoids these false positives by rechecking for the end of
the grace period after the time check.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/rcutorture.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 06d08f4f3e52..3defd0febe15 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -921,6 +921,10 @@ static bool rcu_torture_boost_failed(unsigned long gp_state, unsigned long start
 	static int dbg_done;
 
 	if (end - start > test_boost_duration * HZ - HZ / 2) {
+		// Recheck after checking time to avoid false positives.
+		smp_mb(); // Time check before grace-period check.
+		if (cur_ops->poll_gp_state(gp_state))
+			return false; // passed, though perhaps just barely
 		VERBOSE_TOROUT_STRING("rcu_torture_boost boosting failed");
 		n_rcu_torture_boost_failure++;
 		if (!xchg(&dbg_done, 1) && cur_ops->gp_kthread_dbg) {
@@ -929,10 +933,10 @@ static bool rcu_torture_boost_failed(unsigned long gp_state, unsigned long start
 			cur_ops->gp_kthread_dbg();
 		}
 
-		return true; /* failed */
+		return true; // failed
 	}
 
-	return false; /* passed */
+	return false; // passed
 }
 
 static int rcu_torture_boost(void *arg)
-- 
2.31.1.189.g2e36527f23

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ