linux-kernel - [PATCH 11/16] rcu/nocb: Allow de-offloading rdp leader

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: <20210128171222.131380-12-frederic@kernel.org>
Date:   Thu, 28 Jan 2021 18:12:17 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Paul E . McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Josh Triplett <josh@...htriplett.org>,
        Stable <stable@...r.kernel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: [PATCH 11/16] rcu/nocb: Allow de-offloading rdp leader

The only thing that prevented an rdp leader from being de-offloaded was
the nocb_bypass_timer that used to lock the nocb_lock of the rdp leader.

If an rdp gets de-offloaded, it will subtely ignore rcu_nocb_lock()
calls and do its job in the timer unsafely. Worse yet: if it gets
re-offloaded in the middle of the timer, rcu_nocb_unlock() would try to
unlock, leaving it imbalanced.

Now that the nocb_bypass_timer doesn't use the nocb_lock anymore, we can
safely allow rdp leader to be de-offloaded.

Reported-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Josh Triplett <josh@...htriplett.org>
Cc: Lai Jiangshan <jiangshanlai@...il.com>
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: Neeraj Upadhyay <neeraju@...eaurora.org>
Cc: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/rcu/tree_plugin.h | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 28ace1ae83d6..dae892ac570a 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2481,10 +2481,6 @@ int rcu_nocb_cpu_deoffload(int cpu)
 	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
 	int ret = 0;
 
-	if (rdp == rdp->nocb_gp_rdp) {
-		pr_info("Can't deoffload an rdp GP leader (yet)\n");
-		return -EINVAL;
-	}
 	mutex_lock(&rcu_state.barrier_mutex);
 	cpus_read_lock();
 	if (rcu_rdp_is_offloaded(rdp)) {
-- 
2.25.1