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From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     rcu@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, kernel-team@fb.com,
        rostedt@goodmis.org, "Paul E. McKenney" <paulmck@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        John Ogness <john.ogness@linutronix.de>,
        Petr Mladek <pmladek@suse.com>
Subject: [PATCH RFC v2 rcu 4/8] srcu: Check for consistent global per-srcu_struct NMI safety
Date:   Thu, 29 Sep 2022 11:07:27 -0700
Message-Id: <20220929180731.2875722-4-paulmck@kernel.org>
In-Reply-To: <20220929180714.GA2874192@paulmck-ThinkPad-P17-Gen-1>
References: <20220929180714.GA2874192@paulmck-ThinkPad-P17-Gen-1>
MIME-Version: 1.0
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Precedence: bulk

This commit adds runtime checks to verify that a given srcu_struct uses
consistent NMI-safe (or not) read-side primitives globally, but based
on the per-CPU data.  These global checks are made by the grace-period
code that must scan the srcu_data structures anyway, and are done only
in kernels built with CONFIG_PROVE_RCU=y.

Link: https://lore.kernel.org/all/20220910221947.171557773@linutronix.de/

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>
---
 kernel/rcu/srcutree.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 09a11f2c2042..5772b8659c89 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -429,13 +429,18 @@ static unsigned long srcu_readers_lock_idx(struct srcu_struct *ssp, int idx)
 static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx)
 {
 	int cpu;
+	unsigned long mask = 0;
 	unsigned long sum = 0;
 
 	for_each_possible_cpu(cpu) {
 		struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
 
 		sum += atomic_long_read(&cpuc->srcu_unlock_count[idx]);
+		if (IS_ENABLED(CONFIG_PROVE_RCU))
+			mask = mask | READ_ONCE(cpuc->srcu_nmi_safety);
 	}
+	WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask >> 1)),
+		  "Mixed NMI-safe readers for srcu_struct at %ps.\n", ssp);
 	return sum;
 }
 
-- 
2.31.1.189.g2e36527f23