srcu: Check for consistent global per-srcu_struct NMI safety

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>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 3057586..87ae6f5 100644 (file)
--- 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;
 }