[PATCH RFC v2 rcu 4/8] srcu: Check for consistent global per-srcu_struct NMI safety

Paul E. McKenney
2022-09-29T18:07:39Z

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