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Subject[RFC][PATCH 3/5] rcusync: Add the CONFIG_PROVE_RCU checks
From: Oleg Nesterov <oleg@redhat.com>

It would be nice to validate that the caller of rcu_sync_is_idle()
holds the corresponding type of RCU read-side lock. Add the new
rcu_sync_ops->held() method and change rcu_sync_is_idle() to
WARN() if it returns false.

This obviously penalizes the readers (fast-path), but only if
CONFIG_PROVE_RCU.

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Suggested-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/rcusync.h | 6 ++++++
kernel/rcu/sync.c | 21 +++++++++++++++++++++
2 files changed, 27 insertions(+)

--- a/include/linux/rcusync.h
+++ b/include/linux/rcusync.h
@@ -17,9 +17,15 @@ struct rcu_sync_struct {
enum rcu_sync_type gp_type;
};

+extern bool __rcu_sync_is_idle(struct rcu_sync_struct *);
+
static inline bool rcu_sync_is_idle(struct rcu_sync_struct *rss)
{
+#ifdef CONFIG_PROVE_RCU
+ return __rcu_sync_is_idle(rss);
+#else
return !rss->gp_state; /* GP_IDLE */
+#endif
}

extern void rcu_sync_init(struct rcu_sync_struct *, enum rcu_sync_type);
--- a/kernel/rcu/sync.c
+++ b/kernel/rcu/sync.c
@@ -1,21 +1,33 @@
#include <linux/rcusync.h>
#include <linux/sched.h>

+#ifdef CONFIG_PROVE_RCU
+#define __INIT_HELD(func) .held = func,
+#else
+#define __INIT_HELD(func)
+#endif
+
static const struct {
void (*sync)(void);
void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
+#ifdef CONFIG_PROVE_RCU
+ int (*held)(void);
+#endif
} gp_ops[] = {
[RCU_SYNC] = {
.sync = synchronize_rcu,
.call = call_rcu,
+ __INIT_HELD(rcu_read_lock_held)
},
[RCU_SCHED_SYNC] = {
.sync = synchronize_sched,
.call = call_rcu_sched,
+ __INIT_HELD(rcu_read_lock_sched_held)
},
[RCU_BH_SYNC] = {
.sync = synchronize_rcu_bh,
.call = call_rcu_bh,
+ __INIT_HELD(rcu_read_lock_bh_held)
},
};

@@ -24,6 +36,15 @@ enum { CB_IDLE = 0, CB_PENDING, CB_REPLA

#define rss_lock gp_wait.lock

+#ifdef CONFIG_PROVE_RCU
+bool __rcu_sync_is_idle(struct rcu_sync_struct *rss)
+{
+ WARN_ON(!gp_ops[rss->gp_type].held());
+ return rss->gp_state == GP_IDLE;
+}
+EXPORT_SYMBOL_GPL(__rcu_sync_is_idle);
+#endif
+
void rcu_sync_init(struct rcu_sync_struct *rss, enum rcu_sync_type type)
{
memset(rss, 0, sizeof(*rss));



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