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Subject[PATCH 2/9] rcu: Add support for consolidated-RCU reader checking (v3)
Date
This patch adds support for checking RCU reader sections in list
traversal macros. Optionally, if the list macro is called under SRCU or
other lock/mutex protection, then appropriate lockdep expressions can be
passed to make the checks pass.

Existing list_for_each_entry_rcu() invocations don't need to pass the
optional fourth argument (cond) unless they are under some non-RCU
protection and needs to make lockdep check pass.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
include/linux/rculist.h | 28 ++++++++++++++++++++-----
include/linux/rcupdate.h | 7 +++++++
kernel/rcu/Kconfig.debug | 11 ++++++++++
kernel/rcu/update.c | 44 ++++++++++++++++++++++++----------------
4 files changed, 67 insertions(+), 23 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index e91ec9ddcd30..1048160625bb 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -40,6 +40,20 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
*/
#define list_next_rcu(list) (*((struct list_head __rcu **)(&(list)->next)))

+/*
+ * Check during list traversal that we are within an RCU reader
+ */
+
+#ifdef CONFIG_PROVE_RCU_LIST
+#define __list_check_rcu(dummy, cond, ...) \
+ ({ \
+ RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(), \
+ "RCU-list traversed in non-reader section!"); \
+ })
+#else
+#define __list_check_rcu(dummy, cond, ...) ({})
+#endif
+
/*
* Insert a new entry between two known consecutive entries.
*
@@ -343,14 +357,16 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
* @pos: the type * to use as a loop cursor.
* @head: the head for your list.
* @member: the name of the list_head within the struct.
+ * @cond: optional lockdep expression if called from non-RCU protection.
*
* This list-traversal primitive may safely run concurrently with
* the _rcu list-mutation primitives such as list_add_rcu()
* as long as the traversal is guarded by rcu_read_lock().
*/
-#define list_for_each_entry_rcu(pos, head, member) \
- for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
- &pos->member != (head); \
+#define list_for_each_entry_rcu(pos, head, member, cond...) \
+ for (__list_check_rcu(dummy, ## cond, 0), \
+ pos = list_entry_rcu((head)->next, typeof(*pos), member); \
+ &pos->member != (head); \
pos = list_entry_rcu(pos->member.next, typeof(*pos), member))

/**
@@ -616,13 +632,15 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
* @pos: the type * to use as a loop cursor.
* @head: the head for your list.
* @member: the name of the hlist_node within the struct.
+ * @cond: optional lockdep expression if called from non-RCU protection.
*
* This list-traversal primitive may safely run concurrently with
* the _rcu list-mutation primitives such as hlist_add_head_rcu()
* as long as the traversal is guarded by rcu_read_lock().
*/
-#define hlist_for_each_entry_rcu(pos, head, member) \
- for (pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
+#define hlist_for_each_entry_rcu(pos, head, member, cond...) \
+ for (__list_check_rcu(dummy, ## cond, 0), \
+ pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
typeof(*(pos)), member); \
pos; \
pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 8f7167478c1d..f3c29efdf19a 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -221,6 +221,7 @@ int debug_lockdep_rcu_enabled(void);
int rcu_read_lock_held(void);
int rcu_read_lock_bh_held(void);
int rcu_read_lock_sched_held(void);
+int rcu_read_lock_any_held(void);

#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

@@ -241,6 +242,12 @@ static inline int rcu_read_lock_sched_held(void)
{
return !preemptible();
}
+
+static inline int rcu_read_lock_any_held(void)
+{
+ return !preemptible();
+}
+
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

#ifdef CONFIG_PROVE_RCU
diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 5ec3ea4028e2..7fbd21dbfcd0 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -8,6 +8,17 @@ menu "RCU Debugging"
config PROVE_RCU
def_bool PROVE_LOCKING

+config PROVE_RCU_LIST
+ bool "RCU list lockdep debugging"
+ depends on PROVE_RCU
+ default n
+ help
+ Enable RCU lockdep checking for list usages. By default it is
+ turned off since there are several list RCU users that still
+ need to be converted to pass a lockdep expression. To prevent
+ false-positive splats, we keep it default disabled but once all
+ users are converted, we can remove this config option.
+
config TORTURE_TEST
tristate
default n
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 9dd5aeef6e70..b7a4e3b5fa98 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -91,14 +91,18 @@ module_param(rcu_normal_after_boot, int, 0);
* Similarly, we avoid claiming an SRCU read lock held if the current
* CPU is offline.
*/
+#define rcu_read_lock_held_common() \
+ if (!debug_lockdep_rcu_enabled()) \
+ return 1; \
+ if (!rcu_is_watching()) \
+ return 0; \
+ if (!rcu_lockdep_current_cpu_online()) \
+ return 0;
+
int rcu_read_lock_sched_held(void)
{
- if (!debug_lockdep_rcu_enabled())
- return 1;
- if (!rcu_is_watching())
- return 0;
- if (!rcu_lockdep_current_cpu_online())
- return 0;
+ rcu_read_lock_held_common();
+
return lock_is_held(&rcu_sched_lock_map) || !preemptible();
}
EXPORT_SYMBOL(rcu_read_lock_sched_held);
@@ -257,12 +261,8 @@ NOKPROBE_SYMBOL(debug_lockdep_rcu_enabled);
*/
int rcu_read_lock_held(void)
{
- if (!debug_lockdep_rcu_enabled())
- return 1;
- if (!rcu_is_watching())
- return 0;
- if (!rcu_lockdep_current_cpu_online())
- return 0;
+ rcu_read_lock_held_common();
+
return lock_is_held(&rcu_lock_map);
}
EXPORT_SYMBOL_GPL(rcu_read_lock_held);
@@ -284,16 +284,24 @@ EXPORT_SYMBOL_GPL(rcu_read_lock_held);
*/
int rcu_read_lock_bh_held(void)
{
- if (!debug_lockdep_rcu_enabled())
- return 1;
- if (!rcu_is_watching())
- return 0;
- if (!rcu_lockdep_current_cpu_online())
- return 0;
+ rcu_read_lock_held_common();
+
return in_softirq() || irqs_disabled();
}
EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);

+int rcu_read_lock_any_held(void)
+{
+ rcu_read_lock_held_common();
+
+ if (lock_is_held(&rcu_lock_map) ||
+ lock_is_held(&rcu_bh_lock_map) ||
+ lock_is_held(&rcu_sched_lock_map))
+ return 1;
+ return !preemptible();
+}
+EXPORT_SYMBOL_GPL(rcu_read_lock_any_held);
+
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

/**
--
2.22.0.510.g264f2c817a-goog
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