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Subject[PATCH RFC tip/core/rcu 1/2] rcu: suppress RCU lockdep warnings during early boot
Date
RCU is used during very early boot, before RCU and lockdep have been
initialized. So make the underlying primitives (rcu_read_lock_held(),
rcu_read_lock_bh_held(), rcu_read_lock_sched_held(), and
rcu_dereference_check()) check for early boot via the rcu_scheduler_active
flag. This will suppress false positives.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
include/linux/rcupdate.h | 26 +++++++++++++++++---------
1 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index c843736..af51d5f 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -104,12 +104,14 @@ extern struct lockdep_map rcu_sched_lock_map;
* an RCU read-side critical section. In absence of CONFIG_PROVE_LOCKING,
* this assumes we are in an RCU read-side critical section unless it can
* prove otherwise.
+ *
+ * Check rcu_scheduler_active to prevent false positives during boot.
*/
static inline int rcu_read_lock_held(void)
{
- if (debug_locks)
- return lock_is_held(&rcu_lock_map);
- return 1;
+ if (!rcu_scheduler_active || !debug_locks)
+ return 1;
+ return lock_is_held(&rcu_lock_map);
}

/**
@@ -119,12 +121,14 @@ static inline int rcu_read_lock_held(void)
* an RCU-bh read-side critical section. In absence of CONFIG_PROVE_LOCKING,
* this assumes we are in an RCU-bh read-side critical section unless it can
* prove otherwise.
+ *
+ * Check rcu_scheduler_active to prevent false positives during boot.
*/
static inline int rcu_read_lock_bh_held(void)
{
- if (debug_locks)
- return lock_is_held(&rcu_bh_lock_map);
- return 1;
+ if (!rcu_scheduler_active || !debug_locks)
+ return 1;
+ return lock_is_held(&rcu_bh_lock_map);
}

/**
@@ -135,14 +139,18 @@ static inline int rcu_read_lock_bh_held(void)
* this assumes we are in an RCU-sched read-side critical section unless it
* can prove otherwise. Note that disabling of preemption (including
* disabling irqs) counts as an RCU-sched read-side critical section.
+ *
+ * Check rcu_scheduler_active to prevent false positives during boot.
*/
static inline int rcu_read_lock_sched_held(void)
{
int lockdep_opinion = 0;

+ if (!rcu_scheduler_active || !debug_locks)
+ return 1;
if (debug_locks)
lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
- return lockdep_opinion || preempt_count() != 0 || !rcu_scheduler_active;
+ return lockdep_opinion || preempt_count() != 0;
}

#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
@@ -166,7 +174,7 @@ static inline int rcu_read_lock_bh_held(void)

static inline int rcu_read_lock_sched_held(void)
{
- return preempt_count() != 0 || !rcu_scheduler_active;
+ return !rcu_scheduler_active || preempt_count() != 0;
}

#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
@@ -184,7 +192,7 @@ static inline int rcu_read_lock_sched_held(void)
*/
#define rcu_dereference_check(p, c) \
({ \
- if (debug_locks && !(c)) \
+ if (rcu_scheduler_active && debug_locks && !(c)) \
lockdep_rcu_dereference(__FILE__, __LINE__); \
rcu_dereference_raw(p); \
})
--
1.6.6


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