Messages in this thread Patch in this message | | | From | Boqun Feng <> | Subject | [RFC v2 6/6] RCU: Track rcu_dereference() in RCU read-side critical section | Date | Tue, 16 Feb 2016 13:57:45 +0800 |
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The variables protected by an RCU read-side critical section are sometimes hard to figure out, especially when the critical section is long or has some function calls in it. However, figuring out which variable a RCU read-side critical section protects could save us a lot of time for code reviewing, bug fixing or performance tuning.
This patch therefore uses the LOCKED_ACCESS to collect the information of relationship between rcu_dereference*() and rcu_read_lock*() by doing:
Step 0: define a locked_access_class for RCU.
Step 1: set the content of rcu_*_lock_key and __srcu_key to the address of the locked_access_class for RCU.
Step 2: add locked_access_point() in __rcu_dereference_check()
After that we can figure out not only in which RCU read-side critical section but also after which rcu_read_lock*() called an rcu_dereference*() is called.
This feature is controlled by a config option RCU_LOCKED_ACCESS.
Also clean up the initialization code of lockdep_maps for different flavors of RCU a little bit.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com> --- include/linux/rcupdate.h | 12 ++++++++++++ include/linux/srcu.h | 2 +- kernel/locking/lockdep.c | 3 +++ kernel/rcu/update.c | 25 +++++++++++-------------- lib/Kconfig.debug | 12 ++++++++++++ 5 files changed, 39 insertions(+), 15 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 14e6f47..7ca22c1 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -610,6 +610,17 @@ static inline void rcu_preempt_sleep_check(void) #define rcu_dereference_sparse(p, space) #endif /* #else #ifdef __CHECKER__ */ +#ifdef CONFIG_RCU_LOCKED_ACCESS +extern struct locked_access_class rcu_laclass; +#define STATIC_DEFINE_RCU_LOCK_CLASS_KEY(name) \ + static struct lock_class_key name = { .laclass = &rcu_laclass } +#define rcu_dereference_access() \ + locked_access_point(&rcu_laclass, LOCKED_ACCESS_TYPE_READ) +#else /* #ifdef CONFIG_LOCKED_ACCESS */ +#define rcu_dereference_access() +#define STATIC_DEFINE_RCU_LOCK_CLASS_KEY(name) \ + static struct lock_class_key name +#endif /* #else #ifdef CONFIG_LOCKED_ACCESS */ #define __rcu_access_pointer(p, space) \ ({ \ typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \ @@ -622,6 +633,7 @@ static inline void rcu_preempt_sleep_check(void) typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \ RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ rcu_dereference_sparse(p, space); \ + rcu_dereference_access(); \ ((typeof(*p) __force __kernel *)(________p1)); \ }) #define __rcu_dereference_protected(p, c, space) \ diff --git a/include/linux/srcu.h b/include/linux/srcu.h index f5f80c5..ba4bcbe 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -69,7 +69,7 @@ int __init_srcu_struct(struct srcu_struct *sp, const char *name, #define init_srcu_struct(sp) \ ({ \ - static struct lock_class_key __srcu_key; \ + STATIC_DEFINE_RCU_LOCK_CLASS_KEY(__srcu_key); \ \ __init_srcu_struct((sp), #sp, &__srcu_key); \ }) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 4094757..c6c25c5 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -4616,5 +4616,8 @@ void locked_access(struct locked_access_class *laclass, correlate_locked_access(laclass, acqchain, loc, type); } EXPORT_SYMBOL(locked_access); +#ifdef CONFIG_RCU_LOCKED_ACCESS +DEFINE_LACLASS(rcu); +#endif #endif /* CONFIG_LOCKED_ACCESS */ diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 76b94e1..ecb29aa 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -235,20 +235,17 @@ EXPORT_SYMBOL_GPL(__rcu_read_unlock); #endif /* #ifdef CONFIG_PREEMPT_RCU */ #ifdef CONFIG_DEBUG_LOCK_ALLOC -static struct lock_class_key rcu_lock_key; -struct lockdep_map rcu_lock_map = - STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); -EXPORT_SYMBOL_GPL(rcu_lock_map); - -static struct lock_class_key rcu_bh_lock_key; -struct lockdep_map rcu_bh_lock_map = - STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key); -EXPORT_SYMBOL_GPL(rcu_bh_lock_map); - -static struct lock_class_key rcu_sched_lock_key; -struct lockdep_map rcu_sched_lock_map = - STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key); -EXPORT_SYMBOL_GPL(rcu_sched_lock_map); + +#define DEFINE_RCU_LOCKDEP_MAP(flavor) \ + STATIC_DEFINE_RCU_LOCK_CLASS_KEY(rcu##flavor##_lock_key); \ + struct lockdep_map rcu##flavor##_lock_map = \ + STATIC_LOCKDEP_MAP_INIT("rcu" #flavor "_read_lock", \ + &rcu##flavor##_lock_key); \ + EXPORT_SYMBOL_GPL(rcu##flavor##_lock_map) + +DEFINE_RCU_LOCKDEP_MAP(); +DEFINE_RCU_LOCKDEP_MAP(_bh); +DEFINE_RCU_LOCKDEP_MAP(_sched); static struct lock_class_key rcu_callback_key; struct lockdep_map rcu_callback_map = diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 178f288..b6003d4 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1410,6 +1410,18 @@ config RCU_EQS_DEBUG Say N here if you need ultimate kernel/user switch latencies Say Y if you are unsure +config RCU_LOCKED_ACCESS + bool "Track data access in RCU read-side critical sections" + depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT + select LOCKED_ACCESS + default n + help + Track data acces in RCU read-side critical sections, + by doing so, one can examine which rcu_dereference() and its + friends are called in which RCU read-side critical sections, + and even more detailed, after which rcu_read_lock() and + its friends are called. + endmenu # "RCU Debugging" config DEBUG_BLOCK_EXT_DEVT -- 2.7.1
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