Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [PATCH 05/11] rcu: Warn when srcu_read_lock() is used in an extended quiescent state | Date | Fri, 7 Oct 2011 18:22:04 +0200 |
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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Catch SRCU up to the other variants of RCU by making PROVE_RCU complain if either srcu_read_lock() or srcu_read_lock_held() are used from within RCU-idle mode.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> --- include/linux/srcu.h | 35 ++++++++++++++++++++++------------- 1 files changed, 22 insertions(+), 13 deletions(-)
diff --git a/include/linux/srcu.h b/include/linux/srcu.h index 58971e8..553c003 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -28,6 +28,7 @@ #define _LINUX_SRCU_H #include <linux/mutex.h> +#include <linux/rcupdate.h> struct srcu_struct_array { int c[2]; @@ -60,18 +61,10 @@ int __init_srcu_struct(struct srcu_struct *sp, const char *name, __init_srcu_struct((sp), #sp, &__srcu_key); \ }) -# define srcu_read_acquire(sp) \ - lock_acquire(&(sp)->dep_map, 0, 0, 2, 1, NULL, _THIS_IP_) -# define srcu_read_release(sp) \ - lock_release(&(sp)->dep_map, 1, _THIS_IP_) - #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ int init_srcu_struct(struct srcu_struct *sp); -# define srcu_read_acquire(sp) do { } while (0) -# define srcu_read_release(sp) do { } while (0) - #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ void cleanup_srcu_struct(struct srcu_struct *sp); @@ -90,12 +83,28 @@ long srcu_batches_completed(struct srcu_struct *sp); * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, * this assumes we are in an SRCU read-side critical section unless it can * prove otherwise. + * + * Note that if the CPU is in the idle loop from an RCU point of view + * (ie: that we are in the section between rcu_idle_enter() and rcu_idle_exit()) + * then srcu_read_lock_held() returns false even if the CPU did an srcu_read_lock(). + * The reason for this is that RCU ignores CPUs that are in such a section, + * considering these as in extended quiescent state, so such a CPU is effectively + * never in an RCU read-side critical section regardless of what RCU primitives it + * invokes. This state of affairs is required --- we need to keep an RCU-free + * window in idle where the CPU may possibly enter into low power mode. This way + * we can notice an extended quiescent state to other CPUs that started a grace + * period. Otherwise we would delay any grace period as long as we run in the + * idle task. */ static inline int srcu_read_lock_held(struct srcu_struct *sp) { - if (debug_locks) - return lock_is_held(&sp->dep_map); - return 1; + if (rcu_is_cpu_idle()) + return 0; + + if (!debug_locks) + return 1; + + return lock_is_held(&sp->dep_map); } #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ @@ -150,7 +159,7 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp) { int retval = __srcu_read_lock(sp); - srcu_read_acquire(sp); + rcu_lock_acquire(&(sp)->dep_map); return retval; } @@ -164,7 +173,7 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp) static inline void srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp) { - srcu_read_release(sp); + rcu_lock_release(&(sp)->dep_map); __srcu_read_unlock(sp, idx); } -- 1.7.5.4
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