1 files changed, 74 insertions, 13 deletions

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 58971e891f48..e1b005918bbb 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 +83,32 @@ 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.
+ *
+ * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
+ * and while lockdep is disabled.
+ *
+ * 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_lockdep_rcu_enabled())
+                return 1;
+
+        return lock_is_held(&sp->dep_map);
 }
 
 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
@@ -145,12 +158,17 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp)
  * one way to indirectly wait on an SRCU grace period is to acquire
  * a mutex that is held elsewhere while calling synchronize_srcu() or
  * synchronize_srcu_expedited().
+ *
+ * Note that srcu_read_lock() and the matching srcu_read_unlock() must
+ * occur in the same context, for example, it is illegal to invoke
+ * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
+ * was invoked in process context.
  */
 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;
 }
 
@@ -164,8 +182,51 @@ 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);
+}
+
+/**
+ * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
+ * @sp: srcu_struct in which to register the new reader.
+ *
+ * Enter an SRCU read-side critical section.  Similar to srcu_read_lock(),
+ * but avoids the RCU-lockdep checking.  This means that it is legal to
+ * use srcu_read_lock_raw() in one context, for example, in an exception
+ * handler, and then have the matching srcu_read_unlock_raw() in another
+ * context, for example in the task that took the exception.
+ *
+ * However, the entire SRCU read-side critical section must reside within a
+ * single task.  For example, beware of using srcu_read_lock_raw() in
+ * a device interrupt handler and srcu_read_unlock() in the interrupted
+ * task:  This will not work if interrupts are threaded.
+ */
+static inline int srcu_read_lock_raw(struct srcu_struct *sp)
+{
+        unsigned long flags;
+        int ret;
+
+        local_irq_save(flags);
+        ret =  __srcu_read_lock(sp);
+        local_irq_restore(flags);
+        return ret;
+}
+
+/**
+ * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
+ * @sp: srcu_struct in which to unregister the old reader.
+ * @idx: return value from corresponding srcu_read_lock_raw().
+ *
+ * Exit an SRCU read-side critical section without lockdep-RCU checking.
+ * See srcu_read_lock_raw() for more details.
+ */
+static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
+{
+        unsigned long flags;
+
+        local_irq_save(flags);
         __srcu_read_unlock(sp, idx);
+        local_irq_restore(flags);
 }
 
 #endif