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authorLinus Torvalds <torvalds@linux-foundation.org>2010-04-19 08:35:47 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-04-19 08:35:47 -0700
commit85341c61361cc45a9cc0e11c01e8f4479ef460ac (patch)
tree8d5e8e98aaef7f77f9749d851dd409ac356f0258 /include
parent375db4810b27306ea400ab39d3d6f7a063ac9ff6 (diff)
parentbc293d62b26ec590afc90a9e0a31c45d355b7bd8 (diff)
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Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: rcu: Make RCU lockdep check the lockdep_recursion variable rcu: Update docs for rcu_access_pointer and rcu_dereference_protected rcu: Better explain the condition parameter of rcu_dereference_check() rcu: Add rcu_access_pointer and rcu_dereference_protected
Diffstat (limited to 'include')
-rw-r--r--include/linux/rcupdate.h65
1 files changed, 56 insertions, 9 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 872a98e13d6..07db2feb857 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -101,10 +101,7 @@ extern struct lockdep_map rcu_sched_lock_map;
# define rcu_read_release_sched() \
lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
-static inline int debug_lockdep_rcu_enabled(void)
-{
- return likely(rcu_scheduler_active && debug_locks);
-}
+extern int debug_lockdep_rcu_enabled(void);
/**
* rcu_read_lock_held - might we be in RCU read-side critical section?
@@ -195,12 +192,30 @@ static inline int rcu_read_lock_sched_held(void)
/**
* rcu_dereference_check - rcu_dereference with debug checking
+ * @p: The pointer to read, prior to dereferencing
+ * @c: The conditions under which the dereference will take place
+ *
+ * Do an rcu_dereference(), but check that the conditions under which the
+ * dereference will take place are correct. Typically the conditions indicate
+ * the various locking conditions that should be held at that point. The check
+ * should return true if the conditions are satisfied.
+ *
+ * For example:
+ *
+ * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
+ * lockdep_is_held(&foo->lock));
*
- * Do an rcu_dereference(), but check that the context is correct.
- * For example, rcu_dereference_check(gp, rcu_read_lock_held()) to
- * ensure that the rcu_dereference_check() executes within an RCU
- * read-side critical section. It is also possible to check for
- * locks being held, for example, by using lockdep_is_held().
+ * could be used to indicate to lockdep that foo->bar may only be dereferenced
+ * if either the RCU read lock is held, or that the lock required to replace
+ * the bar struct at foo->bar is held.
+ *
+ * Note that the list of conditions may also include indications of when a lock
+ * need not be held, for example during initialisation or destruction of the
+ * target struct:
+ *
+ * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() ||
+ * lockdep_is_held(&foo->lock) ||
+ * atomic_read(&foo->usage) == 0);
*/
#define rcu_dereference_check(p, c) \
({ \
@@ -209,13 +224,45 @@ static inline int rcu_read_lock_sched_held(void)
rcu_dereference_raw(p); \
})
+/**
+ * rcu_dereference_protected - fetch RCU pointer when updates prevented
+ *
+ * Return the value of the specified RCU-protected pointer, but omit
+ * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
+ * is useful in cases where update-side locks prevent the value of the
+ * pointer from changing. Please note that this primitive does -not-
+ * prevent the compiler from repeating this reference or combining it
+ * with other references, so it should not be used without protection
+ * of appropriate locks.
+ */
+#define rcu_dereference_protected(p, c) \
+ ({ \
+ if (debug_lockdep_rcu_enabled() && !(c)) \
+ lockdep_rcu_dereference(__FILE__, __LINE__); \
+ (p); \
+ })
+
#else /* #ifdef CONFIG_PROVE_RCU */
#define rcu_dereference_check(p, c) rcu_dereference_raw(p)
+#define rcu_dereference_protected(p, c) (p)
#endif /* #else #ifdef CONFIG_PROVE_RCU */
/**
+ * rcu_access_pointer - fetch RCU pointer with no dereferencing
+ *
+ * Return the value of the specified RCU-protected pointer, but omit the
+ * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
+ * when the value of this pointer is accessed, but the pointer is not
+ * dereferenced, for example, when testing an RCU-protected pointer against
+ * NULL. This may also be used in cases where update-side locks prevent
+ * the value of the pointer from changing, but rcu_dereference_protected()
+ * is a lighter-weight primitive for this use case.
+ */
+#define rcu_access_pointer(p) ACCESS_ONCE(p)
+
+/**
* rcu_read_lock - mark the beginning of an RCU read-side critical section.
*
* When synchronize_rcu() is invoked on one CPU while other CPUs