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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

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* '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
This commit is contained in:
Linus Torvalds 2010-04-19 08:35:47 -07:00
commit 85341c6136
6 changed files with 120 additions and 30 deletions
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65
include/linux/rcupdate.h
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@ -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 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().
* 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));
*
* 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) \
({ \
@ -209,12 +224,44 @@ 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.
*