/*
* Read-Copy Update mechanism for mutual exclusion
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright IBM Corporation, 2001
*
* Author: Dipankar Sarma <dipankar@in.ibm.com>
*
* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
* Papers:
* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
*
* For detailed explanation of Read-Copy Update mechanism see -
* http://lse.sourceforge.net/locking/rcupdate.html
*
*/
#ifndef __LINUX_RCUPDATE_H
#define __LINUX_RCUPDATE_H
#include <linux/types.h>
#include <linux/cache.h>
#include <linux/spinlock.h>
#include <linux/threads.h>
#include <linux/cpumask.h>
#include <linux/seqlock.h>
#include <linux/lockdep.h>
#include <linux/completion.h>
#include <linux/debugobjects.h>
#include <linux/compiler.h>
#ifdef CONFIG_RCU_TORTURE_TEST
extern int rcutorture_runnable; /* for sysctl */
#endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
extern void rcutorture_record_test_transition(void);
extern void rcutorture_record_progress(unsigned long vernum);
extern void do_trace_rcu_torture_read(char *rcutorturename,
struct rcu_head *rhp);
#else
static inline void rcutorture_record_test_transition(void)
{
}
static inline void rcutorture_record_progress(unsigned long vernum)
{
}
#ifdef CONFIG_RCU_TRACE
extern void do_trace_rcu_torture_read(char *rcutorturename,
struct rcu_head *rhp);
#else
#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
#endif
#endif
#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b))
#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b))
#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
/* Exported common interfaces */
#ifdef CONFIG_PREEMPT_RCU
/**
* call_rcu() - Queue an RCU callback for invocation after a grace period.
* @head: structure to be used for queueing the RCU updates.
* @func: actual callback function to be invoked after the grace period
*
* The callback function will be invoked some time after a full grace
* period elapses, in other words after all pre-existing RCU read-side
* critical sections have completed. However, the callback function
* might well execute concurrently with RCU read-side critical sections
* that started after call_rcu() was invoked. RCU read-side critical
* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
* and may be nested.
*/
extern void call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *head));
#else /* #ifdef CONFIG_PREEMPT_RCU */
/* In classic RCU, call_rcu() is just call_rcu_sched(). */
#define call_rcu call_rcu_sched
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
/**
* call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
* @head: structure to be used for queueing the RCU updates.
* @func: actual callback function to be invoked after the grace period
*
* The callback function will be invoked some time after a full grace
* period elapses, in other words after all currently executing RCU
* read-side critical sections have completed. call_rcu_bh() assumes
* that the read-side critical sections end on completion of a softirq
* handler. This means that read-side critical sections in process
* context must not be interrupted by softirqs. This interface is to be
* used when most of the read-side critical sections are in softirq context.
* RCU read-side critical sections are delimited by :
* - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
* OR
* - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
* These may be nested.
*/
extern void call_rcu_bh(struct rcu_head *head,
void (*func)(struct rcu_head *head));
/**
* call_rcu_sched() - Queue an RCU for invocation after sched grace period.
* @head: structure to be used for queueing the RCU updates.
* @func: actual callback function to be invoked after the grace period
*
* The callback function will be invoked some time after a full grace
* period elapses, in other words after all currently executing RCU
* read-side critical sections have completed. call_rcu_sched() assumes
* that the read-side critical sections end on enabling of preemption
* or on voluntary preemption.
* RCU read-side critical sections are delimited by :
* - rcu_read_lock_sched() and rcu_read_unlock_sched(),
* OR
* anything that disables preemption.
* These may be nested.
*/
extern void call_rcu_sched(struct rcu_head *head,
void (*func)(struct rcu_head *rcu));
extern void synchronize_sched(void);
#ifdef CONFIG_PREEMPT_RCU
extern void __rcu_read_lock(void);
extern void __rcu_read_unlock(void);
void synchronize_rcu(void);
/*
* Defined as a macro as it is a very low level header included from
* areas that don't even know about current. This gives the rcu_read_lock()
* nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
* types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
*/
#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
#else /* #ifdef CONFIG_PREEMPT_RCU */
static inline void __rcu_read_lock(void)
{
preempt_disable();
}
static inline void __rcu_read_unlock(void)
{
preempt_enable();
}
static inline void synchronize_rcu(void)
{
synchronize_sched();
}
static inline int rcu_preempt_depth(void)
{
return 0;
}
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
/* Internal to kernel */
extern void rcu_sched_qs(int cpu);
extern void rcu_bh_qs(int cpu);
extern void rcu_check_callbacks(int cpu, int user);
struct notifier_block;
extern void rcu_idle_enter(void);
extern void rcu_idle_exit(void);
extern void rcu_irq_enter(void);
extern void rcu_irq_exit(void);
/*
* Infrastructure to implement the synchronize_() primitives in
* TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
*/
typedef void call_rcu_func_t(struct rcu_head *head,
void (*func)(struct rcu_head *head));
void wait_rcu_gp(call_rcu_func_t crf);
#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
#include <linux/rcutree.h>
#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
#include <linux/rcutiny.h>
#else
#error "Unknown RCU implementation specified to kernel configuration"
#endif
/*
* init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
* initialization and destruction of rcu_head on the stack. rcu_head structures
* allocated dynamically in the heap or defined statically don't need any
* initialization.
*/
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
extern void init_rcu_head_on_stack(struct rcu_head *head);
extern void destroy_rcu_head_on_stack(struct rcu_head *head);
#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
static inline void init_rcu_head_on_stack(struct rcu_head *head)
{
}
static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
{
}
#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
bool rcu_lockdep_current_cpu_online(void);
#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
static inline bool rcu_lockdep_current_cpu_online(void)
{
return 1;
}
#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
#ifdef CONFIG_PROVE_RCU
extern int rcu_is_cpu_idle(void);
#else /* !CONFIG_PROVE_RCU */
static inline int rcu_is_cpu_idle(void)
{
return 0;
}
#endif /* else !CONFIG_PROVE_RCU */
static inline void rcu_lock_acquire(struct lockdep_map *map)
{
lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_);
}
static inline void rcu_lock_release(struct lockdep_map *map)
{
lock_release(map, 1, _THIS_IP_);
}
extern struct lockdep_map rcu_lock_map;
extern struct lockdep_map rcu_bh_lock_map;
extern struct lockdep_map rcu_sched_lock_map;
extern int debug_lockdep_rcu_enabled(void);
/**
* rcu_read_lock_held() - might we be in RCU read-side critical section?
*
* If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
* read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
* this assumes we are in an RCU read-side critical section unless it can
* prove otherwise. This is useful for debug checks in functions that
* require that they be called within an RCU read-side critical section.
*
* Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
* and while lockdep is disabled.
*
* Note that rcu_read_lock() and the matching rcu_read_unlock() must
* occur in the same context, for example, it is illegal to invoke
* rcu_read_unlock() in process context if the matching rcu_read_lock()
* was invoked from within an irq handler.
*
* Note that rcu_read_lock() is disallowed if the CPU is either idle or
* offline from an RCU perspective, so check for those as well.
*/
static inline int rcu_read_lock_held(void)
{
if (!debug_lockdep_rcu_enabled())
return 1;
if (rcu_is_cpu_idle())
return 0;
if (!rcu_lockdep_current_cpu_online())
return 0;
return lock_is_held(&rcu_lock_map);
}
/*
* rcu_read_lock_bh_held() is defined out of line to avoid #include-file
* hell.
*/
extern int rcu_read_lock_bh_held(void);
/**
* rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
*
* If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
* RCU-sched read-side critical section. In absence of
* CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
* critical section unless it can prove otherwise. Note that disabling
* of preemption (including disabling irqs) counts as an RCU-sched
* read-side critical section. This is useful for debug checks in functions
* that required that they be called within an RCU-sched read-side
* critical section.
*
* Check 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 rcu_read_lock_held() returns false even if the CPU
* did an rcu_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.
*
* Similarly, we avoid claiming an SRCU read lock held if the current
* CPU is offline.
*/
#ifdef CONFIG_PREEMPT_COUNT
static inline int rcu_read_lock_sched_held(void)
{
int lockdep_opinion = 0;
if (!debug_lockdep_rcu_enabled())
return 1;
if (rcu_is_cpu_idle())
return 0;
if (!rcu_lockdep_current_cpu_online())
return 0;
if (debug_locks)
lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
}
#else /* #ifdef CONFIG_PREEMPT_COUNT */
static inline int rcu_read_lock_sched_held(void)
{
return 1;
}
#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
# define rcu_lock_acquire(a) do { } while (0)
# define rcu_lock_release(a) do { } while (0)
static inline int rcu_read_lock_held(void)
{
return 1;
}
static inline int rcu_read_lock_bh_held(void)
{
return 1;
}
#ifdef CONFIG_PREEMPT_COUNT
static inline int rcu_read_lock_sched_held(void)
{
return preempt_count() != 0 || irqs_disabled();
}
#else /* #ifdef CONFIG_PREEMPT_COUNT */
static inline int rcu_read_lock_sched_held(void)
{
return 1;
}
#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
#ifdef CONFIG_PROVE_RCU
extern int rcu_my_thread_group_empty(void);
/**
* rcu_lockdep_assert - emit lockdep splat if specified condition not met
* @c: condition to check
* @s: informative message
*/
#define rcu_lockdep_assert(c, s) \
do { \
static bool __warned; \
if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
__warned = true; \
lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
} \
} while (0)
#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
static inline void rcu_preempt_sleep_check(void)
{
rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
"Illegal context switch in RCU read-side "
"critical section");
}
#else /* #ifdef CONFIG_PROVE_RCU */
static inline void rcu_preempt_sleep_check(void)
{
}
#endif /* #else #ifdef CONFIG_PROVE_RCU */
#define rcu_sleep_check() \
do { \
rcu_preempt_sleep_check(); \
rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \
"Illegal context switch in RCU-bh" \
" read-side critical section"); \
rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \
"Illegal context switch in RCU-sched"\
" read-side critical section"); \
} while (0)
#else /* #ifdef CONFIG_PROVE_RCU */
#define rcu_lockdep_assert(c, s) do { } while (0)
#define rcu_sleep_check() do { } while (0)
#endif /* #else #ifdef CONFIG_PROVE_RCU */
/*
* Helper functions for rcu_dereference_check(), rcu_dereference_protected()
* and rcu_assign_pointer(). Some of these could be folded into their
* callers, but they are left separate in order to ease introduction of
* multiple flavors of pointers to match the multiple flavors of RCU
* (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
* the future.
*/
#ifdef __CHECKER__
#define rcu_dereference_sparse(p, space) \
((void)(((typeof(*p) space *)p) == p))
#else /* #ifdef __CHECKER__ */
#define rcu_dereference_sparse(p, space)
#endif /* #else #ifdef __CHECKER__ */
#define __rcu_access_pointer(p, space) \
({ \
typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
rcu_dereference_sparse(p, space); \
((typeof(*p) __force __kernel *)(_________p1)); \
})
#define __rcu_dereference_check(p, c, space) \
({ \
typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
" usage"); \
rcu_dereference_sparse(p, space); \
smp_read_barrier_depends(); \
((typeof(*p) __force __kernel *)(_________p1)); \
})
#define __rcu_dereference_protected(p, c, space) \
({ \
rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
" usage"); \
rcu_dereference_sparse(p, space); \
((typeof(*p) __force __kernel *)(p)); \
})
#define __rcu_access_index(p, space) \
({ \
typeof(p) _________p1 = ACCESS_ONCE(p); \
rcu_dereference_sparse(p, space); \
(_________p1); \
})
#define __rcu_dereference_index_check(p, c) \
({ \
typeof(p) _________p1 = ACCESS_ONCE(p); \
rcu_lockdep_assert(c, \
"suspicious rcu_dereference_index_check()" \
" usage"); \
smp_read_barrier_depends(); \
(_________p1); \
})
#define __rcu_assign_pointer(p, v, space) \
({ \
smp_wmb(); \
(p) = (typeof(*v) __force space *)(v); \
})
/**
* rcu_access_pointer() - fetch RCU pointer with no dereferencing
* @p: The pointer to read
*
* 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. Although rcu_access_pointer() may also be used in cases where
* update-side locks prevent the value of the pointer from changing, you
* should instead use rcu_dereference_protected() for this use case.
*
* It is also permissible to use rcu_access_pointer() when read-side
* access to the pointer was removed at least one grace period ago, as
* is the case in the context of the RCU callback that is freeing up
* the data, or after a synchronize_rcu() returns. This can be useful
* when tearing down multi-linked structures after a grace period
* has elapsed.
*/
#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
/**
* 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.
* An implicit check for being in an RCU read-side critical section
* (rcu_read_lock()) is included.
*
* For example:
*
* bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
*
* could be used to indicate to lockdep that foo->bar may only be dereferenced
* if either 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, lockdep_is_held(&foo->lock) ||
* atomic_read(&foo->usage) == 0);
*
* Inserts memory barriers on architectures that require them
* (currently only the Alpha), prevents the compiler from refetching
* (and from merging fetches), and, more importantly, documents exactly
* which pointers are protected by RCU and checks that the pointer is
* annotated as __rcu.
*/
#define rcu_dereference_check(p, c) \
__rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
/**
* rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
* @p: The pointer to read, prior to dereferencing
* @c: The conditions under which the dereference will take place
*
* This is the RCU-bh counterpart to rcu_dereference_check().
*/
#define rcu_dereference_bh_check(p, c) \
__rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
/**
* rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
* @p: The pointer to read, prior to dereferencing
* @c: The conditions under which the dereference will take place
*
* This is the RCU-sched counterpart to rcu_dereference_check().
*/
#define rcu_dereference_sched_check(p, c) \
__rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
__rcu)
#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
/**
* rcu_access_index() - fetch RCU index with no dereferencing
* @p: The index to read
*
* Return the value of the specified RCU-protected index, but omit the
* smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
* when the value of this index is accessed, but the index is not
* dereferenced, for example, when testing an RCU-protected index against
* -1. Although rcu_access_index() may also be used in cases where
* update-side locks prevent the value of the index from changing, you
* should instead use rcu_dereference_index_protected() for this use case.
*/
#define rcu_access_index(p) __rcu_access_index((p), __rcu)
/**
* rcu_dereference_index_check() - rcu_dereference for indices with debug checking
* @p: The pointer to read, prior to dereferencing
* @c: The conditions under which the dereference will take place
*
* Similar to rcu_dereference_check(), but omits the sparse checking.
* This allows rcu_dereference_index_check() to be used on integers,
* which can then be used as array indices. Attempting to use
* rcu_dereference_check() on an integer will give compiler warnings
* because the sparse address-space mechanism relies on dereferencing
* the RCU-protected pointer. Dereferencing integers is not something
* that even gcc will put up with.
*
* Note that this function does not implicitly check for RCU read-side
* critical sections. If this function gains lots of uses, it might
* make sense to provide versions for each flavor of RCU, but it does
* not make sense as of early 2010.
*/
#define rcu_dereference_index_check(p, c) \
__rcu_dereference_index_check((p), (c))
/**
* rcu_dereference_protected() - fetch RCU pointer when updates prevented
* @p: The pointer to read, prior to dereferencing
* @c: The conditions under which the dereference will take place
*
* 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.
*
* This function is only for update-side use. Using this function
* when protected only by rcu_read_lock() will result in infrequent
* but very ugly failures.
*/
#define rcu_dereference_protected(p, c) \
__rcu_dereference_protected((p), (c), __rcu)
/**
* rcu_dereference() - fetch RCU-protected pointer for dereferencing
* @p: The pointer to read, prior to dereferencing
*
* This is a simple wrapper around rcu_dereference_check().
*/
#define rcu_dereference(p) rcu_dereference_check(p, 0)
/**
* rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
* @p: The pointer to read, prior to dereferencing
*
* Makes rcu_dereference_check() do the dirty work.
*/
#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
/**
* rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
* @p: The pointer to read, prior to dereferencing
*
* Makes rcu_dereference_check() do the dirty work.
*/
#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
/**
* rcu_read_lock() - mark the beginning of an RCU read-side critical section
*
* When synchronize_rcu() is invoked on one CPU while other CPUs
* are within RCU read-side critical sections, then the
* synchronize_rcu() is guaranteed to block until after all the other
* CPUs exit their critical sections. Similarly, if call_rcu() is invoked
* on one CPU while other CPUs are within RCU read-side critical
* sections, invocation of the corresponding RCU callback is deferred
* until after the all the other CPUs exit their critical sections.
*
* Note, however, that RCU callbacks are permitted to run concurrently
* with new RCU read-side critical sections. One way that this can happen
* is via the following sequence of events: (1) CPU 0 enters an RCU
* read-side critical section, (2) CPU 1 invokes call_rcu() to register
* an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
* (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
* callback is invoked. This is legal, because the RCU read-side critical
* section that was running concurrently with the call_rcu() (and which
* therefore might be referencing something that the corresponding RCU
* callback would free up) has completed before the corresponding
* RCU callback is invoked.
*
* RCU read-side critical sections may be nested. Any deferred actions
* will be deferred until the outermost RCU read-side critical section
* completes.
*
* You can avoid reading and understanding the next paragraph by
* following this rule: don't put anything in an rcu_read_lock() RCU
* read-side critical section that would block in a !PREEMPT kernel.
* But if you want the full story, read on!
*
* In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it
* is illegal to block while in an RCU read-side critical section. In
* preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU)
* in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may
* be preempted, but explicit blocking is illegal. Finally, in preemptible
* RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds,
* RCU read-side critical sections may be preempted and they may also
* block, but only when acquiring spinlocks that are subject to priority
* inheritance.
*/
static inline void rcu_read_lock(void)
{
__rcu_read_lock();
__acquire(RCU);
rcu_lock_acquire(&rcu_lock_map);
rcu_lockdep_assert(!rcu_is_cpu_idle(),
"rcu_read_lock() used illegally while idle");
}
/*
* So where is rcu_write_lock()? It does not exist, as there is no
* way for writers to lock out RCU readers. This is a feature, not
* a bug -- this property is what provides RCU's performance benefits.
* Of course, writers must coordinate with each other. The normal
* spinlock primitives work well for this, but any other technique may be
* used as well. RCU does not care how the writers keep out of each
* others' way, as long as they do so.
*/
/**
* rcu_read_unlock() - marks the end of an RCU read-side critical section.
*
* See rcu_read_lock() for more information.
*/
static inline void rcu_read_unlock(void)
{
rcu_lockdep_assert(!rcu_is_cpu_idle(),
"rcu_read_unlock() used illegally while idle");
rcu_lock_release(&rcu_lock_map);
__release(RCU);
__rcu_read_unlock();
}
/**
* rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
*
* This is equivalent of rcu_read_lock(), but to be used when updates
* are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
* both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
* softirq handler to be a quiescent state, a process in RCU read-side
* critical section must be protected by disabling softirqs. Read-side
* critical sections in interrupt context can use just rcu_read_lock(),
* though this should at least be commented to avoid confusing people
* reading the code.
*
* Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
* must occur in the same context, for example, it is illegal to invoke
* rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
* was invoked from some other task.
*/
static inline void rcu_read_lock_bh(void)
{
local_bh_disable();
__acquire(RCU_BH);
rcu_lock_acquire(&rcu_bh_lock_map);
rcu_lockdep_assert(!rcu_is_cpu_idle(),
"rcu_read_lock_bh() used illegally while idle");
}
/*
* rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
*
* See rcu_read_lock_bh() for more information.
*/
static inline void rcu_read_unlock_bh(void)
{
rcu_lockdep_assert(!rcu_is_cpu_idle(),
"rcu_read_unlock_bh() used illegally while idle");
rcu_lock_release(&rcu_bh_lock_map);
__release(RCU_BH);
local_bh_enable();
}
/**
* rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
*
* This is equivalent of rcu_read_lock(), but to be used when updates
* are being done using call_rcu_sched() or synchronize_rcu_sched().
* Read-side critical sections can also be introduced by anything that
* disables preemption, including local_irq_disable() and friends.
*
* Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
* must occur in the same context, for example, it is illegal to invoke
* rcu_read_unlock_sched() from process context if the matching
* rcu_read_lock_sched() was invoked from an NMI handler.
*/
static inline void rcu_read_lock_sched(void)
{
preempt_disable();
__acquire(RCU_SCHED);
rcu_lock_acquire(&rcu_sched_lock_map);
rcu_lockdep_assert(!rcu_is_cpu_idle(),
"rcu_read_lock_sched() used illegally while idle");
}
/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
static inline notrace void rcu_read_lock_sched_notrace(void)
{
preempt_disable_notrace();
__acquire(RCU_SCHED);
}
/*
* rcu_read_unlock_sched - marks the end of a RCU-classic critical section
*
* See rcu_read_lock_sched for more information.
*/
static inline void rcu_read_unlock_sched(void)
{
rcu_lockdep_assert(!rcu_is_cpu_idle(),
"rcu_read_unlock_sched() used illegally while idle");
rcu_lock_release(&rcu_sched_lock_map);
__release(RCU_SCHED);
preempt_enable();
}
/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
static inline notrace void rcu_read_unlock_sched_notrace(void)
{
__release(RCU_SCHED);
preempt_enable_notrace();
}
/**
* rcu_assign_pointer() - assign to RCU-protected pointer
* @p: pointer to assign to
* @v: value to assign (publish)
*
* Assigns the specified value to the specified RCU-protected
* pointer, ensuring that any concurrent RCU readers will see
* any prior initialization. Returns the value assigned.
*
* Inserts memory barriers on architectures that require them
* (which is most of them), and also prevents the compiler from
* reordering the code that initializes the structure after the pointer
* assignment. More importantly, this call documents which pointers
* will be dereferenced by RCU read-side code.
*
* In some special cases, you may use RCU_INIT_POINTER() instead
* of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
* to the fact that it does not constrain either the CPU or the compiler.
* That said, using RCU_INIT_POINTER() when you should have used
* rcu_assign_pointer() is a very bad thing that results in
* impossible-to-diagnose memory corruption. So please be careful.
* See the RCU_INIT_POINTER() comment header for details.
*/
#define rcu_assign_pointer(p, v) \
__rcu_assign_pointer((p), (v), __rcu)
/**
* RCU_INIT_POINTER() - initialize an RCU protected pointer
*
* Initialize an RCU-protected pointer in special cases where readers
* do not need ordering constraints on the CPU or the compiler. These
* special cases are:
*
* 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
* 2. The caller has taken whatever steps are required to prevent
* RCU readers from concurrently accessing this pointer -or-
* 3. The referenced data structure has already been exposed to
* readers either at compile time or via rcu_assign_pointer() -and-
* a. You have not made -any- reader-visible changes to
* this structure since then -or-
* b. It is OK for readers accessing this structure from its
* new location to see the old state of the structure. (For
* example, the changes were to statistical counters or to
* other state where exact synchronization is not required.)
*
* Failure to follow these rules governing use of RCU_INIT_POINTER() will
* result in impossible-to-diagnose memory corruption. As in the structures
* will look OK in crash dumps, but any concurrent RCU readers might
* see pre-initialized values of the referenced data structure. So
* please be very careful how you use RCU_INIT_POINTER()!!!
*
* If you are creating an RCU-protected linked structure that is accessed
* by a single external-to-structure RCU-protected pointer, then you may
* use RCU_INIT_POINTER() to initialize the internal RCU-protected
* pointers, but you must use rcu_assign_pointer() to initialize the
* external-to-structure pointer -after- you have completely initialized
* the reader-accessible portions of the linked structure.
*/
#define RCU_INIT_POINTER(p, v) \
p = (typeof(*v) __force __rcu *)(v)
static __always_inline bool __is_kfree_rcu_offset(unsigned long offset)
{
return offset < 4096;
}
static __always_inline
void __kfree_rcu(struct rcu_head *head, unsigned long offset)
{
typedef void (*rcu_callback)(struct rcu_head *);
BUILD_BUG_ON(!__builtin_constant_p(offset));
/* See the kfree_rcu() header comment. */
BUILD_BUG_ON(!__is_kfree_rcu_offset(offset));
kfree_call_rcu(head, (rcu_callback)offset);
}
/**
* kfree_rcu() - kfree an object after a grace period.
* @ptr: pointer to kfree
* @rcu_head: the name of the struct rcu_head within the type of @ptr.
*
* Many rcu callbacks functions just call kfree() on the base structure.
* These functions are trivial, but their size adds up, and furthermore
* when they are used in a kernel module, that module must invoke the
* high-latency rcu_barrier() function at module-unload time.
*
* The kfree_rcu() function handles this issue. Rather than encoding a
* function address in the embedded rcu_head structure, kfree_rcu() instead
* encodes the offset of the rcu_head structure within the base structure.
* Because the functions are not allowed in the low-order 4096 bytes of
* kernel virtual memory, offsets up to 4095 bytes can be accommodated.
* If the offset is larger than 4095 bytes, a compile-time error will
* be generated in __kfree_rcu(). If this error is triggered, you can
* either fall back to use of call_rcu() or rearrange the structure to
* position the rcu_head structure into the first 4096 bytes.
*
* Note that the allowable offset might decrease in the future, for example,
* to allow something like kmem_cache_free_rcu().
*/
#define kfree_rcu(ptr, rcu_head) \
__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
#endif /* __LINUX_RCUPDATE_H */
