mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-26 19:00:25 +00:00
![Neeraj Upadhyay](/assets/img/avatar_default.png)
The rcu_head_after_call_rcu() function reads the rhp->func pointer twice, which can result in a false-positive WARN_ON_ONCE() if the callback were passed to call_rcu() between the two reads. Although racing rcu_head_after_call_rcu() with call_rcu() is to be a dubious use case (the return value is not reliable in that case), intermittent and irreproducible warnings are also quite dubious. This commit therefore uses a single READ_ONCE() to pick up the value of rhp->func once, then tests that value twice, thus guaranteeing consistent processing within rcu_head_after_call_rcu()(). Neverthless, racing rcu_head_after_call_rcu() with call_rcu() is still a dubious use case. Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> [ paulmck: Add blank line after declaration per checkpatch.pl. ] Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
889 lines
32 KiB
C
889 lines
32 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
|
|
/*
|
|
* Read-Copy Update mechanism for mutual exclusion
|
|
*
|
|
* Copyright IBM Corporation, 2001
|
|
*
|
|
* Author: Dipankar Sarma <dipankar@in.ibm.com>
|
|
*
|
|
* Based on the original work by Paul McKenney <paulmck@vnet.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/compiler.h>
|
|
#include <linux/atomic.h>
|
|
#include <linux/irqflags.h>
|
|
#include <linux/preempt.h>
|
|
#include <linux/bottom_half.h>
|
|
#include <linux/lockdep.h>
|
|
#include <asm/processor.h>
|
|
#include <linux/cpumask.h>
|
|
|
|
#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
|
|
#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
|
|
#define ulong2long(a) (*(long *)(&(a)))
|
|
|
|
/* Exported common interfaces */
|
|
void call_rcu(struct rcu_head *head, rcu_callback_t func);
|
|
void rcu_barrier_tasks(void);
|
|
void synchronize_rcu(void);
|
|
|
|
#ifdef CONFIG_PREEMPT_RCU
|
|
|
|
void __rcu_read_lock(void);
|
|
void __rcu_read_unlock(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)
|
|
{
|
|
if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
|
|
preempt_disable();
|
|
}
|
|
|
|
static inline void __rcu_read_unlock(void)
|
|
{
|
|
if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
|
|
preempt_enable();
|
|
}
|
|
|
|
static inline int rcu_preempt_depth(void)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
|
|
|
|
/* Internal to kernel */
|
|
void rcu_init(void);
|
|
extern int rcu_scheduler_active __read_mostly;
|
|
void rcu_sched_clock_irq(int user);
|
|
void rcu_report_dead(unsigned int cpu);
|
|
void rcutree_migrate_callbacks(int cpu);
|
|
|
|
#ifdef CONFIG_RCU_STALL_COMMON
|
|
void rcu_sysrq_start(void);
|
|
void rcu_sysrq_end(void);
|
|
#else /* #ifdef CONFIG_RCU_STALL_COMMON */
|
|
static inline void rcu_sysrq_start(void) { }
|
|
static inline void rcu_sysrq_end(void) { }
|
|
#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
|
|
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
void rcu_user_enter(void);
|
|
void rcu_user_exit(void);
|
|
#else
|
|
static inline void rcu_user_enter(void) { }
|
|
static inline void rcu_user_exit(void) { }
|
|
#endif /* CONFIG_NO_HZ_FULL */
|
|
|
|
#ifdef CONFIG_RCU_NOCB_CPU
|
|
void rcu_init_nohz(void);
|
|
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
|
|
static inline void rcu_init_nohz(void) { }
|
|
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
|
|
|
|
/**
|
|
* RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
|
|
* @a: Code that RCU needs to pay attention to.
|
|
*
|
|
* RCU read-side critical sections are forbidden in the inner idle loop,
|
|
* that is, between the rcu_idle_enter() and the rcu_idle_exit() -- RCU
|
|
* will happily ignore any such read-side critical sections. However,
|
|
* things like powertop need tracepoints in the inner idle loop.
|
|
*
|
|
* This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
|
|
* will tell RCU that it needs to pay attention, invoke its argument
|
|
* (in this example, calling the do_something_with_RCU() function),
|
|
* and then tell RCU to go back to ignoring this CPU. It is permissible
|
|
* to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is
|
|
* on the order of a million or so, even on 32-bit systems). It is
|
|
* not legal to block within RCU_NONIDLE(), nor is it permissible to
|
|
* transfer control either into or out of RCU_NONIDLE()'s statement.
|
|
*/
|
|
#define RCU_NONIDLE(a) \
|
|
do { \
|
|
rcu_irq_enter_irqson(); \
|
|
do { a; } while (0); \
|
|
rcu_irq_exit_irqson(); \
|
|
} while (0)
|
|
|
|
/*
|
|
* Note a quasi-voluntary context switch for RCU-tasks's benefit.
|
|
* This is a macro rather than an inline function to avoid #include hell.
|
|
*/
|
|
#ifdef CONFIG_TASKS_RCU
|
|
#define rcu_tasks_qs(t) \
|
|
do { \
|
|
if (READ_ONCE((t)->rcu_tasks_holdout)) \
|
|
WRITE_ONCE((t)->rcu_tasks_holdout, false); \
|
|
} while (0)
|
|
#define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t)
|
|
void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
|
|
void synchronize_rcu_tasks(void);
|
|
void exit_tasks_rcu_start(void);
|
|
void exit_tasks_rcu_finish(void);
|
|
#else /* #ifdef CONFIG_TASKS_RCU */
|
|
#define rcu_tasks_qs(t) do { } while (0)
|
|
#define rcu_note_voluntary_context_switch(t) do { } while (0)
|
|
#define call_rcu_tasks call_rcu
|
|
#define synchronize_rcu_tasks synchronize_rcu
|
|
static inline void exit_tasks_rcu_start(void) { }
|
|
static inline void exit_tasks_rcu_finish(void) { }
|
|
#endif /* #else #ifdef CONFIG_TASKS_RCU */
|
|
|
|
/**
|
|
* cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
|
|
*
|
|
* This macro resembles cond_resched(), except that it is defined to
|
|
* report potential quiescent states to RCU-tasks even if the cond_resched()
|
|
* machinery were to be shut off, as some advocate for PREEMPT kernels.
|
|
*/
|
|
#define cond_resched_tasks_rcu_qs() \
|
|
do { \
|
|
rcu_tasks_qs(current); \
|
|
cond_resched(); \
|
|
} while (0)
|
|
|
|
/*
|
|
* Infrastructure to implement the synchronize_() primitives in
|
|
* TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
|
|
*/
|
|
|
|
#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
|
|
#include <linux/rcutree.h>
|
|
#elif defined(CONFIG_TINY_RCU)
|
|
#include <linux/rcutiny.h>
|
|
#else
|
|
#error "Unknown RCU implementation specified to kernel configuration"
|
|
#endif
|
|
|
|
/*
|
|
* The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
|
|
* are needed for dynamic initialization and destruction of rcu_head
|
|
* on the stack, and init_rcu_head()/destroy_rcu_head() are needed for
|
|
* dynamic initialization and destruction of statically allocated rcu_head
|
|
* structures. However, rcu_head structures allocated dynamically in the
|
|
* heap don't need any initialization.
|
|
*/
|
|
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
|
|
void init_rcu_head(struct rcu_head *head);
|
|
void destroy_rcu_head(struct rcu_head *head);
|
|
void init_rcu_head_on_stack(struct rcu_head *head);
|
|
void destroy_rcu_head_on_stack(struct rcu_head *head);
|
|
#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
|
|
static inline void init_rcu_head(struct rcu_head *head) { }
|
|
static inline void destroy_rcu_head(struct rcu_head *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 true; }
|
|
#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
|
|
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
|
|
|
static inline void rcu_lock_acquire(struct lockdep_map *map)
|
|
{
|
|
lock_acquire(map, 0, 0, 2, 0, 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 struct lockdep_map rcu_callback_map;
|
|
int debug_lockdep_rcu_enabled(void);
|
|
int rcu_read_lock_held(void);
|
|
int rcu_read_lock_bh_held(void);
|
|
int rcu_read_lock_sched_held(void);
|
|
|
|
#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;
|
|
}
|
|
|
|
static inline int rcu_read_lock_sched_held(void)
|
|
{
|
|
return !preemptible();
|
|
}
|
|
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
|
|
|
|
#ifdef CONFIG_PROVE_RCU
|
|
|
|
/**
|
|
* RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
|
|
* @c: condition to check
|
|
* @s: informative message
|
|
*/
|
|
#define RCU_LOCKDEP_WARN(c, s) \
|
|
do { \
|
|
static bool __section(.data.unlikely) __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_WARN(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_WARN(lock_is_held(&rcu_bh_lock_map), \
|
|
"Illegal context switch in RCU-bh read-side critical section"); \
|
|
RCU_LOCKDEP_WARN(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_WARN(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 pointers markings to match different RCU implementations
|
|
* (e.g., __srcu), should this make sense in the future.
|
|
*/
|
|
|
|
#ifdef __CHECKER__
|
|
#define rcu_check_sparse(p, space) \
|
|
((void)(((typeof(*p) space *)p) == p))
|
|
#else /* #ifdef __CHECKER__ */
|
|
#define rcu_check_sparse(p, space)
|
|
#endif /* #else #ifdef __CHECKER__ */
|
|
|
|
#define __rcu_access_pointer(p, space) \
|
|
({ \
|
|
typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
|
|
rcu_check_sparse(p, space); \
|
|
((typeof(*p) __force __kernel *)(_________p1)); \
|
|
})
|
|
#define __rcu_dereference_check(p, c, space) \
|
|
({ \
|
|
/* Dependency order vs. p above. */ \
|
|
typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
|
|
RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
|
|
rcu_check_sparse(p, space); \
|
|
((typeof(*p) __force __kernel *)(________p1)); \
|
|
})
|
|
#define __rcu_dereference_protected(p, c, space) \
|
|
({ \
|
|
RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
|
|
rcu_check_sparse(p, space); \
|
|
((typeof(*p) __force __kernel *)(p)); \
|
|
})
|
|
#define rcu_dereference_raw(p) \
|
|
({ \
|
|
/* Dependency order vs. p above. */ \
|
|
typeof(p) ________p1 = READ_ONCE(p); \
|
|
((typeof(*p) __force __kernel *)(________p1)); \
|
|
})
|
|
|
|
/**
|
|
* RCU_INITIALIZER() - statically initialize an RCU-protected global variable
|
|
* @v: The value to statically initialize with.
|
|
*/
|
|
#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
|
|
|
|
/**
|
|
* 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.
|
|
*
|
|
* 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.
|
|
*
|
|
* Note that rcu_assign_pointer() evaluates each of its arguments only
|
|
* once, appearances notwithstanding. One of the "extra" evaluations
|
|
* is in typeof() and the other visible only to sparse (__CHECKER__),
|
|
* neither of which actually execute the argument. As with most cpp
|
|
* macros, this execute-arguments-only-once property is important, so
|
|
* please be careful when making changes to rcu_assign_pointer() and the
|
|
* other macros that it invokes.
|
|
*/
|
|
#define rcu_assign_pointer(p, v) \
|
|
({ \
|
|
uintptr_t _r_a_p__v = (uintptr_t)(v); \
|
|
rcu_check_sparse(p, __rcu); \
|
|
\
|
|
if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
|
|
WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
|
|
else \
|
|
smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
|
|
_r_a_p__v; \
|
|
})
|
|
|
|
/**
|
|
* rcu_swap_protected() - swap an RCU and a regular pointer
|
|
* @rcu_ptr: RCU pointer
|
|
* @ptr: regular pointer
|
|
* @c: the conditions under which the dereference will take place
|
|
*
|
|
* Perform swap(@rcu_ptr, @ptr) where @rcu_ptr is an RCU-annotated pointer and
|
|
* @c is the argument that is passed to the rcu_dereference_protected() call
|
|
* used to read that pointer.
|
|
*/
|
|
#define rcu_swap_protected(rcu_ptr, ptr, c) do { \
|
|
typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \
|
|
rcu_assign_pointer((rcu_ptr), (ptr)); \
|
|
(ptr) = __tmp; \
|
|
} while (0)
|
|
|
|
/**
|
|
* 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
|
|
* lockdep checks for being in an RCU read-side critical section. 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), (c) || rcu_read_lock_held(), __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), (c) || rcu_read_lock_bh_held(), __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), (c) || rcu_read_lock_sched_held(), \
|
|
__rcu)
|
|
|
|
/*
|
|
* The tracing infrastructure traces RCU (we want that), but unfortunately
|
|
* some of the RCU checks causes tracing to lock up the system.
|
|
*
|
|
* The no-tracing version of rcu_dereference_raw() must not call
|
|
* rcu_read_lock_held().
|
|
*/
|
|
#define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
|
|
|
|
/**
|
|
* 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
|
|
* the READ_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_pointer_handoff() - Hand off a pointer from RCU to other mechanism
|
|
* @p: The pointer to hand off
|
|
*
|
|
* This is simply an identity function, but it documents where a pointer
|
|
* is handed off from RCU to some other synchronization mechanism, for
|
|
* example, reference counting or locking. In C11, it would map to
|
|
* kill_dependency(). It could be used as follows::
|
|
*
|
|
* rcu_read_lock();
|
|
* p = rcu_dereference(gp);
|
|
* long_lived = is_long_lived(p);
|
|
* if (long_lived) {
|
|
* if (!atomic_inc_not_zero(p->refcnt))
|
|
* long_lived = false;
|
|
* else
|
|
* p = rcu_pointer_handoff(p);
|
|
* }
|
|
* rcu_read_unlock();
|
|
*/
|
|
#define rcu_pointer_handoff(p) (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
|
|
* 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 (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 (with -rt patchset) 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_WARN(!rcu_is_watching(),
|
|
"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.
|
|
*
|
|
* In most situations, rcu_read_unlock() is immune from deadlock.
|
|
* However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
|
|
* is responsible for deboosting, which it does via rt_mutex_unlock().
|
|
* Unfortunately, this function acquires the scheduler's runqueue and
|
|
* priority-inheritance spinlocks. This means that deadlock could result
|
|
* if the caller of rcu_read_unlock() already holds one of these locks or
|
|
* any lock that is ever acquired while holding them.
|
|
*
|
|
* That said, RCU readers are never priority boosted unless they were
|
|
* preempted. Therefore, one way to avoid deadlock is to make sure
|
|
* that preemption never happens within any RCU read-side critical
|
|
* section whose outermost rcu_read_unlock() is called with one of
|
|
* rt_mutex_unlock()'s locks held. Such preemption can be avoided in
|
|
* a number of ways, for example, by invoking preempt_disable() before
|
|
* critical section's outermost rcu_read_lock().
|
|
*
|
|
* Given that the set of locks acquired by rt_mutex_unlock() might change
|
|
* at any time, a somewhat more future-proofed approach is to make sure
|
|
* that that preemption never happens within any RCU read-side critical
|
|
* section whose outermost rcu_read_unlock() is called with irqs disabled.
|
|
* This approach relies on the fact that rt_mutex_unlock() currently only
|
|
* acquires irq-disabled locks.
|
|
*
|
|
* The second of these two approaches is best in most situations,
|
|
* however, the first approach can also be useful, at least to those
|
|
* developers willing to keep abreast of the set of locks acquired by
|
|
* rt_mutex_unlock().
|
|
*
|
|
* See rcu_read_lock() for more information.
|
|
*/
|
|
static inline void rcu_read_unlock(void)
|
|
{
|
|
RCU_LOCKDEP_WARN(!rcu_is_watching(),
|
|
"rcu_read_unlock() used illegally while idle");
|
|
__release(RCU);
|
|
__rcu_read_unlock();
|
|
rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
|
|
}
|
|
|
|
/**
|
|
* rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
|
|
*
|
|
* This is equivalent of rcu_read_lock(), but also disables softirqs.
|
|
* Note that anything else that disables softirqs can also serve as
|
|
* an RCU read-side critical section.
|
|
*
|
|
* 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_WARN(!rcu_is_watching(),
|
|
"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_WARN(!rcu_is_watching(),
|
|
"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 disables preemption.
|
|
* Read-side critical sections can also be introduced by anything else
|
|
* 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_WARN(!rcu_is_watching(),
|
|
"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_WARN(!rcu_is_watching(),
|
|
"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_INIT_POINTER() - initialize an RCU protected pointer
|
|
* @p: The pointer to be initialized.
|
|
* @v: The value to initialized the pointer to.
|
|
*
|
|
* 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.
|
|
*
|
|
* Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
|
|
* ordering guarantees for either the CPU or the compiler.
|
|
*/
|
|
#define RCU_INIT_POINTER(p, v) \
|
|
do { \
|
|
rcu_check_sparse(p, __rcu); \
|
|
WRITE_ONCE(p, RCU_INITIALIZER(v)); \
|
|
} while (0)
|
|
|
|
/**
|
|
* RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
|
|
* @p: The pointer to be initialized.
|
|
* @v: The value to initialized the pointer to.
|
|
*
|
|
* GCC-style initialization for an RCU-protected pointer in a structure field.
|
|
*/
|
|
#define RCU_POINTER_INITIALIZER(p, v) \
|
|
.p = RCU_INITIALIZER(v)
|
|
|
|
/*
|
|
* Does the specified offset indicate that the corresponding rcu_head
|
|
* structure can be handled by kfree_rcu()?
|
|
*/
|
|
#define __is_kfree_rcu_offset(offset) ((offset) < 4096)
|
|
|
|
/*
|
|
* Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
|
|
*/
|
|
#define __kfree_rcu(head, offset) \
|
|
do { \
|
|
BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
|
|
kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
|
|
} while (0)
|
|
|
|
/**
|
|
* 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().
|
|
*
|
|
* The BUILD_BUG_ON check must not involve any function calls, hence the
|
|
* checks are done in macros here.
|
|
*/
|
|
#define kfree_rcu(ptr, rcu_head) \
|
|
__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
|
|
|
|
|
|
/*
|
|
* Place this after a lock-acquisition primitive to guarantee that
|
|
* an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies
|
|
* if the UNLOCK and LOCK are executed by the same CPU or if the
|
|
* UNLOCK and LOCK operate on the same lock variable.
|
|
*/
|
|
#ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
|
|
#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
|
|
#else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
|
|
#define smp_mb__after_unlock_lock() do { } while (0)
|
|
#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
|
|
|
|
|
|
/* Has the specified rcu_head structure been handed to call_rcu()? */
|
|
|
|
/**
|
|
* rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
|
|
* @rhp: The rcu_head structure to initialize.
|
|
*
|
|
* If you intend to invoke rcu_head_after_call_rcu() to test whether a
|
|
* given rcu_head structure has already been passed to call_rcu(), then
|
|
* you must also invoke this rcu_head_init() function on it just after
|
|
* allocating that structure. Calls to this function must not race with
|
|
* calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
|
|
*/
|
|
static inline void rcu_head_init(struct rcu_head *rhp)
|
|
{
|
|
rhp->func = (rcu_callback_t)~0L;
|
|
}
|
|
|
|
/**
|
|
* rcu_head_after_call_rcu - Has this rcu_head been passed to call_rcu()?
|
|
* @rhp: The rcu_head structure to test.
|
|
* @f: The function passed to call_rcu() along with @rhp.
|
|
*
|
|
* Returns @true if the @rhp has been passed to call_rcu() with @func,
|
|
* and @false otherwise. Emits a warning in any other case, including
|
|
* the case where @rhp has already been invoked after a grace period.
|
|
* Calls to this function must not race with callback invocation. One way
|
|
* to avoid such races is to enclose the call to rcu_head_after_call_rcu()
|
|
* in an RCU read-side critical section that includes a read-side fetch
|
|
* of the pointer to the structure containing @rhp.
|
|
*/
|
|
static inline bool
|
|
rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
|
|
{
|
|
rcu_callback_t func = READ_ONCE(rhp->func);
|
|
|
|
if (func == f)
|
|
return true;
|
|
WARN_ON_ONCE(func != (rcu_callback_t)~0L);
|
|
return false;
|
|
}
|
|
|
|
#endif /* __LINUX_RCUPDATE_H */
|