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rcu: define __rcu address space modifier for sparse

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This commit provides definitions for the __rcu annotation defined earlier.
This annotation permits sparse to check for correct use of RCU-protected
pointers.  If a pointer that is annotated with __rcu is accessed
directly (as opposed to via rcu_dereference(), rcu_assign_pointer(),
or one of their variants), sparse can be made to complain.  To enable
such complaints, use the new default-disabled CONFIG_SPARSE_RCU_POINTER
kernel configuration option.  Please note that these sparse complaints are
intended to be a debugging aid, -not- a code-style-enforcement mechanism.

There are special rcu_dereference_protected() and rcu_access_pointer()
accessors for use when RCU read-side protection is not required, for
example, when no other CPU has access to the data structure in question
or while the current CPU hold the update-side lock.

This patch also updates a number of docbook comments that were showing
their age.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Christopher Li <sparse@chrisli.org>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Paul E. McKenney 2010-04-28 14:39:09 -07:00
parent d34a16661e
commit ca5ecddfa8
5 changed files with 260 additions and 148 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/linux/compiler.h
View File

@ -16,7 +16,11 @@
# define __release(x) __context__(x,-1)
# define __cond_lock(x,c) ((c) ? ({ __acquire(x); 1; }) : 0)
# define __percpu __attribute__((noderef, address_space(3)))
#ifdef CONFIG_SPARSE_RCU_POINTER
# define __rcu __attribute__((noderef, address_space(4)))
#else
# define __rcu
#endif
extern void __chk_user_ptr(const volatile void __user *);
extern void __chk_io_ptr(const volatile void __iomem *);
#else

358
include/linux/rcupdate.h
View File

@ -41,6 +41,7 @@
#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 */
@ -120,14 +121,15 @@ 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?
* 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.
* prove otherwise. This is useful for debug checks in functions that
* require that they be called within an RCU read-side critical section.
*
* Check debug_lockdep_rcu_enabled() to prevent false positives during boot
* Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
* and while lockdep is disabled.
*/
static inline int rcu_read_lock_held(void)
@ -144,14 +146,16 @@ static inline int rcu_read_lock_held(void)
extern int rcu_read_lock_bh_held(void);
/**
* rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section?
* 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.
* 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.
@ -220,41 +224,155 @@ extern int rcu_my_thread_group_empty(void);
} \
} while (0)
#else /* #ifdef CONFIG_PROVE_RCU */
#define __do_rcu_dereference_check(c) 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.
*/
#define __rcu_access_pointer(p, space) \
({ \
typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
(void) (((typeof (*p) space *)p) == p); \
((typeof(*p) __force __kernel *)(_________p1)); \
})
#define __rcu_dereference_check(p, c, space) \
({ \
typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
__do_rcu_dereference_check(c); \
(void) (((typeof (*p) space *)p) == p); \
smp_read_barrier_depends(); \
((typeof(*p) __force __kernel *)(_________p1)); \
})
#define __rcu_dereference_protected(p, c, space) \
({ \
__do_rcu_dereference_check(c); \
(void) (((typeof (*p) space *)p) == p); \
((typeof(*p) __force __kernel *)(p)); \
})
#define __rcu_dereference_index_check(p, c) \
({ \
typeof(p) _________p1 = ACCESS_ONCE(p); \
__do_rcu_dereference_check(c); \
smp_read_barrier_depends(); \
(_________p1); \
})
#define __rcu_assign_pointer(p, v, space) \
({ \
if (!__builtin_constant_p(v) || \
((v) != NULL)) \
smp_wmb(); \
(p) = (typeof(*v) __force space *)(v); \
})
/**
* rcu_dereference_check - rcu_dereference with debug checking
* 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.
*/
#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.
* 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, rcu_read_lock_held() ||
* lockdep_is_held(&foo->lock));
* 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 the RCU read lock is held, or that the lock required to replace
* 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, rcu_read_lock_held() ||
* lockdep_is_held(&foo->lock) ||
* 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) \
({ \
__do_rcu_dereference_check(c); \
rcu_dereference_raw(p); \
})
__rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
/**
* rcu_dereference_protected - fetch RCU pointer when updates prevented
* 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_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
@ -263,35 +381,61 @@ extern int rcu_my_thread_group_empty(void);
* 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) \
({ \
__do_rcu_dereference_check(c); \
(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_dereference_protected((p), (c), __rcu)
/**
* rcu_access_pointer - fetch RCU pointer with no dereferencing
* rcu_dereference_bh_protected() - fetch RCU-bh 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
* 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.
* This is the RCU-bh counterpart to rcu_dereference_protected().
*/
#define rcu_access_pointer(p) ACCESS_ONCE(p)
#define rcu_dereference_bh_protected(p, c) \
__rcu_dereference_protected((p), (c), __rcu)
/**
* rcu_read_lock - mark the beginning of an RCU read-side critical section.
* rcu_dereference_sched_protected() - fetch RCU-sched pointer when updates prevented
* @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_protected().
*/
#define rcu_dereference_sched_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
@ -337,7 +481,7 @@ static inline void rcu_read_lock(void)
*/
/**
* rcu_read_unlock - marks the end of an RCU read-side critical section.
* rcu_read_unlock() - marks the end of an RCU read-side critical section.
*
* See rcu_read_lock() for more information.
*/
@ -349,15 +493,16 @@ static inline void rcu_read_unlock(void)
}
/**
* rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
* 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(). Since call_rcu_bh() callbacks
* 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().
*
* 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.
*/
static inline void rcu_read_lock_bh(void)
{
@ -379,13 +524,12 @@ static inline void rcu_read_unlock_bh(void)
}
/**
* rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
* rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
*
* Should be used with either
* - synchronize_sched()
* or
* - call_rcu_sched() and rcu_barrier_sched()
* on the write-side to insure proper synchronization.
* 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.
*/
static inline void rcu_read_lock_sched(void)
{
@ -420,54 +564,14 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
preempt_enable_notrace();
}
/**
* rcu_dereference_raw - fetch an RCU-protected pointer
* rcu_assign_pointer() - assign to RCU-protected pointer
* @p: pointer to assign to
* @v: value to assign (publish)
*
* The caller must be within some flavor of RCU read-side critical
* section, or must be otherwise preventing the pointer from changing,
* for example, by holding an appropriate lock. This pointer may later
* be safely dereferenced. It is the caller's responsibility to have
* done the right thing, as this primitive does no checking of any kind.
*
* Inserts memory barriers on architectures that require them
* (currently only the Alpha), and, more importantly, documents
* exactly which pointers are protected by RCU.
*/
#define rcu_dereference_raw(p) ({ \
typeof(p) _________p1 = ACCESS_ONCE(p); \
smp_read_barrier_depends(); \
(_________p1); \
})
/**
* rcu_dereference - fetch an RCU-protected pointer, checking for RCU
*
* Makes rcu_dereference_check() do the dirty work.
*/
#define rcu_dereference(p) \
rcu_dereference_check(p, rcu_read_lock_held())
/**
* rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh
*
* Makes rcu_dereference_check() do the dirty work.
*/
#define rcu_dereference_bh(p) \
rcu_dereference_check(p, rcu_read_lock_bh_held())
/**
* rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
*
* Makes rcu_dereference_check() do the dirty work.
*/
#define rcu_dereference_sched(p) \
rcu_dereference_check(p, rcu_read_lock_sched_held())
/**
* rcu_assign_pointer - assign (publicize) a pointer to a newly
* initialized structure that will be dereferenced by RCU read-side
* critical sections. Returns the value assigned.
* 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
* (pretty much all of them other than x86), and also prevents
@ -476,14 +580,17 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
* call documents which pointers will be dereferenced by RCU read-side
* code.
*/
#define rcu_assign_pointer(p, v) \
({ \
if (!__builtin_constant_p(v) || \
((v) != NULL)) \
smp_wmb(); \
(p) = (v); \
})
__rcu_assign_pointer((p), (v), __rcu)
/**
* RCU_INIT_POINTER() - initialize an RCU protected pointer
*
* Initialize an RCU-protected pointer in such a way to avoid RCU-lockdep
* splats.
*/
#define RCU_INIT_POINTER(p, v) \
p = (typeof(*v) __force __rcu *)(v)
/* Infrastructure to implement the synchronize_() primitives. */
@ -495,7 +602,7 @@ struct rcu_synchronize {
extern void wakeme_after_rcu(struct rcu_head *head);
/**
* call_rcu - Queue an RCU callback for invocation after a grace period.
* call_rcu() - Queue an RCU callback for invocation after a grace period.
* @head: structure to be used for queueing the RCU updates.
* @func: actual update function to be invoked after the grace period
*
@ -509,7 +616,7 @@ extern void call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *head));
/**
* call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
* 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 update function to be invoked after the grace period
*
@ -566,37 +673,4 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head)
}
#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
#ifndef CONFIG_PROVE_RCU
#define __do_rcu_dereference_check(c) do { } while (0)
#endif /* #ifdef CONFIG_PROVE_RCU */
#define __rcu_dereference_index_check(p, c) \
({ \
typeof(p) _________p1 = ACCESS_ONCE(p); \
__do_rcu_dereference_check(c); \
smp_read_barrier_depends(); \
(_________p1); \
})
/**
* 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))
#endif /* __LINUX_RCUPDATE_H */

27
include/linux/srcu.h
View File

@ -108,12 +108,31 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp)
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
/**
* srcu_dereference - fetch SRCU-protected pointer with checking
* srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
* @p: the pointer to fetch and protect for later dereferencing
* @sp: pointer to the srcu_struct, which is used to check that we
* really are in an SRCU read-side critical section.
* @c: condition to check for update-side use
*
* Makes rcu_dereference_check() do the dirty work.
* If PROVE_RCU is enabled, invoking this outside of an RCU read-side
* critical section will result in an RCU-lockdep splat, unless @c evaluates
* to 1. The @c argument will normally be a logical expression containing
* lockdep_is_held() calls.
*/
#define srcu_dereference(p, sp) \
rcu_dereference_check(p, srcu_read_lock_held(sp))
#define srcu_dereference_check(p, sp, c) \
__rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
/**
* srcu_dereference - fetch SRCU-protected pointer for later dereferencing
* @p: the pointer to fetch and protect for later dereferencing
* @sp: pointer to the srcu_struct, which is used to check that we
* really are in an SRCU read-side critical section.
*
* Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
* is enabled, invoking this outside of an RCU read-side critical
* section will result in an RCU-lockdep splat.
*/
#define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
/**
* srcu_read_lock - register a new reader for an SRCU-protected structure.

6
kernel/rcupdate.c
View File

@ -73,12 +73,14 @@ int debug_lockdep_rcu_enabled(void)
EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
/**
* rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section?
* rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
*
* Check for bottom half being disabled, which covers both the
* CONFIG_PROVE_RCU and not cases. Note that if someone uses
* rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
* will show the situation.
* will show the situation. This is useful for debug checks in functions
* that require that they be called within an RCU read-side critical
* section.
*
* Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
*/

13
lib/Kconfig.debug
View File

@ -539,6 +539,19 @@ config PROVE_RCU_REPEATEDLY
disabling, allowing multiple RCU-lockdep warnings to be printed
on a single reboot.
config SPARSE_RCU_POINTER
bool "RCU debugging: sparse-based checks for pointer usage"
default n
help
This feature enables the __rcu sparse annotation for
RCU-protected pointers. This annotation will cause sparse
to flag any non-RCU used of annotated pointers. This can be
helpful when debugging RCU usage. Please note that this feature
is not intended to enforce code cleanliness; it is instead merely
a debugging aid.
Say Y to make sparse flag questionable use of RCU-protected pointers
Say N if you are unsure.
config LOCKDEP