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alistair23-linux/include/linux/spinlock.h
Heiko Carstens e81ce1f7ec [PATCH] timer/hrtimer: take per cpu locks in sane order 
Doing something like this on a two cpu system

  # echo 0 > /sys/devices/system/cpu/cpu0/online
  # echo 1 > /sys/devices/system/cpu/cpu0/online
  # echo 0 > /sys/devices/system/cpu/cpu1/online

will give me this:

  =======================================================
  [ INFO: possible circular locking dependency detected ]
  2.6.21-rc2-g562aa1d4-dirty #7
  -------------------------------------------------------
  bash/1282 is trying to acquire lock:
   (&cpu_base->lock_key){.+..}, at: [<000000000005f17e>] hrtimer_cpu_notify+0xc6/0x240

  but task is already holding lock:
   (&cpu_base->lock_key#2){.+..}, at: [<000000000005f174>] hrtimer_cpu_notify+0xbc/0x240

  which lock already depends on the new lock.

This happens because we have the following code in kernel/hrtimer.c:

  migrate_hrtimers(int cpu)
  [...]
  old_base = &per_cpu(hrtimer_bases, cpu);
  new_base = &get_cpu_var(hrtimer_bases);
  [...]
  spin_lock(&new_base->lock);
  spin_lock(&old_base->lock);

Which means the spinlocks are taken in an order which depends on which cpu
gets shut down from which other cpu. Therefore lockdep complains that there
might be an ABBA deadlock. Since migrate_hrtimers() gets only called on
cpu hotplug it's safe to assume that it isn't executed concurrently on a

The same problem exists in kernel/timer.c: migrate_timers().

As pointed out by Christian Borntraeger one possible solution to avoid
the locking order complaints would be to make sure that the locks are
always taken in the same order. E.g. by taking the lock of the cpu with
the lower number first.

To achieve this we introduce two new spinlock functions double_spin_lock
and double_spin_unlock which lock or unlock two locks in a given order.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Christian Borntraeger <cborntra@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-03-05 07:57:53 -08:00

343 lines
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#ifndef __LINUX_SPINLOCK_H
#define __LINUX_SPINLOCK_H
/*
* include/linux/spinlock.h - generic spinlock/rwlock declarations
*
* here's the role of the various spinlock/rwlock related include files:
*
* on SMP builds:
*
* asm/spinlock_types.h: contains the raw_spinlock_t/raw_rwlock_t and the
* initializers
*
* linux/spinlock_types.h:
* defines the generic type and initializers
*
* asm/spinlock.h: contains the __raw_spin_*()/etc. lowlevel
* implementations, mostly inline assembly code
*
* (also included on UP-debug builds:)
*
* linux/spinlock_api_smp.h:
* contains the prototypes for the _spin_*() APIs.
*
* linux/spinlock.h: builds the final spin_*() APIs.
*
* on UP builds:
*
* linux/spinlock_type_up.h:
* contains the generic, simplified UP spinlock type.
* (which is an empty structure on non-debug builds)
*
* linux/spinlock_types.h:
* defines the generic type and initializers
*
* linux/spinlock_up.h:
* contains the __raw_spin_*()/etc. version of UP
* builds. (which are NOPs on non-debug, non-preempt
* builds)
*
* (included on UP-non-debug builds:)
*
* linux/spinlock_api_up.h:
* builds the _spin_*() APIs.
*
* linux/spinlock.h: builds the final spin_*() APIs.
*/
#include <linux/preempt.h>
#include <linux/linkage.h>
#include <linux/compiler.h>
#include <linux/thread_info.h>
#include <linux/kernel.h>
#include <linux/stringify.h>
#include <linux/bottom_half.h>
#include <asm/system.h>
/*
* Must define these before including other files, inline functions need them
*/
#define LOCK_SECTION_NAME ".text.lock."KBUILD_BASENAME
#define LOCK_SECTION_START(extra) \
".subsection 1\n\t" \
extra \
".ifndef " LOCK_SECTION_NAME "\n\t" \
LOCK_SECTION_NAME ":\n\t" \
".endif\n"
#define LOCK_SECTION_END \
".previous\n\t"
#define __lockfunc fastcall __attribute__((section(".spinlock.text")))
/*
* Pull the raw_spinlock_t and raw_rwlock_t definitions:
*/
#include <linux/spinlock_types.h>
extern int __lockfunc generic__raw_read_trylock(raw_rwlock_t *lock);
/*
* Pull the __raw*() functions/declarations (UP-nondebug doesnt need them):
*/
#ifdef CONFIG_SMP
# include <asm/spinlock.h>
#else
# include <linux/spinlock_up.h>
#endif
#ifdef CONFIG_DEBUG_SPINLOCK
extern void __spin_lock_init(spinlock_t *lock, const char *name,
struct lock_class_key *key);
# define spin_lock_init(lock) \
do { \
static struct lock_class_key __key; \
\
__spin_lock_init((lock), #lock, &__key); \
} while (0)
#else
# define spin_lock_init(lock) \
do { *(lock) = SPIN_LOCK_UNLOCKED; } while (0)
#endif
#ifdef CONFIG_DEBUG_SPINLOCK
extern void __rwlock_init(rwlock_t *lock, const char *name,
struct lock_class_key *key);
# define rwlock_init(lock) \
do { \
static struct lock_class_key __key; \
\
__rwlock_init((lock), #lock, &__key); \
} while (0)
#else
# define rwlock_init(lock) \
do { *(lock) = RW_LOCK_UNLOCKED; } while (0)
#endif
#define spin_is_locked(lock) __raw_spin_is_locked(&(lock)->raw_lock)
/**
* spin_unlock_wait - wait until the spinlock gets unlocked
* @lock: the spinlock in question.
*/
#define spin_unlock_wait(lock) __raw_spin_unlock_wait(&(lock)->raw_lock)
/*
* Pull the _spin_*()/_read_*()/_write_*() functions/declarations:
*/
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
# include <linux/spinlock_api_smp.h>
#else
# include <linux/spinlock_api_up.h>
#endif
#ifdef CONFIG_DEBUG_SPINLOCK
extern void _raw_spin_lock(spinlock_t *lock);
#define _raw_spin_lock_flags(lock, flags) _raw_spin_lock(lock)
extern int _raw_spin_trylock(spinlock_t *lock);
extern void _raw_spin_unlock(spinlock_t *lock);
extern void _raw_read_lock(rwlock_t *lock);
extern int _raw_read_trylock(rwlock_t *lock);
extern void _raw_read_unlock(rwlock_t *lock);
extern void _raw_write_lock(rwlock_t *lock);
extern int _raw_write_trylock(rwlock_t *lock);
extern void _raw_write_unlock(rwlock_t *lock);
#else
# define _raw_spin_lock(lock) __raw_spin_lock(&(lock)->raw_lock)
# define _raw_spin_lock_flags(lock, flags) \
__raw_spin_lock_flags(&(lock)->raw_lock, *(flags))
# define _raw_spin_trylock(lock) __raw_spin_trylock(&(lock)->raw_lock)
# define _raw_spin_unlock(lock) __raw_spin_unlock(&(lock)->raw_lock)
# define _raw_read_lock(rwlock) __raw_read_lock(&(rwlock)->raw_lock)
# define _raw_read_trylock(rwlock) __raw_read_trylock(&(rwlock)->raw_lock)
# define _raw_read_unlock(rwlock) __raw_read_unlock(&(rwlock)->raw_lock)
# define _raw_write_lock(rwlock) __raw_write_lock(&(rwlock)->raw_lock)
# define _raw_write_trylock(rwlock) __raw_write_trylock(&(rwlock)->raw_lock)
# define _raw_write_unlock(rwlock) __raw_write_unlock(&(rwlock)->raw_lock)
#endif
#define read_can_lock(rwlock) __raw_read_can_lock(&(rwlock)->raw_lock)
#define write_can_lock(rwlock) __raw_write_can_lock(&(rwlock)->raw_lock)
/*
* Define the various spin_lock and rw_lock methods. Note we define these
* regardless of whether CONFIG_SMP or CONFIG_PREEMPT are set. The various
* methods are defined as nops in the case they are not required.
*/
#define spin_trylock(lock) __cond_lock(lock, _spin_trylock(lock))
#define read_trylock(lock) __cond_lock(lock, _read_trylock(lock))
#define write_trylock(lock) __cond_lock(lock, _write_trylock(lock))
#define spin_lock(lock) _spin_lock(lock)
#ifdef CONFIG_DEBUG_LOCK_ALLOC
# define spin_lock_nested(lock, subclass) _spin_lock_nested(lock, subclass)
#else
# define spin_lock_nested(lock, subclass) _spin_lock(lock)
#endif
#define write_lock(lock) _write_lock(lock)
#define read_lock(lock) _read_lock(lock)
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
#define spin_lock_irqsave(lock, flags) flags = _spin_lock_irqsave(lock)
#define read_lock_irqsave(lock, flags) flags = _read_lock_irqsave(lock)
#define write_lock_irqsave(lock, flags) flags = _write_lock_irqsave(lock)
#ifdef CONFIG_DEBUG_LOCK_ALLOC
#define spin_lock_irqsave_nested(lock, flags, subclass) \
flags = _spin_lock_irqsave_nested(lock, subclass)
#else
#define spin_lock_irqsave_nested(lock, flags, subclass) \
flags = _spin_lock_irqsave(lock)
#endif
#else
#define spin_lock_irqsave(lock, flags) _spin_lock_irqsave(lock, flags)
#define read_lock_irqsave(lock, flags) _read_lock_irqsave(lock, flags)
#define write_lock_irqsave(lock, flags) _write_lock_irqsave(lock, flags)
#define spin_lock_irqsave_nested(lock, flags, subclass) \
spin_lock_irqsave(lock, flags)
#endif
#define spin_lock_irq(lock) _spin_lock_irq(lock)
#define spin_lock_bh(lock) _spin_lock_bh(lock)
#define read_lock_irq(lock) _read_lock_irq(lock)
#define read_lock_bh(lock) _read_lock_bh(lock)
#define write_lock_irq(lock) _write_lock_irq(lock)
#define write_lock_bh(lock) _write_lock_bh(lock)
/*
* We inline the unlock functions in the nondebug case:
*/
#if defined(CONFIG_DEBUG_SPINLOCK) || defined(CONFIG_PREEMPT) || \
!defined(CONFIG_SMP)
# define spin_unlock(lock) _spin_unlock(lock)
# define read_unlock(lock) _read_unlock(lock)
# define write_unlock(lock) _write_unlock(lock)
# define spin_unlock_irq(lock) _spin_unlock_irq(lock)
# define read_unlock_irq(lock) _read_unlock_irq(lock)
# define write_unlock_irq(lock) _write_unlock_irq(lock)
#else
# define spin_unlock(lock) \
do {__raw_spin_unlock(&(lock)->raw_lock); __release(lock); } while (0)
# define read_unlock(lock) \
do {__raw_read_unlock(&(lock)->raw_lock); __release(lock); } while (0)
# define write_unlock(lock) \
do {__raw_write_unlock(&(lock)->raw_lock); __release(lock); } while (0)
# define spin_unlock_irq(lock) \
do { \
__raw_spin_unlock(&(lock)->raw_lock); \
__release(lock); \
local_irq_enable(); \
} while (0)
# define read_unlock_irq(lock) \
do { \
__raw_read_unlock(&(lock)->raw_lock); \
__release(lock); \
local_irq_enable(); \
} while (0)
# define write_unlock_irq(lock) \
do { \
__raw_write_unlock(&(lock)->raw_lock); \
__release(lock); \
local_irq_enable(); \
} while (0)
#endif
#define spin_unlock_irqrestore(lock, flags) \
_spin_unlock_irqrestore(lock, flags)
#define spin_unlock_bh(lock) _spin_unlock_bh(lock)
#define read_unlock_irqrestore(lock, flags) \
_read_unlock_irqrestore(lock, flags)
#define read_unlock_bh(lock) _read_unlock_bh(lock)
#define write_unlock_irqrestore(lock, flags) \
_write_unlock_irqrestore(lock, flags)
#define write_unlock_bh(lock) _write_unlock_bh(lock)
#define spin_trylock_bh(lock) __cond_lock(lock, _spin_trylock_bh(lock))
#define spin_trylock_irq(lock) \
({ \
local_irq_disable(); \
spin_trylock(lock) ? \
1 : ({ local_irq_enable(); 0; }); \
})
#define spin_trylock_irqsave(lock, flags) \
({ \
local_irq_save(flags); \
spin_trylock(lock) ? \
1 : ({ local_irq_restore(flags); 0; }); \
})
/*
* Locks two spinlocks l1 and l2.
* l1_first indicates if spinlock l1 should be taken first.
*/
static inline void double_spin_lock(spinlock_t *l1, spinlock_t *l2,
bool l1_first)
__acquires(l1)
__acquires(l2)
{
if (l1_first) {
spin_lock(l1);
spin_lock(l2);
} else {
spin_lock(l2);
spin_lock(l1);
}
}
/*
* Unlocks two spinlocks l1 and l2.
* l1_taken_first indicates if spinlock l1 was taken first and therefore
* should be released after spinlock l2.
*/
static inline void double_spin_unlock(spinlock_t *l1, spinlock_t *l2,
bool l1_taken_first)
__releases(l1)
__releases(l2)
{
if (l1_taken_first) {
spin_unlock(l2);
spin_unlock(l1);
} else {
spin_unlock(l1);
spin_unlock(l2);
}
}
/*
* Pull the atomic_t declaration:
* (asm-mips/atomic.h needs above definitions)
*/
#include <asm/atomic.h>
/**
* atomic_dec_and_lock - lock on reaching reference count zero
* @atomic: the atomic counter
* @lock: the spinlock in question
*/
extern int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock);
#define atomic_dec_and_lock(atomic, lock) \
__cond_lock(lock, _atomic_dec_and_lock(atomic, lock))
/**
* spin_can_lock - would spin_trylock() succeed?
* @lock: the spinlock in question.
*/
#define spin_can_lock(lock) (!spin_is_locked(lock))
#endif /* __LINUX_SPINLOCK_H */
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