arch/x86/xen/spinlock.c - kernel/msm-4.19 - Gitiles

 /*
  * Split spinlock implementation out into its own file, so it can be
  * compiled in a FTRACE-compatible way.
  */
 #include <linux/kernel_stat.h>
 #include <linux/spinlock.h>
 #include <linux/debugfs.h>
 #include <linux/log2.h>
 #include <linux/gfp.h>

 #include <asm/paravirt.h>

 #include <xen/interface/xen.h>
 #include <xen/events.h>

 #include "xen-ops.h"
 #include "debugfs.h"

 #ifdef CONFIG_XEN_DEBUG_FS
 static struct xen_spinlock_stats
 {
 	u64 taken;
 	u32 taken_slow;
 	u32 taken_slow_nested;
 	u32 taken_slow_pickup;
 	u32 taken_slow_spurious;
 	u32 taken_slow_irqenable;

 	u64 released;
 	u32 released_slow;
 	u32 released_slow_kicked;

 #define HISTO_BUCKETS	30
 	u32 histo_spin_total[HISTO_BUCKETS+1];
 	u32 histo_spin_spinning[HISTO_BUCKETS+1];
 	u32 histo_spin_blocked[HISTO_BUCKETS+1];

 	u64 time_total;
 	u64 time_spinning;
 	u64 time_blocked;
 } spinlock_stats;

 static u8 zero_stats;

 static unsigned lock_timeout = 1 << 10;
 #define TIMEOUT lock_timeout

 static inline void check_zero(void)
 {
 	if (unlikely(zero_stats)) {
 		memset(&spinlock_stats, 0, sizeof(spinlock_stats));
 		zero_stats = 0;
 	}
 }

 #define ADD_STATS(elem, val)			\
 	do { check_zero(); spinlock_stats.elem += (val); } while(0)

 static inline u64 spin_time_start(void)
 {
 	return xen_clocksource_read();
 }

 static void __spin_time_accum(u64 delta, u32 *array)
 {
 	unsigned index = ilog2(delta);

 	check_zero();

 	if (index < HISTO_BUCKETS)
 		array[index]++;
 	else
 		array[HISTO_BUCKETS]++;
 }

 static inline void spin_time_accum_spinning(u64 start)
 {
 	u32 delta = xen_clocksource_read() - start;

 	__spin_time_accum(delta, spinlock_stats.histo_spin_spinning);
 	spinlock_stats.time_spinning += delta;
 }

 static inline void spin_time_accum_total(u64 start)
 {
 	u32 delta = xen_clocksource_read() - start;

 	__spin_time_accum(delta, spinlock_stats.histo_spin_total);
 	spinlock_stats.time_total += delta;
 }

 static inline void spin_time_accum_blocked(u64 start)
 {
 	u32 delta = xen_clocksource_read() - start;

 	__spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
 	spinlock_stats.time_blocked += delta;
 }
 #else  /* !CONFIG_XEN_DEBUG_FS */
 #define TIMEOUT			(1 << 10)
 #define ADD_STATS(elem, val)	do { (void)(val); } while(0)

 static inline u64 spin_time_start(void)
 {
 	return 0;
 }

 static inline void spin_time_accum_total(u64 start)
 {
 }
 static inline void spin_time_accum_spinning(u64 start)
 {
 }
 static inline void spin_time_accum_blocked(u64 start)
 {
 }
 #endif  /* CONFIG_XEN_DEBUG_FS */

 /*
  * Size struct xen_spinlock so it's the same as arch_spinlock_t.
  */
 #if NR_CPUS < 256
 typedef u8 xen_spinners_t;
 # define inc_spinners(xl) \
 	asm(LOCK_PREFIX " incb %0" : "+m" ((xl)->spinners) : : "memory");
 # define dec_spinners(xl) \
 	asm(LOCK_PREFIX " decb %0" : "+m" ((xl)->spinners) : : "memory");
 #else
 typedef u16 xen_spinners_t;
 # define inc_spinners(xl) \
 	asm(LOCK_PREFIX " incw %0" : "+m" ((xl)->spinners) : : "memory");
 # define dec_spinners(xl) \
 	asm(LOCK_PREFIX " decw %0" : "+m" ((xl)->spinners) : : "memory");
 #endif

 struct xen_spinlock {
 	unsigned char lock;		/* 0 -> free; 1 -> locked */
 	xen_spinners_t spinners;	/* count of waiting cpus */
 };

 static int xen_spin_is_locked(struct arch_spinlock *lock)
 {
 	struct xen_spinlock *xl = (struct xen_spinlock *)lock;

 	return xl->lock != 0;
 }

 static int xen_spin_is_contended(struct arch_spinlock *lock)
 {
 	struct xen_spinlock *xl = (struct xen_spinlock *)lock;

 	/* Not strictly true; this is only the count of contended
 	   lock-takers entering the slow path. */
 	return xl->spinners != 0;
 }

 static int xen_spin_trylock(struct arch_spinlock *lock)
 {
 	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
 	u8 old = 1;

 	asm("xchgb %b0,%1"
 	    : "+q" (old), "+m" (xl->lock) : : "memory");

 	return old == 0;
 }

 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
 static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);

 /*
  * Mark a cpu as interested in a lock.  Returns the CPU's previous
  * lock of interest, in case we got preempted by an interrupt.
  */
 static inline struct xen_spinlock *spinning_lock(struct xen_spinlock *xl)
 {
 	struct xen_spinlock *prev;

 	prev = __this_cpu_read(lock_spinners);
 	__this_cpu_write(lock_spinners, xl);

 	wmb();			/* set lock of interest before count */

 	inc_spinners(xl);

 	return prev;
 }

 /*
  * Mark a cpu as no longer interested in a lock.  Restores previous
  * lock of interest (NULL for none).
  */
 static inline void unspinning_lock(struct xen_spinlock *xl, struct xen_spinlock *prev)
 {
 	dec_spinners(xl);
 	wmb();			/* decrement count before restoring lock */
 	__this_cpu_write(lock_spinners, prev);
 }

 static noinline int xen_spin_lock_slow(struct arch_spinlock *lock, bool irq_enable)
 {
 	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
 	struct xen_spinlock *prev;
 	int irq = __this_cpu_read(lock_kicker_irq);
 	int ret;
 	u64 start;

 	/* If kicker interrupts not initialized yet, just spin */
 	if (irq == -1)
 		return 0;

 	start = spin_time_start();

 	/* announce we're spinning */
 	prev = spinning_lock(xl);

 	ADD_STATS(taken_slow, 1);
 	ADD_STATS(taken_slow_nested, prev != NULL);

 	do {
 		unsigned long flags;

 		/* clear pending */
 		xen_clear_irq_pending(irq);

 		/* check again make sure it didn't become free while
 		   we weren't looking  */
 		ret = xen_spin_trylock(lock);
 		if (ret) {
 			ADD_STATS(taken_slow_pickup, 1);

 			/*
 			 * If we interrupted another spinlock while it
 			 * was blocking, make sure it doesn't block
 			 * without rechecking the lock.
 			 */
 			if (prev != NULL)
 				xen_set_irq_pending(irq);
 			goto out;
 		}

 		flags = arch_local_save_flags();
 		if (irq_enable) {
 			ADD_STATS(taken_slow_irqenable, 1);
 			raw_local_irq_enable();
 		}

 		/*
 		 * Block until irq becomes pending.  If we're
 		 * interrupted at this point (after the trylock but
 		 * before entering the block), then the nested lock
 		 * handler guarantees that the irq will be left
 		 * pending if there's any chance the lock became free;
 		 * xen_poll_irq() returns immediately if the irq is
 		 * pending.
 		 */
 		xen_poll_irq(irq);

 		raw_local_irq_restore(flags);

 		ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq));
 	} while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */

 	kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));

 out:
 	unspinning_lock(xl, prev);
 	spin_time_accum_blocked(start);

 	return ret;
 }

 static inline void __xen_spin_lock(struct arch_spinlock *lock, bool irq_enable)
 {
 	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
 	unsigned timeout;
 	u8 oldval;
 	u64 start_spin;

 	ADD_STATS(taken, 1);

 	start_spin = spin_time_start();

 	do {
 		u64 start_spin_fast = spin_time_start();

 		timeout = TIMEOUT;

 		asm("1: xchgb %1,%0\n"
 		    "   testb %1,%1\n"
 		    "   jz 3f\n"
 		    "2: rep;nop\n"
 		    "   cmpb $0,%0\n"
 		    "   je 1b\n"
 		    "   dec %2\n"
 		    "   jnz 2b\n"
 		    "3:\n"
 		    : "+m" (xl->lock), "=q" (oldval), "+r" (timeout)
 		    : "1" (1)
 		    : "memory");

 		spin_time_accum_spinning(start_spin_fast);

 	} while (unlikely(oldval != 0 &&
 			  (TIMEOUT == ~0 || !xen_spin_lock_slow(lock, irq_enable))));

 	spin_time_accum_total(start_spin);
 }

 static void xen_spin_lock(struct arch_spinlock *lock)
 {
 	__xen_spin_lock(lock, false);
 }

 static void xen_spin_lock_flags(struct arch_spinlock *lock, unsigned long flags)
 {
 	__xen_spin_lock(lock, !raw_irqs_disabled_flags(flags));
 }

 static noinline void xen_spin_unlock_slow(struct xen_spinlock *xl)
 {
 	int cpu;

 	ADD_STATS(released_slow, 1);

 	for_each_online_cpu(cpu) {
 		/* XXX should mix up next cpu selection */
 		if (per_cpu(lock_spinners, cpu) == xl) {
 			ADD_STATS(released_slow_kicked, 1);
 			xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
 		}
 	}
 }

 static void xen_spin_unlock(struct arch_spinlock *lock)
 {
 	struct xen_spinlock *xl = (struct xen_spinlock *)lock;

 	ADD_STATS(released, 1);

 	smp_wmb();		/* make sure no writes get moved after unlock */
 	xl->lock = 0;		/* release lock */

 	/*
 	 * Make sure unlock happens before checking for waiting
 	 * spinners.  We need a strong barrier to enforce the
 	 * write-read ordering to different memory locations, as the
 	 * CPU makes no implied guarantees about their ordering.
 	 */
 	mb();

 	if (unlikely(xl->spinners))
 		xen_spin_unlock_slow(xl);
 }

 static irqreturn_t dummy_handler(int irq, void *dev_id)
 {
 	BUG();
 	return IRQ_HANDLED;
 }

 void __cpuinit xen_init_lock_cpu(int cpu)
 {
 	int irq;
 	const char *name;

 	WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
 	     cpu, per_cpu(lock_kicker_irq, cpu));

 	/*
 	 * See git commit f10cd522c5fbfec9ae3cc01967868c9c2401ed23
 	 * (xen: disable PV spinlocks on HVM)
 	 */
 	if (xen_hvm_domain())
 		return;

 	name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
 	irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
 				     cpu,
 				     dummy_handler,
 				     IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
 				     name,
 				     NULL);

 	if (irq >= 0) {
 		disable_irq(irq); /* make sure it's never delivered */
 		per_cpu(lock_kicker_irq, cpu) = irq;
 	}

 	printk("cpu %d spinlock event irq %d\n", cpu, irq);
 }

 void xen_uninit_lock_cpu(int cpu)
 {
 	/*
 	 * See git commit f10cd522c5fbfec9ae3cc01967868c9c2401ed23
 	 * (xen: disable PV spinlocks on HVM)
 	 */
 	if (xen_hvm_domain())
 		return;

 	unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
 	per_cpu(lock_kicker_irq, cpu) = -1;
 }

 void __init xen_init_spinlocks(void)
 {
 	/*
 	 * See git commit f10cd522c5fbfec9ae3cc01967868c9c2401ed23
 	 * (xen: disable PV spinlocks on HVM)
 	 */
 	if (xen_hvm_domain())
 		return;

 	BUILD_BUG_ON(sizeof(struct xen_spinlock) > sizeof(arch_spinlock_t));

 	pv_lock_ops.spin_is_locked = xen_spin_is_locked;
 	pv_lock_ops.spin_is_contended = xen_spin_is_contended;
 	pv_lock_ops.spin_lock = xen_spin_lock;
 	pv_lock_ops.spin_lock_flags = xen_spin_lock_flags;
 	pv_lock_ops.spin_trylock = xen_spin_trylock;
 	pv_lock_ops.spin_unlock = xen_spin_unlock;
 }

 #ifdef CONFIG_XEN_DEBUG_FS

 static struct dentry *d_spin_debug;

 static int __init xen_spinlock_debugfs(void)
 {
 	struct dentry *d_xen = xen_init_debugfs();

 	if (d_xen == NULL)
 		return -ENOMEM;

 	d_spin_debug = debugfs_create_dir("spinlocks", d_xen);

 	debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);

 	debugfs_create_u32("timeout", 0644, d_spin_debug, &lock_timeout);

 	debugfs_create_u64("taken", 0444, d_spin_debug, &spinlock_stats.taken);
 	debugfs_create_u32("taken_slow", 0444, d_spin_debug,
 			   &spinlock_stats.taken_slow);
 	debugfs_create_u32("taken_slow_nested", 0444, d_spin_debug,
 			   &spinlock_stats.taken_slow_nested);
 	debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
 			   &spinlock_stats.taken_slow_pickup);
 	debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
 			   &spinlock_stats.taken_slow_spurious);
 	debugfs_create_u32("taken_slow_irqenable", 0444, d_spin_debug,
 			   &spinlock_stats.taken_slow_irqenable);

 	debugfs_create_u64("released", 0444, d_spin_debug, &spinlock_stats.released);
 	debugfs_create_u32("released_slow", 0444, d_spin_debug,
 			   &spinlock_stats.released_slow);
 	debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
 			   &spinlock_stats.released_slow_kicked);

 	debugfs_create_u64("time_spinning", 0444, d_spin_debug,
 			   &spinlock_stats.time_spinning);
 	debugfs_create_u64("time_blocked", 0444, d_spin_debug,
 			   &spinlock_stats.time_blocked);
 	debugfs_create_u64("time_total", 0444, d_spin_debug,
 			   &spinlock_stats.time_total);

 	debugfs_create_u32_array("histo_total", 0444, d_spin_debug,
 				spinlock_stats.histo_spin_total, HISTO_BUCKETS + 1);
 	debugfs_create_u32_array("histo_spinning", 0444, d_spin_debug,
 				spinlock_stats.histo_spin_spinning, HISTO_BUCKETS + 1);
 	debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
 				spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);

 	return 0;
 }
 fs_initcall(xen_spinlock_debugfs);

 #endif	/* CONFIG_XEN_DEBUG_FS */
	/*
	* Split spinlock implementation out into its own file, so it can be
	* compiled in a FTRACE-compatible way.
	*/
	#include <linux/kernel_stat.h>
	#include <linux/spinlock.h>
	#include <linux/debugfs.h>
	#include <linux/log2.h>
	#include <linux/gfp.h>

	#include <asm/paravirt.h>

	#include <xen/interface/xen.h>
	#include <xen/events.h>

	#include "xen-ops.h"
	#include "debugfs.h"

	#ifdef CONFIG_XEN_DEBUG_FS
	static struct xen_spinlock_stats
	{
	u64 taken;
	u32 taken_slow;
	u32 taken_slow_nested;
	u32 taken_slow_pickup;
	u32 taken_slow_spurious;
	u32 taken_slow_irqenable;

	u64 released;
	u32 released_slow;
	u32 released_slow_kicked;

	#define HISTO_BUCKETS 30
	u32 histo_spin_total[HISTO_BUCKETS+1];
	u32 histo_spin_spinning[HISTO_BUCKETS+1];
	u32 histo_spin_blocked[HISTO_BUCKETS+1];

	u64 time_total;
	u64 time_spinning;
	u64 time_blocked;
	} spinlock_stats;

	static u8 zero_stats;

	static unsigned lock_timeout = 1 << 10;
	#define TIMEOUT lock_timeout

	static inline void check_zero(void)
	{
	if (unlikely(zero_stats)) {
	memset(&spinlock_stats, 0, sizeof(spinlock_stats));
	zero_stats = 0;
	}
	}

	#define ADD_STATS(elem, val) \
	do { check_zero(); spinlock_stats.elem += (val); } while(0)

	static inline u64 spin_time_start(void)
	{
	return xen_clocksource_read();
	}

	static void __spin_time_accum(u64 delta, u32 *array)
	{
	unsigned index = ilog2(delta);

	check_zero();

	if (index < HISTO_BUCKETS)
	array[index]++;
	else
	array[HISTO_BUCKETS]++;
	}

	static inline void spin_time_accum_spinning(u64 start)
	{
	u32 delta = xen_clocksource_read() - start;

	__spin_time_accum(delta, spinlock_stats.histo_spin_spinning);
	spinlock_stats.time_spinning += delta;
	}

	static inline void spin_time_accum_total(u64 start)
	{
	u32 delta = xen_clocksource_read() - start;

	__spin_time_accum(delta, spinlock_stats.histo_spin_total);
	spinlock_stats.time_total += delta;
	}

	static inline void spin_time_accum_blocked(u64 start)
	{
	u32 delta = xen_clocksource_read() - start;

	__spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
	spinlock_stats.time_blocked += delta;
	}
	#else /* !CONFIG_XEN_DEBUG_FS */
	#define TIMEOUT (1 << 10)
	#define ADD_STATS(elem, val) do { (void)(val); } while(0)

	static inline u64 spin_time_start(void)
	{
	return 0;
	}

	static inline void spin_time_accum_total(u64 start)
	{
	}
	static inline void spin_time_accum_spinning(u64 start)
	{
	}
	static inline void spin_time_accum_blocked(u64 start)
	{
	}
	#endif /* CONFIG_XEN_DEBUG_FS */

	/*
	* Size struct xen_spinlock so it's the same as arch_spinlock_t.
	*/
	#if NR_CPUS < 256
	typedef u8 xen_spinners_t;
	# define inc_spinners(xl) \
	asm(LOCK_PREFIX " incb %0" : "+m" ((xl)->spinners) : : "memory");
	# define dec_spinners(xl) \
	asm(LOCK_PREFIX " decb %0" : "+m" ((xl)->spinners) : : "memory");
	#else
	typedef u16 xen_spinners_t;
	# define inc_spinners(xl) \
	asm(LOCK_PREFIX " incw %0" : "+m" ((xl)->spinners) : : "memory");
	# define dec_spinners(xl) \
	asm(LOCK_PREFIX " decw %0" : "+m" ((xl)->spinners) : : "memory");
	#endif

	struct xen_spinlock {
	unsigned char lock; /* 0 -> free; 1 -> locked */
	xen_spinners_t spinners; /* count of waiting cpus */
	};

	static int xen_spin_is_locked(struct arch_spinlock *lock)
	{
	struct xen_spinlock xl = (struct xen_spinlock )lock;

	return xl->lock != 0;
	}

	static int xen_spin_is_contended(struct arch_spinlock *lock)
	{
	struct xen_spinlock xl = (struct xen_spinlock )lock;

	/* Not strictly true; this is only the count of contended
	lock-takers entering the slow path. */
	return xl->spinners != 0;
	}

	static int xen_spin_trylock(struct arch_spinlock *lock)
	{
	struct xen_spinlock xl = (struct xen_spinlock )lock;
	u8 old = 1;

	asm("xchgb %b0,%1"
	: "+q" (old), "+m" (xl->lock) : : "memory");

	return old == 0;
	}

	static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
	static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);

	/*
	* Mark a cpu as interested in a lock. Returns the CPU's previous
	* lock of interest, in case we got preempted by an interrupt.
	*/
	static inline struct xen_spinlock spinning_lock(struct xen_spinlock xl)
	{
	struct xen_spinlock *prev;

	prev = __this_cpu_read(lock_spinners);
	__this_cpu_write(lock_spinners, xl);

	wmb(); /* set lock of interest before count */

	inc_spinners(xl);

	return prev;
	}

	/*
	* Mark a cpu as no longer interested in a lock. Restores previous
	* lock of interest (NULL for none).
	*/
	static inline void unspinning_lock(struct xen_spinlock xl, struct xen_spinlock prev)
	{
	dec_spinners(xl);
	wmb(); /* decrement count before restoring lock */
	__this_cpu_write(lock_spinners, prev);
	}

	static noinline int xen_spin_lock_slow(struct arch_spinlock *lock, bool irq_enable)
	{
	struct xen_spinlock xl = (struct xen_spinlock )lock;
	struct xen_spinlock *prev;
	int irq = __this_cpu_read(lock_kicker_irq);
	int ret;
	u64 start;

	/* If kicker interrupts not initialized yet, just spin */
	if (irq == -1)
	return 0;

	start = spin_time_start();

	/* announce we're spinning */
	prev = spinning_lock(xl);

	ADD_STATS(taken_slow, 1);
	ADD_STATS(taken_slow_nested, prev != NULL);

	do {
	unsigned long flags;

	/* clear pending */
	xen_clear_irq_pending(irq);

	/* check again make sure it didn't become free while
	we weren't looking */
	ret = xen_spin_trylock(lock);
	if (ret) {
	ADD_STATS(taken_slow_pickup, 1);

	/*
	* If we interrupted another spinlock while it
	* was blocking, make sure it doesn't block
	* without rechecking the lock.
	*/
	if (prev != NULL)
	xen_set_irq_pending(irq);
	goto out;
	}

	flags = arch_local_save_flags();
	if (irq_enable) {
	ADD_STATS(taken_slow_irqenable, 1);
	raw_local_irq_enable();
	}

	/*
	* Block until irq becomes pending. If we're
	* interrupted at this point (after the trylock but
	* before entering the block), then the nested lock
	* handler guarantees that the irq will be left
	* pending if there's any chance the lock became free;
	* xen_poll_irq() returns immediately if the irq is
	* pending.
	*/
	xen_poll_irq(irq);

	raw_local_irq_restore(flags);

	ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq));
	} while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */

	kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));

	out:
	unspinning_lock(xl, prev);
	spin_time_accum_blocked(start);

	return ret;
	}

	static inline void __xen_spin_lock(struct arch_spinlock *lock, bool irq_enable)
	{
	struct xen_spinlock xl = (struct xen_spinlock )lock;
	unsigned timeout;
	u8 oldval;
	u64 start_spin;

	ADD_STATS(taken, 1);

	start_spin = spin_time_start();

	do {
	u64 start_spin_fast = spin_time_start();

	timeout = TIMEOUT;

	asm("1: xchgb %1,%0\n"
	" testb %1,%1\n"
	" jz 3f\n"
	"2: rep;nop\n"
	" cmpb $0,%0\n"
	" je 1b\n"
	" dec %2\n"
	" jnz 2b\n"
	"3:\n"
	: "+m" (xl->lock), "=q" (oldval), "+r" (timeout)
	: "1" (1)
	: "memory");

	spin_time_accum_spinning(start_spin_fast);

	} while (unlikely(oldval != 0 &&
	(TIMEOUT == ~0 \|\| !xen_spin_lock_slow(lock, irq_enable))));

	spin_time_accum_total(start_spin);
	}

	static void xen_spin_lock(struct arch_spinlock *lock)
	{
	__xen_spin_lock(lock, false);
	}

	static void xen_spin_lock_flags(struct arch_spinlock *lock, unsigned long flags)
	{
	__xen_spin_lock(lock, !raw_irqs_disabled_flags(flags));
	}

	static noinline void xen_spin_unlock_slow(struct xen_spinlock *xl)
	{
	int cpu;

	ADD_STATS(released_slow, 1);

	for_each_online_cpu(cpu) {
	/* XXX should mix up next cpu selection */
	if (per_cpu(lock_spinners, cpu) == xl) {
	ADD_STATS(released_slow_kicked, 1);
	xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
	}
	}
	}

	static void xen_spin_unlock(struct arch_spinlock *lock)
	{
	struct xen_spinlock xl = (struct xen_spinlock )lock;

	ADD_STATS(released, 1);

	smp_wmb(); /* make sure no writes get moved after unlock */
	xl->lock = 0; /* release lock */

	/*
	* Make sure unlock happens before checking for waiting
	* spinners. We need a strong barrier to enforce the
	* write-read ordering to different memory locations, as the
	* CPU makes no implied guarantees about their ordering.
	*/
	mb();

	if (unlikely(xl->spinners))
	xen_spin_unlock_slow(xl);
	}

	static irqreturn_t dummy_handler(int irq, void *dev_id)
	{
	BUG();
	return IRQ_HANDLED;
	}

	void __cpuinit xen_init_lock_cpu(int cpu)
	{
	int irq;
	const char *name;

	WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
	cpu, per_cpu(lock_kicker_irq, cpu));

	/*
	* See git commit f10cd522c5fbfec9ae3cc01967868c9c2401ed23
	* (xen: disable PV spinlocks on HVM)
	*/
	if (xen_hvm_domain())
	return;

	name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
	irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
	cpu,
	dummy_handler,
	IRQF_DISABLED\|IRQF_PERCPU\|IRQF_NOBALANCING,
	name,
	NULL);

	if (irq >= 0) {
	disable_irq(irq); /* make sure it's never delivered */
	per_cpu(lock_kicker_irq, cpu) = irq;
	}

	printk("cpu %d spinlock event irq %d\n", cpu, irq);
	}

	void xen_uninit_lock_cpu(int cpu)
	{
	/*
	* See git commit f10cd522c5fbfec9ae3cc01967868c9c2401ed23
	* (xen: disable PV spinlocks on HVM)
	*/
	if (xen_hvm_domain())
	return;

	unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
	per_cpu(lock_kicker_irq, cpu) = -1;
	}

	void __init xen_init_spinlocks(void)
	{
	/*
	* See git commit f10cd522c5fbfec9ae3cc01967868c9c2401ed23
	* (xen: disable PV spinlocks on HVM)
	*/
	if (xen_hvm_domain())
	return;

	BUILD_BUG_ON(sizeof(struct xen_spinlock) > sizeof(arch_spinlock_t));

	pv_lock_ops.spin_is_locked = xen_spin_is_locked;
	pv_lock_ops.spin_is_contended = xen_spin_is_contended;
	pv_lock_ops.spin_lock = xen_spin_lock;
	pv_lock_ops.spin_lock_flags = xen_spin_lock_flags;
	pv_lock_ops.spin_trylock = xen_spin_trylock;
	pv_lock_ops.spin_unlock = xen_spin_unlock;
	}

	#ifdef CONFIG_XEN_DEBUG_FS

	static struct dentry *d_spin_debug;

	static int __init xen_spinlock_debugfs(void)
	{
	struct dentry *d_xen = xen_init_debugfs();

	if (d_xen == NULL)
	return -ENOMEM;

	d_spin_debug = debugfs_create_dir("spinlocks", d_xen);

	debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);

	debugfs_create_u32("timeout", 0644, d_spin_debug, &lock_timeout);

	debugfs_create_u64("taken", 0444, d_spin_debug, &spinlock_stats.taken);
	debugfs_create_u32("taken_slow", 0444, d_spin_debug,
	&spinlock_stats.taken_slow);
	debugfs_create_u32("taken_slow_nested", 0444, d_spin_debug,
	&spinlock_stats.taken_slow_nested);
	debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
	&spinlock_stats.taken_slow_pickup);
	debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
	&spinlock_stats.taken_slow_spurious);
	debugfs_create_u32("taken_slow_irqenable", 0444, d_spin_debug,
	&spinlock_stats.taken_slow_irqenable);

	debugfs_create_u64("released", 0444, d_spin_debug, &spinlock_stats.released);
	debugfs_create_u32("released_slow", 0444, d_spin_debug,
	&spinlock_stats.released_slow);
	debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
	&spinlock_stats.released_slow_kicked);

	debugfs_create_u64("time_spinning", 0444, d_spin_debug,
	&spinlock_stats.time_spinning);
	debugfs_create_u64("time_blocked", 0444, d_spin_debug,
	&spinlock_stats.time_blocked);
	debugfs_create_u64("time_total", 0444, d_spin_debug,
	&spinlock_stats.time_total);

	debugfs_create_u32_array("histo_total", 0444, d_spin_debug,
	spinlock_stats.histo_spin_total, HISTO_BUCKETS + 1);
	debugfs_create_u32_array("histo_spinning", 0444, d_spin_debug,
	spinlock_stats.histo_spin_spinning, HISTO_BUCKETS + 1);
	debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
	spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);

	return 0;
	}
	fs_initcall(xen_spinlock_debugfs);

	#endif /* CONFIG_XEN_DEBUG_FS */