/* * Queued spinlock * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P. * (C) Copyright 2013-2014 Red Hat, Inc. * (C) Copyright 2015 Intel Corp. * * Authors: Waiman Long <waiman.long@hp.com> * Peter Zijlstra <peterz@infradead.org> */ #ifndef _GEN_PV_LOCK_SLOWPATH #include <linux/smp.h>#include <linux/bug.h>#include <linux/cpumask.h>#include <linux/percpu.h>#include <linux/hardirq.h>#include <linux/mutex.h>#include <asm/byteorder.h>#include <asm/qspinlock.h> /* * The basic principle of a queue-based spinlock can best be understood * by studying a classic queue-based spinlock implementation called the * MCS lock. The paper below provides a good description for this kind * of lock. * * http://www.cise.ufl.edu/tr/DOC/REP-1992-71.pdf * * This queued spinlock implementation is based on the MCS lock, however to make * it fit the 4 bytes we assume spinlock_t to be, and preserve its existing * API, we must modify it somehow. * * In particular; where the traditional MCS lock consists of a tail pointer * (8 bytes) and needs the next pointer (another 8 bytes) of its own node to * unlock the next pending (next->locked), we compress both these: {tail, * next->locked} into a single u32 value. * * Since a spinlock disables recursion of its own context and there is a limit * to the contexts that can nest; namely: task, softirq, hardirq, nmi. As there * are at most 4 nesting levels, it can be encoded by a 2-bit number. Now * we can encode the tail by combining the 2-bit nesting level with the cpu * number. With one byte for the lock value and 3 bytes for the tail, only a * 32-bit word is now needed. Even though we only need 1 bit for the lock, * we extend it to a full byte to achieve better performance for architectures * that support atomic byte write. * * We also change the first spinner to spin on the lock bit instead of its * node; whereby avoiding the need to carry a node from lock to unlock, and * preserving existing lock API. This also makes the unlock code simpler and * faster. * * N.B. The current implementation only supports architectures that allow * atomic operations on smaller 8-bit and 16-bit data types. * */ #include "mcs_spinlock.h" #ifdef CONFIG_PARAVIRT_SPINLOCKS#define MAX_NODES 8#else#define MAX_NODES 4#endif /* * Per-CPU queue node structures; we can never have more than 4 nested * contexts: task, softirq, hardirq, nmi. * * Exactly fits one 64-byte cacheline on a 64-bit architecture. * * PV doubles the storage and uses the second cacheline for PV state. */static DEFINE_PER_CPU_ALIGNED(struct mcs_spinlock, mcs_nodes[MAX_NODES]); /* * We must be able to distinguish between no-tail and the tail at 0:0, * therefore increment the cpu number by one. */ static inline u32 encode_tail(int cpu, int idx){ u32 tail; #ifdef CONFIG_DEBUG_SPINLOCK BUG_ON(idx > 3);#endif tail = (cpu + 1) << _Q_TAIL_CPU_OFFSET; tail |= idx << _Q_TAIL_IDX_OFFSET; /* assume < 4 */ return tail;} static inline struct mcs_spinlock *decode_tail(u32 tail){ int cpu = (tail >> _Q_TAIL_CPU_OFFSET) - 1; int idx = (tail & _Q_TAIL_IDX_MASK) >> _Q_TAIL_IDX_OFFSET; return per_cpu_ptr(&mcs_nodes[idx], cpu);} #define _Q_LOCKED_PENDING_MASK (_Q_LOCKED_MASK | _Q_PENDING_MASK) /* * By using the whole 2nd least significant byte for the pending bit, we * can allow better optimization of the lock acquisition for the pending * bit holder. * * This internal structure is also used by the set_locked function which * is not restricted to _Q_PENDING_BITS == 8. */struct __qspinlock { union { atomic_t val;#ifdef __LITTLE_ENDIAN struct { u8 locked; u8 pending; }; struct { u16 locked_pending; u16 tail; };#else struct { u16 tail; u16 locked_pending; }; struct { u8 reserved[2]; u8 pending; u8 locked; };#endif };}; #if _Q_PENDING_BITS == 8/** * clear_pending_set_locked - take ownership and clear the pending bit. * @lock: Pointer to queued spinlock structure * * *,1,0 -> *,0,1 * * Lock stealing is not allowed if this function is used. */static __always_inline void clear_pending_set_locked(struct qspinlock *lock){ struct __qspinlock *l = (void *)lock; WRITE_ONCE(l->locked_pending, _Q_LOCKED_VAL);} /* * xchg_tail - Put in the new queue tail code word & retrieve previous one * @lock : Pointer to queued spinlock structure * @tail : The new queue tail code word * Return: The previous queue tail code word * * xchg(lock, tail) * * p,*,* -> n,*,* ; prev = xchg(lock, node) */static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail){ struct __qspinlock *l = (void *)lock; return (u32)xchg(&l->tail, tail >> _Q_TAIL_OFFSET) << _Q_TAIL_OFFSET;} #else /* _Q_PENDING_BITS == 8 */ /** * clear_pending_set_locked - take ownership and clear the pending bit. * @lock: Pointer to queued spinlock structure * * *,1,0 -> *,0,1 */static __always_inline void clear_pending_set_locked(struct qspinlock *lock){ atomic_add(-_Q_PENDING_VAL + _Q_LOCKED_VAL, &lock->val);} /** * xchg_tail - Put in the new queue tail code word & retrieve previous one * @lock : Pointer to queued spinlock structure * @tail : The new queue tail code word * Return: The previous queue tail code word * * xchg(lock, tail) * * p,*,* -> n,*,* ; prev = xchg(lock, node) */static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail){ u32 old, new, val = atomic_read(&lock->val); for (;;) { new = (val & _Q_LOCKED_PENDING_MASK) | tail; old = atomic_cmpxchg(&lock->val, val, new); if (old == val) break; val = old; } return old;}#endif /* _Q_PENDING_BITS == 8 */ /** * set_locked - Set the lock bit and own the lock * @lock: Pointer to queued spinlock structure * * *,*,0 -> *,0,1 */static __always_inline void set_locked(struct qspinlock *lock){ struct __qspinlock *l = (void *)lock; WRITE_ONCE(l->locked, _Q_LOCKED_VAL);} /* * Generate the native code for queued_spin_unlock_slowpath(); provide NOPs for * all the PV callbacks. */ static __always_inline void __pv_init_node(struct mcs_spinlock *node) { }static __always_inline void __pv_wait_node(struct mcs_spinlock *node) { }static __always_inline void __pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node) { }static __always_inline void __pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node) { } #define pv_enabled() false #define pv_init_node __pv_init_node#define pv_wait_node __pv_wait_node#define pv_kick_node __pv_kick_node#define pv_wait_head __pv_wait_head #ifdef CONFIG_PARAVIRT_SPINLOCKS#define queued_spin_lock_slowpath native_queued_spin_lock_slowpath#endif #endif /* _GEN_PV_LOCK_SLOWPATH */ /** * queued_spin_lock_slowpath - acquire the queued spinlock * @lock: Pointer to queued spinlock structure * @val: Current value of the queued spinlock 32-bit word * * (queue tail, pending bit, lock value) * * fast : slow : unlock * : : * uncontended (0,0,0) -:--> (0,0,1) ------------------------------:--> (*,*,0) * : | ^--------.------. / : * : v \ \ | : * pending : (0,1,1) +--> (0,1,0) \ | : * : | ^--' | | : * : v | | : * uncontended : (n,x,y) +--> (n,0,0) --' | : * queue : | ^--' | : * : v | : * contended : (*,x,y) +--> (*,0,0) ---> (*,0,1) -' : * queue : ^--' : */void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val){ struct mcs_spinlock *prev, *next, *node; u32 new, old, tail; int idx; BUILD_BUG_ON(CONFIG_NR_CPUS >= (1U << _Q_TAIL_CPU_BITS)); if (pv_enabled()) goto queue; if (virt_spin_lock(lock)) return; /* * wait for in-progress pending->locked hand-overs * * 0,1,0 -> 0,0,1 */ if (val == _Q_PENDING_VAL) { while ((val = atomic_read(&lock->val)) == _Q_PENDING_VAL) cpu_relax(); } /* * trylock || pending * * 0,0,0 -> 0,0,1 ; trylock * 0,0,1 -> 0,1,1 ; pending */ for (;;) { /* * If we observe any contention; queue. */ if (val & ~_Q_LOCKED_MASK) goto queue; new = _Q_LOCKED_VAL; if (val == new) new |= _Q_PENDING_VAL; old = atomic_cmpxchg(&lock->val, val, new); if (old == val) break; val = old; } /* * we won the trylock */ if (new == _Q_LOCKED_VAL) return; /* * we're pending, wait for the owner to go away. * * *,1,1 -> *,1,0 * * this wait loop must be a load-acquire such that we match the * store-release that clears the locked bit and create lock * sequentiality; this is because not all clear_pending_set_locked() * implementations imply full barriers. */ while ((val = smp_load_acquire(&lock->val.counter)) & _Q_LOCKED_MASK) cpu_relax(); /* * take ownership and clear the pending bit. * * *,1,0 -> *,0,1 */ clear_pending_set_locked(lock); return; /* * End of pending bit optimistic spinning and beginning of MCS * queuing. */queue: node = this_cpu_ptr(&mcs_nodes[0]); idx = node->count++; tail = encode_tail(smp_processor_id(), idx); node += idx; node->locked = 0; node->next = NULL; pv_init_node(node); /* * We touched a (possibly) cold cacheline in the per-cpu queue node; * attempt the trylock once more in the hope someone let go while we * weren't watching. */ if (queued_spin_trylock(lock)) goto release; /* * We have already touched the queueing cacheline; don't bother with * pending stuff. * * p,*,* -> n,*,* */ old = xchg_tail(lock, tail); /* * if there was a previous node; link it and wait until reaching the * head of the waitqueue. */ if (old & _Q_TAIL_MASK) { prev = decode_tail(old); WRITE_ONCE(prev->next, node); pv_wait_node(node); arch_mcs_spin_lock_contended(&node->locked); } /* * we're at the head of the waitqueue, wait for the owner & pending to * go away. * * *,x,y -> *,0,0 * * this wait loop must use a load-acquire such that we match the * store-release that clears the locked bit and create lock * sequentiality; this is because the set_locked() function below * does not imply a full barrier. * */ pv_wait_head(lock, node); while ((val = smp_load_acquire(&lock->val.counter)) & _Q_LOCKED_PENDING_MASK) cpu_relax(); /* * claim the lock: * * n,0,0 -> 0,0,1 : lock, uncontended * *,0,0 -> *,0,1 : lock, contended * * If the queue head is the only one in the queue (lock value == tail), * clear the tail code and grab the lock. Otherwise, we only need * to grab the lock. */ for (;;) { if (val != tail) { set_locked(lock); break; } old = atomic_cmpxchg(&lock->val, val, _Q_LOCKED_VAL); if (old == val) goto release; /* No contention */ val = old; } /* * contended path; wait for next, release. */ while (!(next = READ_ONCE(node->next))) cpu_relax(); arch_mcs_spin_unlock_contended(&next->locked); pv_kick_node(lock, next); release: /* * release the node */ this_cpu_dec(mcs_nodes[0].count);}EXPORT_SYMBOL(queued_spin_lock_slowpath); /* * Generate the paravirt code for queued_spin_unlock_slowpath(). */#if !defined(_GEN_PV_LOCK_SLOWPATH) && defined(CONFIG_PARAVIRT_SPINLOCKS)#define _GEN_PV_LOCK_SLOWPATH #undef pv_enabled#define pv_enabled() true #undef pv_init_node#undef pv_wait_node#undef pv_kick_node#undef pv_wait_head #undef queued_spin_lock_slowpath#define queued_spin_lock_slowpath __pv_queued_spin_lock_slowpath #include "qspinlock_paravirt.h"#include "qspinlock.c" #endif
/*
* Queued spinlock
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P.
* (C) Copyright 2013-2014 Red Hat, Inc.
* (C) Copyright 2015 Intel Corp.
*
* Authors: Waiman Long <waiman.long@hp.com>
* Peter Zijlstra <peterz@infradead.org>
*/
#ifndef _GEN_PV_LOCK_SLOWPATH
#include <linux/smp.h>
#include <linux/bug.h>
#include <linux/cpumask.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/mutex.h>
#include <asm/byteorder.h>
#include <asm/qspinlock.h>
/*
* The basic principle of a queue-based spinlock can best be understood
* by studying a classic queue-based spinlock implementation called the
* MCS lock. The paper below provides a good description for this kind
* of lock.
*
* http://www.cise.ufl.edu/tr/DOC/REP-1992-71.pdf
*
* This queued spinlock implementation is based on the MCS lock, however to make
* it fit the 4 bytes we assume spinlock_t to be, and preserve its existing
* API, we must modify it somehow.
*
* In particular; where the traditional MCS lock consists of a tail pointer
* (8 bytes) and needs the next pointer (another 8 bytes) of its own node to
* unlock the next pending (next->locked), we compress both these: {tail,
* next->locked} into a single u32 value.
*
* Since a spinlock disables recursion of its own context and there is a limit
* to the contexts that can nest; namely: task, softirq, hardirq, nmi. As there
* are at most 4 nesting levels, it can be encoded by a 2-bit number. Now
* we can encode the tail by combining the 2-bit nesting level with the cpu
* number. With one byte for the lock value and 3 bytes for the tail, only a
* 32-bit word is now needed. Even though we only need 1 bit for the lock,
* we extend it to a full byte to achieve better performance for architectures
* that support atomic byte write.
*
* We also change the first spinner to spin on the lock bit instead of its
* node; whereby avoiding the need to carry a node from lock to unlock, and
* preserving existing lock API. This also makes the unlock code simpler and
* faster.
*
* N.B. The current implementation only supports architectures that allow
* atomic operations on smaller 8-bit and 16-bit data types.
*
*/
#include "mcs_spinlock.h"
#ifdef CONFIG_PARAVIRT_SPINLOCKS
#define MAX_NODES 8
#else
#define MAX_NODES 4
#endif
/*
* Per-CPU queue node structures; we can never have more than 4 nested
* contexts: task, softirq, hardirq, nmi.
*
* Exactly fits one 64-byte cacheline on a 64-bit architecture.
*
* PV doubles the storage and uses the second cacheline for PV state.
*/
static DEFINE_PER_CPU_ALIGNED(struct mcs_spinlock, mcs_nodes[MAX_NODES]);
/*
* We must be able to distinguish between no-tail and the tail at 0:0,
* therefore increment the cpu number by one.
*/
static inline u32 encode_tail(int cpu, int idx)
{
u32 tail;
#ifdef CONFIG_DEBUG_SPINLOCK
BUG_ON(idx > 3);
#endif
tail = (cpu + 1) << _Q_TAIL_CPU_OFFSET;
tail |= idx << _Q_TAIL_IDX_OFFSET; /* assume < 4 */
return tail;
}
static inline struct mcs_spinlock *decode_tail(u32 tail)
{
int cpu = (tail >> _Q_TAIL_CPU_OFFSET) - 1;
int idx = (tail & _Q_TAIL_IDX_MASK) >> _Q_TAIL_IDX_OFFSET;
return per_cpu_ptr(&mcs_nodes[idx], cpu);
}
#define _Q_LOCKED_PENDING_MASK (_Q_LOCKED_MASK | _Q_PENDING_MASK)
/*
* By using the whole 2nd least significant byte for the pending bit, we
* can allow better optimization of the lock acquisition for the pending
* bit holder.
*
* This internal structure is also used by the set_locked function which
* is not restricted to _Q_PENDING_BITS == 8.
*/
struct __qspinlock {
union {
atomic_t val;
#ifdef __LITTLE_ENDIAN
struct {
u8 locked;
u8 pending;
};
struct {
u16 locked_pending;
u16 tail;
};
#else
struct {
u16 tail;
u16 locked_pending;
};
struct {
u8 reserved[2];
u8 pending;
u8 locked;
};
#endif
};
};
#if _Q_PENDING_BITS == 8
/**
* clear_pending_set_locked - take ownership and clear the pending bit.
* @lock: Pointer to queued spinlock structure
*
* *,1,0 -> *,0,1
*
* Lock stealing is not allowed if this function is used.
*/
static __always_inline void clear_pending_set_locked(struct qspinlock *lock)
{
struct __qspinlock *l = (void *)lock;
WRITE_ONCE(l->locked_pending, _Q_LOCKED_VAL);
}
/*
* xchg_tail - Put in the new queue tail code word & retrieve previous one
* @lock : Pointer to queued spinlock structure
* @tail : The new queue tail code word
* Return: The previous queue tail code word
*
* xchg(lock, tail)
*
* p,*,* -> n,*,* ; prev = xchg(lock, node)
*/
static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)
{
struct __qspinlock *l = (void *)lock;
return (u32)xchg(&l->tail, tail >> _Q_TAIL_OFFSET) << _Q_TAIL_OFFSET;
}
#else /* _Q_PENDING_BITS == 8 */
/**
* clear_pending_set_locked - take ownership and clear the pending bit.
* @lock: Pointer to queued spinlock structure
*
* *,1,0 -> *,0,1
*/
static __always_inline void clear_pending_set_locked(struct qspinlock *lock)
{
atomic_add(-_Q_PENDING_VAL + _Q_LOCKED_VAL, &lock->val);
}
/**
* xchg_tail - Put in the new queue tail code word & retrieve previous one
* @lock : Pointer to queued spinlock structure
* @tail : The new queue tail code word
* Return: The previous queue tail code word
*
* xchg(lock, tail)
*
* p,*,* -> n,*,* ; prev = xchg(lock, node)
*/
static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)
{
u32 old, new, val = atomic_read(&lock->val);
for (;;) {
new = (val & _Q_LOCKED_PENDING_MASK) | tail;
old = atomic_cmpxchg(&lock->val, val, new);
if (old == val)
break;
val = old;
}
return old;
}
#endif /* _Q_PENDING_BITS == 8 */
/**
* set_locked - Set the lock bit and own the lock
* @lock: Pointer to queued spinlock structure
*
* *,*,0 -> *,0,1
*/
static __always_inline void set_locked(struct qspinlock *lock)
{
struct __qspinlock *l = (void *)lock;
WRITE_ONCE(l->locked, _Q_LOCKED_VAL);
}
/*
* Generate the native code for queued_spin_unlock_slowpath(); provide NOPs for
* all the PV callbacks.
*/
static __always_inline void __pv_init_node(struct mcs_spinlock *node) { }
static __always_inline void __pv_wait_node(struct mcs_spinlock *node) { }
static __always_inline void __pv_kick_node(struct qspinlock *lock,
struct mcs_spinlock *node) { }
static __always_inline void __pv_wait_head(struct qspinlock *lock,
struct mcs_spinlock *node) { }
#define pv_enabled() false
#define pv_init_node __pv_init_node
#define pv_wait_node __pv_wait_node
#define pv_kick_node __pv_kick_node
#define pv_wait_head __pv_wait_head
#ifdef CONFIG_PARAVIRT_SPINLOCKS
#define queued_spin_lock_slowpath native_queued_spin_lock_slowpath
#endif
#endif /* _GEN_PV_LOCK_SLOWPATH */
/**
* queued_spin_lock_slowpath - acquire the queued spinlock
* @lock: Pointer to queued spinlock structure
* @val: Current value of the queued spinlock 32-bit word
*
* (queue tail, pending bit, lock value)
*
* fast : slow : unlock
* : :
* uncontended (0,0,0) -:--> (0,0,1) ------------------------------:--> (*,*,0)
* : | ^--------.------. / :
* : v \ \ | :
* pending : (0,1,1) +--> (0,1,0) \ | :
* : | ^--' | | :
* : v | | :
* uncontended : (n,x,y) +--> (n,0,0) --' | :
* queue : | ^--' | :
* : v | :
* contended : (*,x,y) +--> (*,0,0) ---> (*,0,1) -' :
* queue : ^--' :
*/
void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
{
struct mcs_spinlock *prev, *next, *node;
u32 new, old, tail;
int idx;
BUILD_BUG_ON(CONFIG_NR_CPUS >= (1U << _Q_TAIL_CPU_BITS));
if (pv_enabled())
goto queue;
if (virt_spin_lock(lock))
return;
/*
* wait for in-progress pending->locked hand-overs
*
* 0,1,0 -> 0,0,1
*/
if (val == _Q_PENDING_VAL) {
while ((val = atomic_read(&lock->val)) == _Q_PENDING_VAL)
cpu_relax();
}
/*
* trylock || pending
*
* 0,0,0 -> 0,0,1 ; trylock
* 0,0,1 -> 0,1,1 ; pending
*/
for (;;) {
/*
* If we observe any contention; queue.
*/
if (val & ~_Q_LOCKED_MASK)
goto queue;
new = _Q_LOCKED_VAL;
if (val == new)
new |= _Q_PENDING_VAL;
old = atomic_cmpxchg(&lock->val, val, new);
if (old == val)
break;
val = old;
}
/*
* we won the trylock
*/
if (new == _Q_LOCKED_VAL)
return;
/*
* we're pending, wait for the owner to go away.
*
* *,1,1 -> *,1,0
*
* this wait loop must be a load-acquire such that we match the
* store-release that clears the locked bit and create lock
* sequentiality; this is because not all clear_pending_set_locked()
* implementations imply full barriers.
*/
while ((val = smp_load_acquire(&lock->val.counter)) & _Q_LOCKED_MASK)
cpu_relax();
/*
* take ownership and clear the pending bit.
*
* *,1,0 -> *,0,1
*/
clear_pending_set_locked(lock);
return;
/*
* End of pending bit optimistic spinning and beginning of MCS
* queuing.
*/
queue:
node = this_cpu_ptr(&mcs_nodes[0]);
idx = node->count++;
tail = encode_tail(smp_processor_id(), idx);
node += idx;
node->locked = 0;
node->next = NULL;
pv_init_node(node);
/*
* We touched a (possibly) cold cacheline in the per-cpu queue node;
* attempt the trylock once more in the hope someone let go while we
* weren't watching.
*/
if (queued_spin_trylock(lock))
goto release;
/*
* We have already touched the queueing cacheline; don't bother with
* pending stuff.
*
* p,*,* -> n,*,*
*/
old = xchg_tail(lock, tail);
/*
* if there was a previous node; link it and wait until reaching the
* head of the waitqueue.
*/
if (old & _Q_TAIL_MASK) {
prev = decode_tail(old);
WRITE_ONCE(prev->next, node);
pv_wait_node(node);
arch_mcs_spin_lock_contended(&node->locked);
}
/*
* we're at the head of the waitqueue, wait for the owner & pending to
* go away.
*
* *,x,y -> *,0,0
*
* this wait loop must use a load-acquire such that we match the
* store-release that clears the locked bit and create lock
* sequentiality; this is because the set_locked() function below
* does not imply a full barrier.
*
*/
pv_wait_head(lock, node);
while ((val = smp_load_acquire(&lock->val.counter)) & _Q_LOCKED_PENDING_MASK)
cpu_relax();
/*
* claim the lock:
*
* n,0,0 -> 0,0,1 : lock, uncontended
* *,0,0 -> *,0,1 : lock, contended
*
* If the queue head is the only one in the queue (lock value == tail),
* clear the tail code and grab the lock. Otherwise, we only need
* to grab the lock.
*/
for (;;) {
if (val != tail) {
set_locked(lock);
break;
}
old = atomic_cmpxchg(&lock->val, val, _Q_LOCKED_VAL);
if (old == val)
goto release; /* No contention */
val = old;
}
/*
* contended path; wait for next, release.
*/
while (!(next = READ_ONCE(node->next)))
cpu_relax();
arch_mcs_spin_unlock_contended(&next->locked);
pv_kick_node(lock, next);
release:
/*
* release the node
*/
this_cpu_dec(mcs_nodes[0].count);
}
EXPORT_SYMBOL(queued_spin_lock_slowpath);
/*
* Generate the paravirt code for queued_spin_unlock_slowpath().
*/
#if !defined(_GEN_PV_LOCK_SLOWPATH) && defined(CONFIG_PARAVIRT_SPINLOCKS)
#define _GEN_PV_LOCK_SLOWPATH
#undef pv_enabled
#define pv_enabled() true
#undef pv_init_node
#undef pv_wait_node
#undef pv_kick_node
#undef pv_wait_head
#undef queued_spin_lock_slowpath
#define queued_spin_lock_slowpath __pv_queued_spin_lock_slowpath
#include "qspinlock_paravirt.h"
#include "qspinlock.c"
#endif