diff options
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/Makefile | 3 | ||||
| -rw-r--r-- | kernel/locking/lglock.c | 22 | ||||
| -rw-r--r-- | kernel/locking/lockdep.c | 180 | ||||
| -rw-r--r-- | kernel/locking/locktorture.c | 14 | ||||
| -rw-r--r-- | kernel/locking/mcs_spinlock.h | 1 | ||||
| -rw-r--r-- | kernel/locking/qrwlock.c | 30 | ||||
| -rw-r--r-- | kernel/locking/qspinlock.c | 473 | ||||
| -rw-r--r-- | kernel/locking/qspinlock_paravirt.h | 334 | ||||
| -rw-r--r-- | kernel/locking/rtmutex.c | 105 | ||||
| -rw-r--r-- | kernel/locking/rtmutex_common.h | 3 | ||||
| -rw-r--r-- | kernel/locking/rwsem-xadd.c | 44 |
11 files changed, 1066 insertions, 143 deletions
diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile index de7a416cc..7dd5c9918 100644 --- a/kernel/locking/Makefile +++ b/kernel/locking/Makefile @@ -17,6 +17,7 @@ obj-$(CONFIG_SMP) += spinlock.o obj-$(CONFIG_LOCK_SPIN_ON_OWNER) += osq_lock.o obj-$(CONFIG_SMP) += lglock.o obj-$(CONFIG_PROVE_LOCKING) += spinlock.o +obj-$(CONFIG_QUEUED_SPINLOCKS) += qspinlock.o obj-$(CONFIG_RT_MUTEXES) += rtmutex.o obj-$(CONFIG_DEBUG_RT_MUTEXES) += rtmutex-debug.o obj-$(CONFIG_RT_MUTEX_TESTER) += rtmutex-tester.o @@ -25,5 +26,5 @@ obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock_debug.o obj-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o obj-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem-xadd.o obj-$(CONFIG_PERCPU_RWSEM) += percpu-rwsem.o -obj-$(CONFIG_QUEUE_RWLOCK) += qrwlock.o +obj-$(CONFIG_QUEUED_RWLOCKS) += qrwlock.o obj-$(CONFIG_LOCK_TORTURE_TEST) += locktorture.o diff --git a/kernel/locking/lglock.c b/kernel/locking/lglock.c index 86ae2aebf..951cfcd10 100644 --- a/kernel/locking/lglock.c +++ b/kernel/locking/lglock.c @@ -60,6 +60,28 @@ void lg_local_unlock_cpu(struct lglock *lg, int cpu) } EXPORT_SYMBOL(lg_local_unlock_cpu); +void lg_double_lock(struct lglock *lg, int cpu1, int cpu2) +{ + BUG_ON(cpu1 == cpu2); + + /* lock in cpu order, just like lg_global_lock */ + if (cpu2 < cpu1) + swap(cpu1, cpu2); + + preempt_disable(); + lock_acquire_shared(&lg->lock_dep_map, 0, 0, NULL, _RET_IP_); + arch_spin_lock(per_cpu_ptr(lg->lock, cpu1)); + arch_spin_lock(per_cpu_ptr(lg->lock, cpu2)); +} + +void lg_double_unlock(struct lglock *lg, int cpu1, int cpu2) +{ + lock_release(&lg->lock_dep_map, 1, _RET_IP_); + arch_spin_unlock(per_cpu_ptr(lg->lock, cpu1)); + arch_spin_unlock(per_cpu_ptr(lg->lock, cpu2)); + preempt_enable(); +} + void lg_global_lock(struct lglock *lg) { int i; diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index aaeae885d..8acfbf773 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -3157,6 +3157,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, hlock->waittime_stamp = 0; hlock->holdtime_stamp = lockstat_clock(); #endif + hlock->pin_count = 0; if (check && !mark_irqflags(curr, hlock)) return 0; @@ -3260,26 +3261,6 @@ print_unlock_imbalance_bug(struct task_struct *curr, struct lockdep_map *lock, return 0; } -/* - * Common debugging checks for both nested and non-nested unlock: - */ -static int check_unlock(struct task_struct *curr, struct lockdep_map *lock, - unsigned long ip) -{ - if (unlikely(!debug_locks)) - return 0; - /* - * Lockdep should run with IRQs disabled, recursion, head-ache, etc.. - */ - if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) - return 0; - - if (curr->lockdep_depth <= 0) - return print_unlock_imbalance_bug(curr, lock, ip); - - return 1; -} - static int match_held_lock(struct held_lock *hlock, struct lockdep_map *lock) { if (hlock->instance == lock) @@ -3376,31 +3357,35 @@ found_it: } /* - * Remove the lock to the list of currently held locks in a - * potentially non-nested (out of order) manner. This is a - * relatively rare operation, as all the unlock APIs default - * to nested mode (which uses lock_release()): + * Remove the lock to the list of currently held locks - this gets + * called on mutex_unlock()/spin_unlock*() (or on a failed + * mutex_lock_interruptible()). + * + * @nested is an hysterical artifact, needs a tree wide cleanup. */ static int -lock_release_non_nested(struct task_struct *curr, - struct lockdep_map *lock, unsigned long ip) +__lock_release(struct lockdep_map *lock, int nested, unsigned long ip) { + struct task_struct *curr = current; struct held_lock *hlock, *prev_hlock; unsigned int depth; int i; - /* - * Check whether the lock exists in the current stack - * of held locks: - */ + if (unlikely(!debug_locks)) + return 0; + depth = curr->lockdep_depth; /* * So we're all set to release this lock.. wait what lock? We don't * own any locks, you've been drinking again? */ - if (DEBUG_LOCKS_WARN_ON(!depth)) - return 0; + if (DEBUG_LOCKS_WARN_ON(depth <= 0)) + return print_unlock_imbalance_bug(curr, lock, ip); + /* + * Check whether the lock exists in the current stack + * of held locks: + */ prev_hlock = NULL; for (i = depth-1; i >= 0; i--) { hlock = curr->held_locks + i; @@ -3419,6 +3404,8 @@ found_it: if (hlock->instance == lock) lock_release_holdtime(hlock); + WARN(hlock->pin_count, "releasing a pinned lock\n"); + if (hlock->references) { hlock->references--; if (hlock->references) { @@ -3456,91 +3443,66 @@ found_it: */ if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - 1)) return 0; + return 1; } -/* - * Remove the lock to the list of currently held locks - this gets - * called on mutex_unlock()/spin_unlock*() (or on a failed - * mutex_lock_interruptible()). This is done for unlocks that nest - * perfectly. (i.e. the current top of the lock-stack is unlocked) - */ -static int lock_release_nested(struct task_struct *curr, - struct lockdep_map *lock, unsigned long ip) +static int __lock_is_held(struct lockdep_map *lock) { - struct held_lock *hlock; - unsigned int depth; - - /* - * Pop off the top of the lock stack: - */ - depth = curr->lockdep_depth - 1; - hlock = curr->held_locks + depth; - - /* - * Is the unlock non-nested: - */ - if (hlock->instance != lock || hlock->references) - return lock_release_non_nested(curr, lock, ip); - curr->lockdep_depth--; - - /* - * No more locks, but somehow we've got hash left over, who left it? - */ - if (DEBUG_LOCKS_WARN_ON(!depth && (hlock->prev_chain_key != 0))) - return 0; + struct task_struct *curr = current; + int i; - curr->curr_chain_key = hlock->prev_chain_key; + for (i = 0; i < curr->lockdep_depth; i++) { + struct held_lock *hlock = curr->held_locks + i; - lock_release_holdtime(hlock); + if (match_held_lock(hlock, lock)) + return 1; + } -#ifdef CONFIG_DEBUG_LOCKDEP - hlock->prev_chain_key = 0; - hlock->class_idx = 0; - hlock->acquire_ip = 0; - hlock->irq_context = 0; -#endif - return 1; + return 0; } -/* - * Remove the lock to the list of currently held locks - this gets - * called on mutex_unlock()/spin_unlock*() (or on a failed - * mutex_lock_interruptible()). This is done for unlocks that nest - * perfectly. (i.e. the current top of the lock-stack is unlocked) - */ -static void -__lock_release(struct lockdep_map *lock, int nested, unsigned long ip) +static void __lock_pin_lock(struct lockdep_map *lock) { struct task_struct *curr = current; + int i; - if (!check_unlock(curr, lock, ip)) + if (unlikely(!debug_locks)) return; - if (nested) { - if (!lock_release_nested(curr, lock, ip)) - return; - } else { - if (!lock_release_non_nested(curr, lock, ip)) + for (i = 0; i < curr->lockdep_depth; i++) { + struct held_lock *hlock = curr->held_locks + i; + + if (match_held_lock(hlock, lock)) { + hlock->pin_count++; return; + } } - check_chain_key(curr); + WARN(1, "pinning an unheld lock\n"); } -static int __lock_is_held(struct lockdep_map *lock) +static void __lock_unpin_lock(struct lockdep_map *lock) { struct task_struct *curr = current; int i; + if (unlikely(!debug_locks)) + return; + for (i = 0; i < curr->lockdep_depth; i++) { struct held_lock *hlock = curr->held_locks + i; - if (match_held_lock(hlock, lock)) - return 1; + if (match_held_lock(hlock, lock)) { + if (WARN(!hlock->pin_count, "unpinning an unpinned lock\n")) + return; + + hlock->pin_count--; + return; + } } - return 0; + WARN(1, "unpinning an unheld lock\n"); } /* @@ -3639,7 +3601,8 @@ void lock_release(struct lockdep_map *lock, int nested, check_flags(flags); current->lockdep_recursion = 1; trace_lock_release(lock, ip); - __lock_release(lock, nested, ip); + if (__lock_release(lock, nested, ip)) + check_chain_key(current); current->lockdep_recursion = 0; raw_local_irq_restore(flags); } @@ -3665,6 +3628,40 @@ int lock_is_held(struct lockdep_map *lock) } EXPORT_SYMBOL_GPL(lock_is_held); +void lock_pin_lock(struct lockdep_map *lock) +{ + unsigned long flags; + + if (unlikely(current->lockdep_recursion)) + return; + + raw_local_irq_save(flags); + check_flags(flags); + + current->lockdep_recursion = 1; + __lock_pin_lock(lock); + current->lockdep_recursion = 0; + raw_local_irq_restore(flags); +} +EXPORT_SYMBOL_GPL(lock_pin_lock); + +void lock_unpin_lock(struct lockdep_map *lock) +{ + unsigned long flags; + + if (unlikely(current->lockdep_recursion)) + return; + + raw_local_irq_save(flags); + check_flags(flags); + + current->lockdep_recursion = 1; + __lock_unpin_lock(lock); + current->lockdep_recursion = 0; + raw_local_irq_restore(flags); +} +EXPORT_SYMBOL_GPL(lock_unpin_lock); + void lockdep_set_current_reclaim_state(gfp_t gfp_mask) { current->lockdep_reclaim_gfp = gfp_mask; @@ -4067,8 +4064,7 @@ void __init lockdep_info(void) #ifdef CONFIG_DEBUG_LOCKDEP if (lockdep_init_error) { - printk("WARNING: lockdep init error! lock-%s was acquired" - "before lockdep_init\n", lock_init_error); + printk("WARNING: lockdep init error: lock '%s' was acquired before lockdep_init().\n", lock_init_error); printk("Call stack leading to lockdep invocation was:\n"); print_stack_trace(&lockdep_init_trace, 0); } diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c index ec8cce259..32244186f 100644 --- a/kernel/locking/locktorture.c +++ b/kernel/locking/locktorture.c @@ -122,12 +122,12 @@ static int torture_lock_busted_write_lock(void) static void torture_lock_busted_write_delay(struct torture_random_state *trsp) { - const unsigned long longdelay_us = 100; + const unsigned long longdelay_ms = 100; /* We want a long delay occasionally to force massive contention. */ if (!(torture_random(trsp) % - (cxt.nrealwriters_stress * 2000 * longdelay_us))) - mdelay(longdelay_us); + (cxt.nrealwriters_stress * 2000 * longdelay_ms))) + mdelay(longdelay_ms); #ifdef CONFIG_PREEMPT if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000))) preempt_schedule(); /* Allow test to be preempted. */ @@ -160,14 +160,14 @@ static int torture_spin_lock_write_lock(void) __acquires(torture_spinlock) static void torture_spin_lock_write_delay(struct torture_random_state *trsp) { const unsigned long shortdelay_us = 2; - const unsigned long longdelay_us = 100; + const unsigned long longdelay_ms = 100; /* We want a short delay mostly to emulate likely code, and * we want a long delay occasionally to force massive contention. */ if (!(torture_random(trsp) % - (cxt.nrealwriters_stress * 2000 * longdelay_us))) - mdelay(longdelay_us); + (cxt.nrealwriters_stress * 2000 * longdelay_ms))) + mdelay(longdelay_ms); if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 2 * shortdelay_us))) udelay(shortdelay_us); @@ -309,7 +309,7 @@ static int torture_rwlock_read_lock_irq(void) __acquires(torture_rwlock) static void torture_rwlock_read_unlock_irq(void) __releases(torture_rwlock) { - write_unlock_irqrestore(&torture_rwlock, cxt.cur_ops->flags); + read_unlock_irqrestore(&torture_rwlock, cxt.cur_ops->flags); } static struct lock_torture_ops rw_lock_irq_ops = { diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h index 75e114bdf..fd91aaa45 100644 --- a/kernel/locking/mcs_spinlock.h +++ b/kernel/locking/mcs_spinlock.h @@ -17,6 +17,7 @@ struct mcs_spinlock { struct mcs_spinlock *next; int locked; /* 1 if lock acquired */ + int count; /* nesting count, see qspinlock.c */ }; #ifndef arch_mcs_spin_lock_contended diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c index f956ede7f..6c5da4839 100644 --- a/kernel/locking/qrwlock.c +++ b/kernel/locking/qrwlock.c @@ -1,5 +1,5 @@ /* - * Queue read/write lock + * Queued read/write locks * * 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 @@ -22,6 +22,26 @@ #include <linux/hardirq.h> #include <asm/qrwlock.h> +/* + * This internal data structure is used for optimizing access to some of + * the subfields within the atomic_t cnts. + */ +struct __qrwlock { + union { + atomic_t cnts; + struct { +#ifdef __LITTLE_ENDIAN + u8 wmode; /* Writer mode */ + u8 rcnts[3]; /* Reader counts */ +#else + u8 rcnts[3]; /* Reader counts */ + u8 wmode; /* Writer mode */ +#endif + }; + }; + arch_spinlock_t lock; +}; + /** * rspin_until_writer_unlock - inc reader count & spin until writer is gone * @lock : Pointer to queue rwlock structure @@ -107,10 +127,10 @@ void queue_write_lock_slowpath(struct qrwlock *lock) * or wait for a previous writer to go away. */ for (;;) { - cnts = atomic_read(&lock->cnts); - if (!(cnts & _QW_WMASK) && - (atomic_cmpxchg(&lock->cnts, cnts, - cnts | _QW_WAITING) == cnts)) + struct __qrwlock *l = (struct __qrwlock *)lock; + + if (!READ_ONCE(l->wmode) && + (cmpxchg(&l->wmode, 0, _QW_WAITING) == 0)) break; cpu_relax_lowlatency(); diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c new file mode 100644 index 000000000..38c49202d --- /dev/null +++ b/kernel/locking/qspinlock.c @@ -0,0 +1,473 @@ +/* + * 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 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_queued_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(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 diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h new file mode 100644 index 000000000..df19ae4de --- /dev/null +++ b/kernel/locking/qspinlock_paravirt.h @@ -0,0 +1,334 @@ +#ifndef _GEN_PV_LOCK_SLOWPATH +#error "do not include this file" +#endif + +#include <linux/hash.h> +#include <linux/bootmem.h> +#include <linux/debug_locks.h> + +/* + * Implement paravirt qspinlocks; the general idea is to halt the vcpus instead + * of spinning them. + * + * This relies on the architecture to provide two paravirt hypercalls: + * + * pv_wait(u8 *ptr, u8 val) -- suspends the vcpu if *ptr == val + * pv_kick(cpu) -- wakes a suspended vcpu + * + * Using these we implement __pv_queued_spin_lock_slowpath() and + * __pv_queued_spin_unlock() to replace native_queued_spin_lock_slowpath() and + * native_queued_spin_unlock(). + */ + +#define _Q_SLOW_VAL (3U << _Q_LOCKED_OFFSET) + +enum vcpu_state { + vcpu_running = 0, + vcpu_halted, +}; + +struct pv_node { + struct mcs_spinlock mcs; + struct mcs_spinlock __res[3]; + + int cpu; + u8 state; +}; + +/* + * Lock and MCS node addresses hash table for fast lookup + * + * Hashing is done on a per-cacheline basis to minimize the need to access + * more than one cacheline. + * + * Dynamically allocate a hash table big enough to hold at least 4X the + * number of possible cpus in the system. Allocation is done on page + * granularity. So the minimum number of hash buckets should be at least + * 256 (64-bit) or 512 (32-bit) to fully utilize a 4k page. + * + * Since we should not be holding locks from NMI context (very rare indeed) the + * max load factor is 0.75, which is around the point where open addressing + * breaks down. + * + */ +struct pv_hash_entry { + struct qspinlock *lock; + struct pv_node *node; +}; + +#define PV_HE_PER_LINE (SMP_CACHE_BYTES / sizeof(struct pv_hash_entry)) +#define PV_HE_MIN (PAGE_SIZE / sizeof(struct pv_hash_entry)) + +static struct pv_hash_entry *pv_lock_hash; +static unsigned int pv_lock_hash_bits __read_mostly; + +/* + * Allocate memory for the PV qspinlock hash buckets + * + * This function should be called from the paravirt spinlock initialization + * routine. + */ +void __init __pv_init_lock_hash(void) +{ + int pv_hash_size = ALIGN(4 * num_possible_cpus(), PV_HE_PER_LINE); + + if (pv_hash_size < PV_HE_MIN) + pv_hash_size = PV_HE_MIN; + + /* + * Allocate space from bootmem which should be page-size aligned + * and hence cacheline aligned. + */ + pv_lock_hash = alloc_large_system_hash("PV qspinlock", + sizeof(struct pv_hash_entry), + pv_hash_size, 0, HASH_EARLY, + &pv_lock_hash_bits, NULL, + pv_hash_size, pv_hash_size); +} + +#define for_each_hash_entry(he, offset, hash) \ + for (hash &= ~(PV_HE_PER_LINE - 1), he = &pv_lock_hash[hash], offset = 0; \ + offset < (1 << pv_lock_hash_bits); \ + offset++, he = &pv_lock_hash[(hash + offset) & ((1 << pv_lock_hash_bits) - 1)]) + +static struct qspinlock **pv_hash(struct qspinlock *lock, struct pv_node *node) +{ + unsigned long offset, hash = hash_ptr(lock, pv_lock_hash_bits); + struct pv_hash_entry *he; + + for_each_hash_entry(he, offset, hash) { + if (!cmpxchg(&he->lock, NULL, lock)) { + WRITE_ONCE(he->node, node); + return &he->lock; + } + } + /* + * Hard assume there is a free entry for us. + * + * This is guaranteed by ensuring every blocked lock only ever consumes + * a single entry, and since we only have 4 nesting levels per CPU + * and allocated 4*nr_possible_cpus(), this must be so. + * + * The single entry is guaranteed by having the lock owner unhash + * before it releases. + */ + BUG(); +} + +static struct pv_node *pv_unhash(struct qspinlock *lock) +{ + unsigned long offset, hash = hash_ptr(lock, pv_lock_hash_bits); + struct pv_hash_entry *he; + struct pv_node *node; + + for_each_hash_entry(he, offset, hash) { + if (READ_ONCE(he->lock) == lock) { + node = READ_ONCE(he->node); + WRITE_ONCE(he->lock, NULL); + return node; + } + } + /* + * Hard assume we'll find an entry. + * + * This guarantees a limited lookup time and is itself guaranteed by + * having the lock owner do the unhash -- IFF the unlock sees the + * SLOW flag, there MUST be a hash entry. + */ + BUG(); +} + +/* + * Initialize the PV part of the mcs_spinlock node. + */ +static void pv_init_node(struct mcs_spinlock *node) +{ + struct pv_node *pn = (struct pv_node *)node; + + BUILD_BUG_ON(sizeof(struct pv_node) > 5*sizeof(struct mcs_spinlock)); + + pn->cpu = smp_processor_id(); + pn->state = vcpu_running; +} + +/* + * Wait for node->locked to become true, halt the vcpu after a short spin. + * pv_kick_node() is used to wake the vcpu again. + */ +static void pv_wait_node(struct mcs_spinlock *node) +{ + struct pv_node *pn = (struct pv_node *)node; + int loop; + + for (;;) { + for (loop = SPIN_THRESHOLD; loop; loop--) { + if (READ_ONCE(node->locked)) + return; + cpu_relax(); + } + + /* + * Order pn->state vs pn->locked thusly: + * + * [S] pn->state = vcpu_halted [S] next->locked = 1 + * MB MB + * [L] pn->locked [RmW] pn->state = vcpu_running + * + * Matches the xchg() from pv_kick_node(). + */ + smp_store_mb(pn->state, vcpu_halted); + + if (!READ_ONCE(node->locked)) + pv_wait(&pn->state, vcpu_halted); + + /* + * Reset the vCPU state to avoid unncessary CPU kicking + */ + WRITE_ONCE(pn->state, vcpu_running); + + /* + * If the locked flag is still not set after wakeup, it is a + * spurious wakeup and the vCPU should wait again. However, + * there is a pretty high overhead for CPU halting and kicking. + * So it is better to spin for a while in the hope that the + * MCS lock will be released soon. + */ + } + /* + * By now our node->locked should be 1 and our caller will not actually + * spin-wait for it. We do however rely on our caller to do a + * load-acquire for us. + */ +} + +/* + * Called after setting next->locked = 1, used to wake those stuck in + * pv_wait_node(). + */ +static void pv_kick_node(struct mcs_spinlock *node) +{ + struct pv_node *pn = (struct pv_node *)node; + + /* + * Note that because node->locked is already set, this actual + * mcs_spinlock entry could be re-used already. + * + * This should be fine however, kicking people for no reason is + * harmless. + * + * See the comment in pv_wait_node(). + */ + if (xchg(&pn->state, vcpu_running) == vcpu_halted) + pv_kick(pn->cpu); +} + +/* + * Wait for l->locked to become clear; halt the vcpu after a short spin. + * __pv_queued_spin_unlock() will wake us. + */ +static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node) +{ + struct pv_node *pn = (struct pv_node *)node; + struct __qspinlock *l = (void *)lock; + struct qspinlock **lp = NULL; + int loop; + + for (;;) { + for (loop = SPIN_THRESHOLD; loop; loop--) { + if (!READ_ONCE(l->locked)) + return; + cpu_relax(); + } + + WRITE_ONCE(pn->state, vcpu_halted); + if (!lp) { /* ONCE */ + lp = pv_hash(lock, pn); + /* + * lp must be set before setting _Q_SLOW_VAL + * + * [S] lp = lock [RmW] l = l->locked = 0 + * MB MB + * [S] l->locked = _Q_SLOW_VAL [L] lp + * + * Matches the cmpxchg() in __pv_queued_spin_unlock(). + */ + if (!cmpxchg(&l->locked, _Q_LOCKED_VAL, _Q_SLOW_VAL)) { + /* + * The lock is free and _Q_SLOW_VAL has never + * been set. Therefore we need to unhash before + * getting the lock. + */ + WRITE_ONCE(*lp, NULL); + return; + } + } + pv_wait(&l->locked, _Q_SLOW_VAL); + + /* + * The unlocker should have freed the lock before kicking the + * CPU. So if the lock is still not free, it is a spurious + * wakeup and so the vCPU should wait again after spinning for + * a while. + */ + } + + /* + * Lock is unlocked now; the caller will acquire it without waiting. + * As with pv_wait_node() we rely on the caller to do a load-acquire + * for us. + */ +} + +/* + * PV version of the unlock function to be used in stead of + * queued_spin_unlock(). + */ +__visible void __pv_queued_spin_unlock(struct qspinlock *lock) +{ + struct __qspinlock *l = (void *)lock; + struct pv_node *node; + u8 lockval = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0); + + /* + * We must not unlock if SLOW, because in that case we must first + * unhash. Otherwise it would be possible to have multiple @lock + * entries, which would be BAD. + */ + if (likely(lockval == _Q_LOCKED_VAL)) + return; + + if (unlikely(lockval != _Q_SLOW_VAL)) { + if (debug_locks_silent) + return; + WARN(1, "pvqspinlock: lock %p has corrupted value 0x%x!\n", lock, atomic_read(&lock->val)); + return; + } + + /* + * Since the above failed to release, this must be the SLOW path. + * Therefore start by looking up the blocked node and unhashing it. + */ + node = pv_unhash(lock); + + /* + * Now that we have a reference to the (likely) blocked pv_node, + * release the lock. + */ + smp_store_release(&l->locked, 0); + + /* + * At this point the memory pointed at by lock can be freed/reused, + * however we can still use the pv_node to kick the CPU. + */ + if (READ_ONCE(node->state) == vcpu_halted) + pv_kick(node->cpu); +} +/* + * Include the architecture specific callee-save thunk of the + * __pv_queued_spin_unlock(). This thunk is put together with + * __pv_queued_spin_unlock() near the top of the file to make sure + * that the callee-save thunk and the real unlock function are close + * to each other sharing consecutive instruction cachelines. + */ +#include <asm/qspinlock_paravirt.h> + diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index b025295f4..5674b0734 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -70,10 +70,10 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock) } /* - * We can speed up the acquire/release, if the architecture - * supports cmpxchg and if there's no debugging state to be set up + * We can speed up the acquire/release, if there's no debugging state to be + * set up. */ -#if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES) +#ifndef CONFIG_DEBUG_RT_MUTEXES # define rt_mutex_cmpxchg(l,c,n) (cmpxchg(&l->owner, c, n) == c) static inline void mark_rt_mutex_waiters(struct rt_mutex *lock) { @@ -300,7 +300,7 @@ static void __rt_mutex_adjust_prio(struct task_struct *task) * of task. We do not use the spin_xx_mutex() variants here as we are * outside of the debug path.) */ -static void rt_mutex_adjust_prio(struct task_struct *task) +void rt_mutex_adjust_prio(struct task_struct *task) { unsigned long flags; @@ -624,7 +624,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task, */ prerequeue_top_waiter = rt_mutex_top_waiter(lock); - /* [7] Requeue the waiter in the lock waiter list. */ + /* [7] Requeue the waiter in the lock waiter tree. */ rt_mutex_dequeue(lock, waiter); waiter->prio = task->prio; rt_mutex_enqueue(lock, waiter); @@ -662,7 +662,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task, /* * The waiter became the new top (highest priority) * waiter on the lock. Replace the previous top waiter - * in the owner tasks pi waiters list with this waiter + * in the owner tasks pi waiters tree with this waiter * and adjust the priority of the owner. */ rt_mutex_dequeue_pi(task, prerequeue_top_waiter); @@ -673,7 +673,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task, /* * The waiter was the top waiter on the lock, but is * no longer the top prority waiter. Replace waiter in - * the owner tasks pi waiters list with the new top + * the owner tasks pi waiters tree with the new top * (highest priority) waiter and adjust the priority * of the owner. * The new top waiter is stored in @waiter so that @@ -747,7 +747,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task, * * @lock: The lock to be acquired. * @task: The task which wants to acquire the lock - * @waiter: The waiter that is queued to the lock's wait list if the + * @waiter: The waiter that is queued to the lock's wait tree if the * callsite called task_blocked_on_lock(), otherwise NULL */ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task, @@ -782,7 +782,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task, /* * If @waiter != NULL, @task has already enqueued the waiter - * into @lock waiter list. If @waiter == NULL then this is a + * into @lock waiter tree. If @waiter == NULL then this is a * trylock attempt. */ if (waiter) { @@ -795,7 +795,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task, /* * We can acquire the lock. Remove the waiter from the - * lock waiters list. + * lock waiters tree. */ rt_mutex_dequeue(lock, waiter); @@ -827,7 +827,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task, * No waiters. Take the lock without the * pi_lock dance.@task->pi_blocked_on is NULL * and we have no waiters to enqueue in @task - * pi waiters list. + * pi waiters tree. */ goto takeit; } @@ -844,7 +844,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task, /* * Finish the lock acquisition. @task is the new owner. If * other waiters exist we have to insert the highest priority - * waiter into @task->pi_waiters list. + * waiter into @task->pi_waiters tree. */ if (rt_mutex_has_waiters(lock)) rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock)); @@ -955,14 +955,13 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock, } /* - * Wake up the next waiter on the lock. - * - * Remove the top waiter from the current tasks pi waiter list and - * wake it up. + * Remove the top waiter from the current tasks pi waiter tree and + * queue it up. * * Called with lock->wait_lock held. */ -static void wakeup_next_waiter(struct rt_mutex *lock) +static void mark_wakeup_next_waiter(struct wake_q_head *wake_q, + struct rt_mutex *lock) { struct rt_mutex_waiter *waiter; unsigned long flags; @@ -991,12 +990,7 @@ static void wakeup_next_waiter(struct rt_mutex *lock) raw_spin_unlock_irqrestore(¤t->pi_lock, flags); - /* - * It's safe to dereference waiter as it cannot go away as - * long as we hold lock->wait_lock. The waiter task needs to - * acquire it in order to dequeue the waiter. - */ - wake_up_process(waiter->task); + wake_q_add(wake_q, waiter->task); } /* @@ -1182,11 +1176,8 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state, set_current_state(state); /* Setup the timer, when timeout != NULL */ - if (unlikely(timeout)) { + if (unlikely(timeout)) hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS); - if (!hrtimer_active(&timeout->timer)) - timeout->task = NULL; - } ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk); @@ -1253,10 +1244,11 @@ static inline int rt_mutex_slowtrylock(struct rt_mutex *lock) } /* - * Slow path to release a rt-mutex: + * Slow path to release a rt-mutex. + * Return whether the current task needs to undo a potential priority boosting. */ -static void __sched -rt_mutex_slowunlock(struct rt_mutex *lock) +static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock, + struct wake_q_head *wake_q) { raw_spin_lock(&lock->wait_lock); @@ -1298,7 +1290,7 @@ rt_mutex_slowunlock(struct rt_mutex *lock) while (!rt_mutex_has_waiters(lock)) { /* Drops lock->wait_lock ! */ if (unlock_rt_mutex_safe(lock) == true) - return; + return false; /* Relock the rtmutex and try again */ raw_spin_lock(&lock->wait_lock); } @@ -1306,13 +1298,15 @@ rt_mutex_slowunlock(struct rt_mutex *lock) /* * The wakeup next waiter path does not suffer from the above * race. See the comments there. + * + * Queue the next waiter for wakeup once we release the wait_lock. */ - wakeup_next_waiter(lock); + mark_wakeup_next_waiter(wake_q, lock); raw_spin_unlock(&lock->wait_lock); - /* Undo pi boosting if necessary: */ - rt_mutex_adjust_prio(current); + /* check PI boosting */ + return true; } /* @@ -1363,12 +1357,23 @@ rt_mutex_fasttrylock(struct rt_mutex *lock, static inline void rt_mutex_fastunlock(struct rt_mutex *lock, - void (*slowfn)(struct rt_mutex *lock)) + bool (*slowfn)(struct rt_mutex *lock, + struct wake_q_head *wqh)) { - if (likely(rt_mutex_cmpxchg(lock, current, NULL))) + WAKE_Q(wake_q); + + if (likely(rt_mutex_cmpxchg(lock, current, NULL))) { rt_mutex_deadlock_account_unlock(current); - else - slowfn(lock); + + } else { + bool deboost = slowfn(lock, &wake_q); + + wake_up_q(&wake_q); + + /* Undo pi boosting if necessary: */ + if (deboost) + rt_mutex_adjust_prio(current); + } } /** @@ -1443,10 +1448,17 @@ EXPORT_SYMBOL_GPL(rt_mutex_timed_lock); * * @lock: the rt_mutex to be locked * + * This function can only be called in thread context. It's safe to + * call it from atomic regions, but not from hard interrupt or soft + * interrupt context. + * * Returns 1 on success and 0 on contention */ int __sched rt_mutex_trylock(struct rt_mutex *lock) { + if (WARN_ON(in_irq() || in_nmi() || in_serving_softirq())) + return 0; + return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock); } EXPORT_SYMBOL_GPL(rt_mutex_trylock); @@ -1463,6 +1475,23 @@ void __sched rt_mutex_unlock(struct rt_mutex *lock) EXPORT_SYMBOL_GPL(rt_mutex_unlock); /** + * rt_mutex_futex_unlock - Futex variant of rt_mutex_unlock + * @lock: the rt_mutex to be unlocked + * + * Returns: true/false indicating whether priority adjustment is + * required or not. + */ +bool __sched rt_mutex_futex_unlock(struct rt_mutex *lock, + struct wake_q_head *wqh) +{ + if (likely(rt_mutex_cmpxchg(lock, current, NULL))) { + rt_mutex_deadlock_account_unlock(current); + return false; + } + return rt_mutex_slowunlock(lock, wqh); +} + +/** * rt_mutex_destroy - mark a mutex unusable * @lock: the mutex to be destroyed * diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h index 855212501..7844f8f0e 100644 --- a/kernel/locking/rtmutex_common.h +++ b/kernel/locking/rtmutex_common.h @@ -131,6 +131,9 @@ extern int rt_mutex_finish_proxy_lock(struct rt_mutex *lock, struct hrtimer_sleeper *to, struct rt_mutex_waiter *waiter); extern int rt_mutex_timed_futex_lock(struct rt_mutex *l, struct hrtimer_sleeper *to); +extern bool rt_mutex_futex_unlock(struct rt_mutex *lock, + struct wake_q_head *wqh); +extern void rt_mutex_adjust_prio(struct task_struct *task); #ifdef CONFIG_DEBUG_RT_MUTEXES # include "rtmutex-debug.h" diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 3417d0172..0f189714e 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -409,11 +409,24 @@ done: return taken; } +/* + * Return true if the rwsem has active spinner + */ +static inline bool rwsem_has_spinner(struct rw_semaphore *sem) +{ + return osq_is_locked(&sem->osq); +} + #else static bool rwsem_optimistic_spin(struct rw_semaphore *sem) { return false; } + +static inline bool rwsem_has_spinner(struct rw_semaphore *sem) +{ + return false; +} #endif /* @@ -496,7 +509,38 @@ struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem) { unsigned long flags; + /* + * If a spinner is present, it is not necessary to do the wakeup. + * Try to do wakeup only if the trylock succeeds to minimize + * spinlock contention which may introduce too much delay in the + * unlock operation. + * + * spinning writer up_write/up_read caller + * --------------- ----------------------- + * [S] osq_unlock() [L] osq + * MB RMB + * [RmW] rwsem_try_write_lock() [RmW] spin_trylock(wait_lock) + * + * Here, it is important to make sure that there won't be a missed + * wakeup while the rwsem is free and the only spinning writer goes + * to sleep without taking the rwsem. Even when the spinning writer + * is just going to break out of the waiting loop, it will still do + * a trylock in rwsem_down_write_failed() before sleeping. IOW, if + * rwsem_has_spinner() is true, it will guarantee at least one + * trylock attempt on the rwsem later on. + */ + if (rwsem_has_spinner(sem)) { + /* + * The smp_rmb() here is to make sure that the spinner + * state is consulted before reading the wait_lock. + */ + smp_rmb(); + if (!raw_spin_trylock_irqsave(&sem->wait_lock, flags)) + return sem; + goto locked; + } raw_spin_lock_irqsave(&sem->wait_lock, flags); +locked: /* do nothing if list empty */ if (!list_empty(&sem->wait_list)) |