diff options
| -rw-r--r-- | include/linux/mutex.h | 3 | ||||
| -rw-r--r-- | include/linux/sched.h | 1 | ||||
| -rw-r--r-- | kernel/lockdep.c | 29 | ||||
| -rw-r--r-- | kernel/mutex.c | 151 | ||||
| -rw-r--r-- | kernel/rtmutex-tester.c | 5 | ||||
| -rw-r--r-- | kernel/sched/core.c | 45 | ||||
| -rw-r--r-- | kernel/sched/features.h | 7 |
7 files changed, 168 insertions, 73 deletions
diff --git a/include/linux/mutex.h b/include/linux/mutex.h index 9121595..433da8a 100644 --- a/include/linux/mutex.h +++ b/include/linux/mutex.h @@ -53,6 +53,9 @@ struct mutex { #if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP) struct task_struct *owner; #endif +#ifdef CONFIG_MUTEX_SPIN_ON_OWNER + void *spin_mlock; /* Spinner MCS lock */ +#endif #ifdef CONFIG_DEBUG_MUTEXES const char *name; void *magic; diff --git a/include/linux/sched.h b/include/linux/sched.h index e692a02..2d02c76 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -321,7 +321,6 @@ extern signed long schedule_timeout_killable(signed long timeout); extern signed long schedule_timeout_uninterruptible(signed long timeout); asmlinkage void schedule(void); extern void schedule_preempt_disabled(void); -extern int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner); struct nsproxy; struct user_namespace; diff --git a/kernel/lockdep.c b/kernel/lockdep.c index 8a0efac..6a3bccb 100644 --- a/kernel/lockdep.c +++ b/kernel/lockdep.c @@ -380,6 +380,13 @@ static int verbose(struct lock_class *class) unsigned long nr_stack_trace_entries; static unsigned long stack_trace[MAX_STACK_TRACE_ENTRIES]; +static void print_lockdep_off(const char *bug_msg) +{ + printk(KERN_DEBUG "%s\n", bug_msg); + printk(KERN_DEBUG "turning off the locking correctness validator.\n"); + printk(KERN_DEBUG "Please attach the output of /proc/lock_stat to the bug report\n"); +} + static int save_trace(struct stack_trace *trace) { trace->nr_entries = 0; @@ -409,8 +416,7 @@ static int save_trace(struct stack_trace *trace) if (!debug_locks_off_graph_unlock()) return 0; - printk("BUG: MAX_STACK_TRACE_ENTRIES too low!\n"); - printk("turning off the locking correctness validator.\n"); + print_lockdep_off("BUG: MAX_STACK_TRACE_ENTRIES too low!"); dump_stack(); return 0; @@ -763,8 +769,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force) } raw_local_irq_restore(flags); - printk("BUG: MAX_LOCKDEP_KEYS too low!\n"); - printk("turning off the locking correctness validator.\n"); + print_lockdep_off("BUG: MAX_LOCKDEP_KEYS too low!"); dump_stack(); return NULL; } @@ -834,8 +839,7 @@ static struct lock_list *alloc_list_entry(void) if (!debug_locks_off_graph_unlock()) return NULL; - printk("BUG: MAX_LOCKDEP_ENTRIES too low!\n"); - printk("turning off the locking correctness validator.\n"); + print_lockdep_off("BUG: MAX_LOCKDEP_ENTRIES too low!"); dump_stack(); return NULL; } @@ -2000,7 +2004,7 @@ static inline int lookup_chain_cache(struct task_struct *curr, struct lock_class *class = hlock_class(hlock); struct list_head *hash_head = chainhashentry(chain_key); struct lock_chain *chain; - struct held_lock *hlock_curr, *hlock_next; + struct held_lock *hlock_curr; int i, j; /* @@ -2048,8 +2052,7 @@ cache_hit: if (!debug_locks_off_graph_unlock()) return 0; - printk("BUG: MAX_LOCKDEP_CHAINS too low!\n"); - printk("turning off the locking correctness validator.\n"); + print_lockdep_off("BUG: MAX_LOCKDEP_CHAINS too low!"); dump_stack(); return 0; } @@ -2057,12 +2060,10 @@ cache_hit: chain->chain_key = chain_key; chain->irq_context = hlock->irq_context; /* Find the first held_lock of current chain */ - hlock_next = hlock; for (i = curr->lockdep_depth - 1; i >= 0; i--) { hlock_curr = curr->held_locks + i; - if (hlock_curr->irq_context != hlock_next->irq_context) + if (hlock_curr->irq_context != hlock->irq_context) break; - hlock_next = hlock; } i++; chain->depth = curr->lockdep_depth + 1 - i; @@ -3190,9 +3191,9 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, #endif if (unlikely(curr->lockdep_depth >= MAX_LOCK_DEPTH)) { debug_locks_off(); - printk("BUG: MAX_LOCK_DEPTH too low, depth: %i max: %lu!\n", + print_lockdep_off("BUG: MAX_LOCK_DEPTH too low!"); + printk(KERN_DEBUG "depth: %i max: %lu!\n", curr->lockdep_depth, MAX_LOCK_DEPTH); - printk("turning off the locking correctness validator.\n"); lockdep_print_held_locks(current); debug_show_all_locks(); diff --git a/kernel/mutex.c b/kernel/mutex.c index 52f2301..ad53a66 100644 --- a/kernel/mutex.c +++ b/kernel/mutex.c @@ -37,6 +37,12 @@ # include <asm/mutex.h> #endif +/* + * A negative mutex count indicates that waiters are sleeping waiting for the + * mutex. + */ +#define MUTEX_SHOW_NO_WAITER(mutex) (atomic_read(&(mutex)->count) >= 0) + void __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) { @@ -44,6 +50,9 @@ __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) spin_lock_init(&lock->wait_lock); INIT_LIST_HEAD(&lock->wait_list); mutex_clear_owner(lock); +#ifdef CONFIG_MUTEX_SPIN_ON_OWNER + lock->spin_mlock = NULL; +#endif debug_mutex_init(lock, name, key); } @@ -95,6 +104,124 @@ void __sched mutex_lock(struct mutex *lock) EXPORT_SYMBOL(mutex_lock); #endif +#ifdef CONFIG_MUTEX_SPIN_ON_OWNER +/* + * In order to avoid a stampede of mutex spinners from acquiring the mutex + * more or less simultaneously, the spinners need to acquire a MCS lock + * first before spinning on the owner field. + * + * We don't inline mspin_lock() so that perf can correctly account for the + * time spent in this lock function. + */ +struct mspin_node { + struct mspin_node *next ; + int locked; /* 1 if lock acquired */ +}; +#define MLOCK(mutex) ((struct mspin_node **)&((mutex)->spin_mlock)) + +static noinline +void mspin_lock(struct mspin_node **lock, struct mspin_node *node) +{ + struct mspin_node *prev; + + /* Init node */ + node->locked = 0; + node->next = NULL; + + prev = xchg(lock, node); + if (likely(prev == NULL)) { + /* Lock acquired */ + node->locked = 1; + return; + } + ACCESS_ONCE(prev->next) = node; + smp_wmb(); + /* Wait until the lock holder passes the lock down */ + while (!ACCESS_ONCE(node->locked)) + arch_mutex_cpu_relax(); +} + +static void mspin_unlock(struct mspin_node **lock, struct mspin_node *node) +{ + struct mspin_node *next = ACCESS_ONCE(node->next); + + if (likely(!next)) { + /* + * Release the lock by setting it to NULL + */ + if (cmpxchg(lock, node, NULL) == node) + return; + /* Wait until the next pointer is set */ + while (!(next = ACCESS_ONCE(node->next))) + arch_mutex_cpu_relax(); + } + ACCESS_ONCE(next->locked) = 1; + smp_wmb(); +} + +/* + * Mutex spinning code migrated from kernel/sched/core.c + */ + +static inline bool owner_running(struct mutex *lock, struct task_struct *owner) +{ + if (lock->owner != owner) + return false; + + /* + * Ensure we emit the owner->on_cpu, dereference _after_ checking + * lock->owner still matches owner, if that fails, owner might + * point to free()d memory, if it still matches, the rcu_read_lock() + * ensures the memory stays valid. + */ + barrier(); + + return owner->on_cpu; +} + +/* + * Look out! "owner" is an entirely speculative pointer + * access and not reliable. + */ +static noinline +int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) +{ + rcu_read_lock(); + while (owner_running(lock, owner)) { + if (need_resched()) + break; + + arch_mutex_cpu_relax(); + } + rcu_read_unlock(); + + /* + * We break out the loop above on need_resched() and when the + * owner changed, which is a sign for heavy contention. Return + * success only when lock->owner is NULL. + */ + return lock->owner == NULL; +} + +/* + * Initial check for entering the mutex spinning loop + */ +static inline int mutex_can_spin_on_owner(struct mutex *lock) +{ + int retval = 1; + + rcu_read_lock(); + if (lock->owner) + retval = lock->owner->on_cpu; + rcu_read_unlock(); + /* + * if lock->owner is not set, the mutex owner may have just acquired + * it and not set the owner yet or the mutex has been released. + */ + return retval; +} +#endif + static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count); /** @@ -158,25 +285,39 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, * * We can't do this for DEBUG_MUTEXES because that relies on wait_lock * to serialize everything. + * + * The mutex spinners are queued up using MCS lock so that only one + * spinner can compete for the mutex. However, if mutex spinning isn't + * going to happen, there is no point in going through the lock/unlock + * overhead. */ + if (!mutex_can_spin_on_owner(lock)) + goto slowpath; for (;;) { struct task_struct *owner; + struct mspin_node node; /* * If there's an owner, wait for it to either * release the lock or go to sleep. */ + mspin_lock(MLOCK(lock), &node); owner = ACCESS_ONCE(lock->owner); - if (owner && !mutex_spin_on_owner(lock, owner)) + if (owner && !mutex_spin_on_owner(lock, owner)) { + mspin_unlock(MLOCK(lock), &node); break; + } - if (atomic_cmpxchg(&lock->count, 1, 0) == 1) { + if ((atomic_read(&lock->count) == 1) && + (atomic_cmpxchg(&lock->count, 1, 0) == 1)) { lock_acquired(&lock->dep_map, ip); mutex_set_owner(lock); + mspin_unlock(MLOCK(lock), &node); preempt_enable(); return 0; } + mspin_unlock(MLOCK(lock), &node); /* * When there's no owner, we might have preempted between the @@ -195,6 +336,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, */ arch_mutex_cpu_relax(); } +slowpath: #endif spin_lock_mutex(&lock->wait_lock, flags); @@ -205,7 +347,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, list_add_tail(&waiter.list, &lock->wait_list); waiter.task = task; - if (atomic_xchg(&lock->count, -1) == 1) + if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, -1) == 1)) goto done; lock_contended(&lock->dep_map, ip); @@ -220,7 +362,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, * that when we release the lock, we properly wake up the * other waiters: */ - if (atomic_xchg(&lock->count, -1) == 1) + if (MUTEX_SHOW_NO_WAITER(lock) && + (atomic_xchg(&lock->count, -1) == 1)) break; /* diff --git a/kernel/rtmutex-tester.c b/kernel/rtmutex-tester.c index 7890b10..1d96dd0 100644 --- a/kernel/rtmutex-tester.c +++ b/kernel/rtmutex-tester.c @@ -14,6 +14,7 @@ #include <linux/spinlock.h> #include <linux/timer.h> #include <linux/freezer.h> +#include <linux/stat.h> #include "rtmutex.h" @@ -366,8 +367,8 @@ static ssize_t sysfs_test_status(struct device *dev, struct device_attribute *at return curr - buf; } -static DEVICE_ATTR(status, 0600, sysfs_test_status, NULL); -static DEVICE_ATTR(command, 0600, NULL, sysfs_test_command); +static DEVICE_ATTR(status, S_IRUSR, sysfs_test_status, NULL); +static DEVICE_ATTR(command, S_IWUSR, NULL, sysfs_test_command); static struct bus_type rttest_subsys = { .name = "rttest", diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 67d0465..4205354 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2999,51 +2999,6 @@ void __sched schedule_preempt_disabled(void) preempt_disable(); } -#ifdef CONFIG_MUTEX_SPIN_ON_OWNER - -static inline bool owner_running(struct mutex *lock, struct task_struct *owner) -{ - if (lock->owner != owner) - return false; - - /* - * Ensure we emit the owner->on_cpu, dereference _after_ checking - * lock->owner still matches owner, if that fails, owner might - * point to free()d memory, if it still matches, the rcu_read_lock() - * ensures the memory stays valid. - */ - barrier(); - - return owner->on_cpu; -} - -/* - * Look out! "owner" is an entirely speculative pointer - * access and not reliable. - */ -int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) -{ - if (!sched_feat(OWNER_SPIN)) - return 0; - - rcu_read_lock(); - while (owner_running(lock, owner)) { - if (need_resched()) - break; - - arch_mutex_cpu_relax(); - } - rcu_read_unlock(); - - /* - * We break out the loop above on need_resched() and when the - * owner changed, which is a sign for heavy contention. Return - * success only when lock->owner is NULL. - */ - return lock->owner == NULL; -} -#endif - #ifdef CONFIG_PREEMPT /* * this is the entry point to schedule() from in-kernel preemption diff --git a/kernel/sched/features.h b/kernel/sched/features.h index 1ad1d2b..99399f8 100644 --- a/kernel/sched/features.h +++ b/kernel/sched/features.h @@ -46,13 +46,6 @@ SCHED_FEAT(DOUBLE_TICK, false) SCHED_FEAT(LB_BIAS, true) /* - * Spin-wait on mutex acquisition when the mutex owner is running on - * another cpu -- assumes that when the owner is running, it will soon - * release the lock. Decreases scheduling overhead. - */ -SCHED_FEAT(OWNER_SPIN, true) - -/* * Decrement CPU power based on time not spent running tasks */ SCHED_FEAT(NONTASK_POWER, true) |
