diff options
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/lockdep.c | 116 | ||||
| -rw-r--r-- | kernel/locking/lockdep_internals.h | 27 | ||||
| -rw-r--r-- | kernel/locking/lockdep_proc.c | 2 | ||||
| -rw-r--r-- | kernel/locking/qspinlock.c | 143 | ||||
| -rw-r--r-- | kernel/locking/qspinlock_paravirt.h | 4 | ||||
| -rw-r--r-- | kernel/locking/qspinlock_stat.h | 6 | ||||
| -rw-r--r-- | kernel/locking/rtmutex.c | 4 | ||||
| -rw-r--r-- | kernel/locking/rwsem-xadd.c | 15 | ||||
| -rw-r--r-- | kernel/locking/rwsem.c | 7 | ||||
| -rw-r--r-- | kernel/locking/rwsem.h | 95 | ||||
| -rw-r--r-- | kernel/locking/test-ww_mutex.c | 10 |
11 files changed, 258 insertions, 171 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index dd13f865ad40..1efada2dd9dd 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -138,7 +138,7 @@ static struct lock_list list_entries[MAX_LOCKDEP_ENTRIES]; * get freed - this significantly simplifies the debugging code. */ unsigned long nr_lock_classes; -static struct lock_class lock_classes[MAX_LOCKDEP_KEYS]; +struct lock_class lock_classes[MAX_LOCKDEP_KEYS]; static inline struct lock_class *hlock_class(struct held_lock *hlock) { @@ -1391,7 +1391,9 @@ static void print_lock_class_header(struct lock_class *class, int depth) printk("%*s->", depth, ""); print_lock_name(class); - printk(KERN_CONT " ops: %lu", class->ops); +#ifdef CONFIG_DEBUG_LOCKDEP + printk(KERN_CONT " ops: %lu", debug_class_ops_read(class)); +#endif printk(KERN_CONT " {\n"); for (bit = 0; bit < LOCK_USAGE_STATES; bit++) { @@ -2148,76 +2150,6 @@ static int check_no_collision(struct task_struct *curr, } /* - * This is for building a chain between just two different classes, - * instead of adding a new hlock upon current, which is done by - * add_chain_cache(). - * - * This can be called in any context with two classes, while - * add_chain_cache() must be done within the lock owener's context - * since it uses hlock which might be racy in another context. - */ -static inline int add_chain_cache_classes(unsigned int prev, - unsigned int next, - unsigned int irq_context, - u64 chain_key) -{ - struct hlist_head *hash_head = chainhashentry(chain_key); - struct lock_chain *chain; - - /* - * Allocate a new chain entry from the static array, and add - * it to the hash: - */ - - /* - * We might need to take the graph lock, ensure we've got IRQs - * disabled to make this an IRQ-safe lock.. for recursion reasons - * lockdep won't complain about its own locking errors. - */ - if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) - return 0; - - if (unlikely(nr_lock_chains >= MAX_LOCKDEP_CHAINS)) { - if (!debug_locks_off_graph_unlock()) - return 0; - - print_lockdep_off("BUG: MAX_LOCKDEP_CHAINS too low!"); - dump_stack(); - return 0; - } - - chain = lock_chains + nr_lock_chains++; - chain->chain_key = chain_key; - chain->irq_context = irq_context; - chain->depth = 2; - if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) { - chain->base = nr_chain_hlocks; - nr_chain_hlocks += chain->depth; - chain_hlocks[chain->base] = prev - 1; - chain_hlocks[chain->base + 1] = next -1; - } -#ifdef CONFIG_DEBUG_LOCKDEP - /* - * Important for check_no_collision(). - */ - else { - if (!debug_locks_off_graph_unlock()) - return 0; - - print_lockdep_off("BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!"); - dump_stack(); - return 0; - } -#endif - - hlist_add_head_rcu(&chain->entry, hash_head); - debug_atomic_inc(chain_lookup_misses); - inc_chains(); - - return 1; -} - -/* * Adds a dependency chain into chain hashtable. And must be called with * graph_lock held. * @@ -3262,6 +3194,10 @@ static int __lock_is_held(const struct lockdep_map *lock, int read); /* * This gets called for every mutex_lock*()/spin_lock*() operation. * We maintain the dependency maps and validate the locking attempt: + * + * The callers must make sure that IRQs are disabled before calling it, + * otherwise we could get an interrupt which would want to take locks, + * which would end up in lockdep again. */ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, int trylock, int read, int check, int hardirqs_off, @@ -3279,14 +3215,6 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, if (unlikely(!debug_locks)) return 0; - /* - * Lockdep should run with IRQs disabled, otherwise we could - * get an interrupt which would want to take locks, which would - * end up in lockdep and have you got a head-ache already? - */ - if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) - return 0; - if (!prove_locking || lock->key == &__lockdep_no_validate__) check = 0; @@ -3300,7 +3228,9 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, if (!class) return 0; } - atomic_inc((atomic_t *)&class->ops); + + debug_class_ops_inc(class); + if (very_verbose(class)) { printk("\nacquire class [%px] %s", class->key, class->name); if (class->name_version > 1) @@ -3543,6 +3473,9 @@ static int reacquire_held_locks(struct task_struct *curr, unsigned int depth, { struct held_lock *hlock; + if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) + return 0; + for (hlock = curr->held_locks + idx; idx < depth; idx++, hlock++) { if (!__lock_acquire(hlock->instance, hlock_class(hlock)->subclass, @@ -3696,6 +3629,13 @@ __lock_release(struct lockdep_map *lock, int nested, unsigned long ip) curr->lockdep_depth = i; curr->curr_chain_key = hlock->prev_chain_key; + /* + * The most likely case is when the unlock is on the innermost + * lock. In this case, we are done! + */ + if (i == depth-1) + return 1; + if (reacquire_held_locks(curr, depth, i + 1)) return 0; @@ -3703,10 +3643,14 @@ __lock_release(struct lockdep_map *lock, int nested, unsigned long ip) * We had N bottles of beer on the wall, we drank one, but now * there's not N-1 bottles of beer left on the wall... */ - if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - 1)) - return 0; + DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth-1); - return 1; + /* + * Since reacquire_held_locks() would have called check_chain_key() + * indirectly via __lock_acquire(), we don't need to do it again + * on return. + */ + return 0; } static int __lock_is_held(const struct lockdep_map *lock, int read) @@ -4122,7 +4066,7 @@ void lock_contended(struct lockdep_map *lock, unsigned long ip) { unsigned long flags; - if (unlikely(!lock_stat)) + if (unlikely(!lock_stat || !debug_locks)) return; if (unlikely(current->lockdep_recursion)) @@ -4142,7 +4086,7 @@ void lock_acquired(struct lockdep_map *lock, unsigned long ip) { unsigned long flags; - if (unlikely(!lock_stat)) + if (unlikely(!lock_stat || !debug_locks)) return; if (unlikely(current->lockdep_recursion)) diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h index d459d624ba2a..88c847a41c8a 100644 --- a/kernel/locking/lockdep_internals.h +++ b/kernel/locking/lockdep_internals.h @@ -152,9 +152,15 @@ struct lockdep_stats { int nr_find_usage_forwards_recursions; int nr_find_usage_backwards_checks; int nr_find_usage_backwards_recursions; + + /* + * Per lock class locking operation stat counts + */ + unsigned long lock_class_ops[MAX_LOCKDEP_KEYS]; }; DECLARE_PER_CPU(struct lockdep_stats, lockdep_stats); +extern struct lock_class lock_classes[MAX_LOCKDEP_KEYS]; #define __debug_atomic_inc(ptr) \ this_cpu_inc(lockdep_stats.ptr); @@ -179,9 +185,30 @@ DECLARE_PER_CPU(struct lockdep_stats, lockdep_stats); } \ __total; \ }) + +static inline void debug_class_ops_inc(struct lock_class *class) +{ + int idx; + + idx = class - lock_classes; + __debug_atomic_inc(lock_class_ops[idx]); +} + +static inline unsigned long debug_class_ops_read(struct lock_class *class) +{ + int idx, cpu; + unsigned long ops = 0; + + idx = class - lock_classes; + for_each_possible_cpu(cpu) + ops += per_cpu(lockdep_stats.lock_class_ops[idx], cpu); + return ops; +} + #else # define __debug_atomic_inc(ptr) do { } while (0) # define debug_atomic_inc(ptr) do { } while (0) # define debug_atomic_dec(ptr) do { } while (0) # define debug_atomic_read(ptr) 0 +# define debug_class_ops_inc(ptr) do { } while (0) #endif diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c index 3dd980dfba2d..3d31f9b0059e 100644 --- a/kernel/locking/lockdep_proc.c +++ b/kernel/locking/lockdep_proc.c @@ -68,7 +68,7 @@ static int l_show(struct seq_file *m, void *v) seq_printf(m, "%p", class->key); #ifdef CONFIG_DEBUG_LOCKDEP - seq_printf(m, " OPS:%8ld", class->ops); + seq_printf(m, " OPS:%8ld", debug_class_ops_read(class)); #endif #ifdef CONFIG_PROVE_LOCKING seq_printf(m, " FD:%5ld", lockdep_count_forward_deps(class)); diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index bfaeb05123ff..8a8c3c208c5e 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -74,12 +74,24 @@ */ #include "mcs_spinlock.h" +#define MAX_NODES 4 +/* + * On 64-bit architectures, the mcs_spinlock structure will be 16 bytes in + * size and four of them will fit nicely in one 64-byte cacheline. For + * pvqspinlock, however, we need more space for extra data. To accommodate + * that, we insert two more long words to pad it up to 32 bytes. IOW, only + * two of them can fit in a cacheline in this case. That is OK as it is rare + * to have more than 2 levels of slowpath nesting in actual use. We don't + * want to penalize pvqspinlocks to optimize for a rare case in native + * qspinlocks. + */ +struct qnode { + struct mcs_spinlock mcs; #ifdef CONFIG_PARAVIRT_SPINLOCKS -#define MAX_NODES 8 -#else -#define MAX_NODES 4 + long reserved[2]; #endif +}; /* * The pending bit spinning loop count. @@ -101,7 +113,7 @@ * * PV doubles the storage and uses the second cacheline for PV state. */ -static DEFINE_PER_CPU_ALIGNED(struct mcs_spinlock, mcs_nodes[MAX_NODES]); +static DEFINE_PER_CPU_ALIGNED(struct qnode, qnodes[MAX_NODES]); /* * We must be able to distinguish between no-tail and the tail at 0:0, @@ -126,7 +138,13 @@ static inline __pure 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); + return per_cpu_ptr(&qnodes[idx].mcs, cpu); +} + +static inline __pure +struct mcs_spinlock *grab_mcs_node(struct mcs_spinlock *base, int idx) +{ + return &((struct qnode *)base + idx)->mcs; } #define _Q_LOCKED_PENDING_MASK (_Q_LOCKED_MASK | _Q_PENDING_MASK) @@ -232,6 +250,20 @@ static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail) #endif /* _Q_PENDING_BITS == 8 */ /** + * queued_fetch_set_pending_acquire - fetch the whole lock value and set pending + * @lock : Pointer to queued spinlock structure + * Return: The previous lock value + * + * *,*,* -> *,1,* + */ +#ifndef queued_fetch_set_pending_acquire +static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lock) +{ + return atomic_fetch_or_acquire(_Q_PENDING_VAL, &lock->val); +} +#endif + +/** * set_locked - Set the lock bit and own the lock * @lock: Pointer to queued spinlock structure * @@ -326,43 +358,48 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) /* * trylock || pending * - * 0,0,0 -> 0,0,1 ; trylock - * 0,0,1 -> 0,1,1 ; pending + * 0,0,* -> 0,1,* -> 0,0,1 pending, trylock */ - val = atomic_fetch_or_acquire(_Q_PENDING_VAL, &lock->val); - if (!(val & ~_Q_LOCKED_MASK)) { - /* - * 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. - */ - if (val & _Q_LOCKED_MASK) { - atomic_cond_read_acquire(&lock->val, - !(VAL & _Q_LOCKED_MASK)); - } + val = queued_fetch_set_pending_acquire(lock); - /* - * take ownership and clear the pending bit. - * - * *,1,0 -> *,0,1 - */ - clear_pending_set_locked(lock); - qstat_inc(qstat_lock_pending, true); - return; + /* + * If we observe contention, there is a concurrent locker. + * + * Undo and queue; our setting of PENDING might have made the + * n,0,0 -> 0,0,0 transition fail and it will now be waiting + * on @next to become !NULL. + */ + if (unlikely(val & ~_Q_LOCKED_MASK)) { + + /* Undo PENDING if we set it. */ + if (!(val & _Q_PENDING_MASK)) + clear_pending(lock); + + goto queue; } /* - * If pending was clear but there are waiters in the queue, then - * we need to undo our setting of pending before we queue ourselves. + * We're pending, wait for the owner to go away. + * + * 0,1,1 -> 0,1,0 + * + * 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. + */ + if (val & _Q_LOCKED_MASK) + atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_MASK)); + + /* + * take ownership and clear the pending bit. + * + * 0,1,0 -> 0,0,1 */ - if (!(val & _Q_PENDING_MASK)) - clear_pending(lock); + clear_pending_set_locked(lock); + qstat_inc(qstat_lock_pending, true); + return; /* * End of pending bit optimistic spinning and beginning of MCS @@ -371,11 +408,16 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) queue: qstat_inc(qstat_lock_slowpath, true); pv_queue: - node = this_cpu_ptr(&mcs_nodes[0]); + node = this_cpu_ptr(&qnodes[0].mcs); idx = node->count++; tail = encode_tail(smp_processor_id(), idx); - node += idx; + node = grab_mcs_node(node, idx); + + /* + * Keep counts of non-zero index values: + */ + qstat_inc(qstat_lock_idx1 + idx - 1, idx); /* * Ensure that we increment the head node->count before initialising @@ -476,16 +518,25 @@ locked: */ /* - * In the PV case we might already have _Q_LOCKED_VAL set. + * In the PV case we might already have _Q_LOCKED_VAL set, because + * of lock stealing; therefore we must also allow: + * + * n,0,1 -> 0,0,1 * - * The atomic_cond_read_acquire() call above has provided the - * necessary acquire semantics required for locking. + * Note: at this point: (val & _Q_PENDING_MASK) == 0, because of the + * above wait condition, therefore any concurrent setting of + * PENDING will make the uncontended transition fail. */ - if (((val & _Q_TAIL_MASK) == tail) && - atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL)) - goto release; /* No contention */ + if ((val & _Q_TAIL_MASK) == tail) { + if (atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL)) + goto release; /* No contention */ + } - /* Either somebody is queued behind us or _Q_PENDING_VAL is set */ + /* + * Either somebody is queued behind us or _Q_PENDING_VAL got set + * which will then detect the remaining tail and queue behind us + * ensuring we'll see a @next. + */ set_locked(lock); /* @@ -501,7 +552,7 @@ release: /* * release the node */ - __this_cpu_dec(mcs_nodes[0].count); + __this_cpu_dec(qnodes[0].mcs.count); } EXPORT_SYMBOL(queued_spin_lock_slowpath); diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h index 5a0cf5f9008c..0130e488ebfe 100644 --- a/kernel/locking/qspinlock_paravirt.h +++ b/kernel/locking/qspinlock_paravirt.h @@ -49,8 +49,6 @@ enum vcpu_state { struct pv_node { struct mcs_spinlock mcs; - struct mcs_spinlock __res[3]; - int cpu; u8 state; }; @@ -281,7 +279,7 @@ 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)); + BUILD_BUG_ON(sizeof(struct pv_node) > sizeof(struct qnode)); pn->cpu = smp_processor_id(); pn->state = vcpu_running; diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h index 6bd78c0740fc..42d3d8dc8f49 100644 --- a/kernel/locking/qspinlock_stat.h +++ b/kernel/locking/qspinlock_stat.h @@ -55,6 +55,9 @@ enum qlock_stats { qstat_pv_wait_node, qstat_lock_pending, qstat_lock_slowpath, + qstat_lock_idx1, + qstat_lock_idx2, + qstat_lock_idx3, qstat_num, /* Total number of statistical counters */ qstat_reset_cnts = qstat_num, }; @@ -82,6 +85,9 @@ static const char * const qstat_names[qstat_num + 1] = { [qstat_pv_wait_node] = "pv_wait_node", [qstat_lock_pending] = "lock_pending", [qstat_lock_slowpath] = "lock_slowpath", + [qstat_lock_idx1] = "lock_index1", + [qstat_lock_idx2] = "lock_index2", + [qstat_lock_idx3] = "lock_index3", [qstat_reset_cnts] = "reset_counters", }; diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 2823d4163a37..581edcc63c26 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1485,9 +1485,9 @@ void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass) __rt_mutex_lock(lock, subclass); } EXPORT_SYMBOL_GPL(rt_mutex_lock_nested); -#endif -#ifndef CONFIG_DEBUG_LOCK_ALLOC +#else /* !CONFIG_DEBUG_LOCK_ALLOC */ + /** * rt_mutex_lock - lock a rt_mutex * diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 3064c50e181e..09b180063ee1 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -180,7 +180,7 @@ static void __rwsem_mark_wake(struct rw_semaphore *sem, * but it gives the spinners an early indication that the * readers now have the lock. */ - rwsem_set_reader_owned(sem); + __rwsem_set_reader_owned(sem, waiter->task); } /* @@ -233,8 +233,19 @@ __rwsem_down_read_failed_common(struct rw_semaphore *sem, int state) waiter.type = RWSEM_WAITING_FOR_READ; raw_spin_lock_irq(&sem->wait_lock); - if (list_empty(&sem->wait_list)) + if (list_empty(&sem->wait_list)) { + /* + * In case the wait queue is empty and the lock isn't owned + * by a writer, this reader can exit the slowpath and return + * immediately as its RWSEM_ACTIVE_READ_BIAS has already + * been set in the count. + */ + if (atomic_long_read(&sem->count) >= 0) { + raw_spin_unlock_irq(&sem->wait_lock); + return sem; + } adjustment += RWSEM_WAITING_BIAS; + } list_add_tail(&waiter.list, &sem->wait_list); /* we're now waiting on the lock, but no longer actively locking */ diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 776308d2fa9e..e586f0d03ad3 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -117,8 +117,9 @@ EXPORT_SYMBOL(down_write_trylock); void up_read(struct rw_semaphore *sem) { rwsem_release(&sem->dep_map, 1, _RET_IP_); - DEBUG_RWSEMS_WARN_ON(sem->owner != RWSEM_READER_OWNED); + DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED)); + rwsem_clear_reader_owned(sem); __up_read(sem); } @@ -181,7 +182,7 @@ void down_read_non_owner(struct rw_semaphore *sem) might_sleep(); __down_read(sem); - rwsem_set_reader_owned(sem); + __rwsem_set_reader_owned(sem, NULL); } EXPORT_SYMBOL(down_read_non_owner); @@ -215,7 +216,7 @@ EXPORT_SYMBOL(down_write_killable_nested); void up_read_non_owner(struct rw_semaphore *sem) { - DEBUG_RWSEMS_WARN_ON(sem->owner != RWSEM_READER_OWNED); + DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED)); __up_read(sem); } diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h index b9d0e72aa80f..bad2bca0268b 100644 --- a/kernel/locking/rwsem.h +++ b/kernel/locking/rwsem.h @@ -1,24 +1,30 @@ /* SPDX-License-Identifier: GPL-2.0 */ /* - * The owner field of the rw_semaphore structure will be set to - * RWSEM_READER_OWNED when a reader grabs the lock. A writer will clear - * the owner field when it unlocks. A reader, on the other hand, will - * not touch the owner field when it unlocks. + * The least significant 2 bits of the owner value has the following + * meanings when set. + * - RWSEM_READER_OWNED (bit 0): The rwsem is owned by readers + * - RWSEM_ANONYMOUSLY_OWNED (bit 1): The rwsem is anonymously owned, + * i.e. the owner(s) cannot be readily determined. It can be reader + * owned or the owning writer is indeterminate. * - * In essence, the owner field now has the following 4 states: - * 1) 0 - * - lock is free or the owner hasn't set the field yet - * 2) RWSEM_READER_OWNED - * - lock is currently or previously owned by readers (lock is free - * or not set by owner yet) - * 3) RWSEM_ANONYMOUSLY_OWNED bit set with some other bits set as well - * - lock is owned by an anonymous writer, so spinning on the lock - * owner should be disabled. - * 4) Other non-zero value - * - a writer owns the lock and other writers can spin on the lock owner. + * When a writer acquires a rwsem, it puts its task_struct pointer + * into the owner field. It is cleared after an unlock. + * + * When a reader acquires a rwsem, it will also puts its task_struct + * pointer into the owner field with both the RWSEM_READER_OWNED and + * RWSEM_ANONYMOUSLY_OWNED bits set. On unlock, the owner field will + * largely be left untouched. So for a free or reader-owned rwsem, + * the owner value may contain information about the last reader that + * acquires the rwsem. The anonymous bit is set because that particular + * reader may or may not still own the lock. + * + * That information may be helpful in debugging cases where the system + * seems to hang on a reader owned rwsem especially if only one reader + * is involved. Ideally we would like to track all the readers that own + * a rwsem, but the overhead is simply too big. */ -#define RWSEM_ANONYMOUSLY_OWNED (1UL << 0) -#define RWSEM_READER_OWNED ((struct task_struct *)RWSEM_ANONYMOUSLY_OWNED) +#define RWSEM_READER_OWNED (1UL << 0) +#define RWSEM_ANONYMOUSLY_OWNED (1UL << 1) #ifdef CONFIG_DEBUG_RWSEMS # define DEBUG_RWSEMS_WARN_ON(c) DEBUG_LOCKS_WARN_ON(c) @@ -44,15 +50,26 @@ static inline void rwsem_clear_owner(struct rw_semaphore *sem) WRITE_ONCE(sem->owner, NULL); } +/* + * The task_struct pointer of the last owning reader will be left in + * the owner field. + * + * Note that the owner value just indicates the task has owned the rwsem + * previously, it may not be the real owner or one of the real owners + * anymore when that field is examined, so take it with a grain of salt. + */ +static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem, + struct task_struct *owner) +{ + unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED + | RWSEM_ANONYMOUSLY_OWNED; + + WRITE_ONCE(sem->owner, (struct task_struct *)val); +} + static inline void rwsem_set_reader_owned(struct rw_semaphore *sem) { - /* - * We check the owner value first to make sure that we will only - * do a write to the rwsem cacheline when it is really necessary - * to minimize cacheline contention. - */ - if (READ_ONCE(sem->owner) != RWSEM_READER_OWNED) - WRITE_ONCE(sem->owner, RWSEM_READER_OWNED); + __rwsem_set_reader_owned(sem, current); } /* @@ -72,6 +89,25 @@ static inline bool rwsem_has_anonymous_owner(struct task_struct *owner) { return (unsigned long)owner & RWSEM_ANONYMOUSLY_OWNED; } + +#ifdef CONFIG_DEBUG_RWSEMS +/* + * With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there + * is a task pointer in owner of a reader-owned rwsem, it will be the + * real owner or one of the real owners. The only exception is when the + * unlock is done by up_read_non_owner(). + */ +#define rwsem_clear_reader_owned rwsem_clear_reader_owned +static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem) +{ + unsigned long val = (unsigned long)current | RWSEM_READER_OWNED + | RWSEM_ANONYMOUSLY_OWNED; + if (READ_ONCE(sem->owner) == (struct task_struct *)val) + cmpxchg_relaxed((unsigned long *)&sem->owner, val, + RWSEM_READER_OWNED | RWSEM_ANONYMOUSLY_OWNED); +} +#endif + #else static inline void rwsem_set_owner(struct rw_semaphore *sem) { @@ -81,7 +117,18 @@ static inline void rwsem_clear_owner(struct rw_semaphore *sem) { } +static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem, + struct task_struct *owner) +{ +} + static inline void rwsem_set_reader_owned(struct rw_semaphore *sem) { } #endif + +#ifndef rwsem_clear_reader_owned +static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem) +{ +} +#endif diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c index 0be047dbd897..65a3b7e55b9f 100644 --- a/kernel/locking/test-ww_mutex.c +++ b/kernel/locking/test-ww_mutex.c @@ -260,7 +260,7 @@ static void test_cycle_work(struct work_struct *work) { struct test_cycle *cycle = container_of(work, typeof(*cycle), work); struct ww_acquire_ctx ctx; - int err; + int err, erra = 0; ww_acquire_init(&ctx, &ww_class); ww_mutex_lock(&cycle->a_mutex, &ctx); @@ -270,17 +270,19 @@ static void test_cycle_work(struct work_struct *work) err = ww_mutex_lock(cycle->b_mutex, &ctx); if (err == -EDEADLK) { + err = 0; ww_mutex_unlock(&cycle->a_mutex); ww_mutex_lock_slow(cycle->b_mutex, &ctx); - err = ww_mutex_lock(&cycle->a_mutex, &ctx); + erra = ww_mutex_lock(&cycle->a_mutex, &ctx); } if (!err) ww_mutex_unlock(cycle->b_mutex); - ww_mutex_unlock(&cycle->a_mutex); + if (!erra) + ww_mutex_unlock(&cycle->a_mutex); ww_acquire_fini(&ctx); - cycle->result = err; + cycle->result = err ?: erra; } static int __test_cycle(unsigned int nthreads) |