[PATCH 05/31] ntsync: Introduce NTSYNC_IOC_WAIT_ALL.

This is similar to NTSYNC_IOC_WAIT_ANY, but waits until all of the objects are simultaneously signaled, and then acquires all of them as a single atomic operation. Signed-off-by: Elizabeth Figura &lt;zfigura(a)codeweavers.com&gt; --- drivers/misc/ntsync.c | 242 ++++++++++++++++++++++++++++++++++-- include/uapi/linux/ntsync.h | 1 + 2 files changed, 235 insertions(+), 8 deletions(-) diff --git a/drivers/misc/ntsync.c b/drivers/misc/ntsync.c index 123af239f52e..e173774eea52 100644 --- a/drivers/misc/ntsync.c +++ b/drivers/misc/ntsync.c @@ -42,7 +42,34 @@ struct ntsync_obj { } sem; } u; + /* + * any_waiters is protected by the object lock, but all_waiters is + * protected by the device wait_all_lock. + */ struct list_head any_waiters; + struct list_head all_waiters; + + /* + * Hint describing how many tasks are queued on this object in a + * wait-all operation. + * + * Any time we do a wake, we may need to wake "all" waiters as well as + * "any" waiters. In order to atomically wake "all" waiters, we must + * lock all of the objects, and that means grabbing the wait_all_lock + * below (and, due to lock ordering rules, before locking this object). + * However, wait-all is a rare operation, and grabbing the wait-all + * lock for every wake would create unnecessary contention. + * Therefore we first check whether all_hint is zero, and, if it is, + * we skip trying to wake "all" waiters. + * + * This hint isn't protected by any lock. It might change during the + * course of a wake, but there's no meaningful race there; it's only a + * hint. + * + * Since wait requests must originate from user-space threads, we're + * limited here by PID_MAX_LIMIT, so there's no risk of overflow. + */ + atomic_t all_hint; }; struct ntsync_q_entry { @@ -63,14 +90,99 @@ struct ntsync_q { */ atomic_t signaled; + bool all; __u32 count; struct ntsync_q_entry entries[]; }; struct ntsync_device { + /* + * Wait-all operations must atomically grab all objects, and be totally + * ordered with respect to each other and wait-any operations. + * If one thread is trying to acquire several objects, another thread + * cannot touch the object at the same time. + * + * We achieve this by grabbing multiple object locks at the same time. + * However, this creates a lock ordering problem. To solve that problem, + * wait_all_lock is taken first whenever multiple objects must be locked + * at the same time. + */ + spinlock_t wait_all_lock; + struct file *file; }; +static bool is_signaled(struct ntsync_obj *obj, __u32 owner) +{ + lockdep_assert_held(&obj->lock); + + switch (obj->type) { + case NTSYNC_TYPE_SEM: + return !!obj->u.sem.count; + } + + WARN(1, "bad object type %#x\n", obj->type); + return false; +} + +/* + * "locked_obj" is an optional pointer to an object which is already locked and + * should not be locked again. This is necessary so that changing an object's + * state and waking it can be a single atomic operation. + */ +static void try_wake_all(struct ntsync_device *dev, struct ntsync_q *q, + struct ntsync_obj *locked_obj) +{ + __u32 count = q->count; + bool can_wake = true; + __u32 i; + + lockdep_assert_held(&dev->wait_all_lock); + if (locked_obj) + lockdep_assert_held(&locked_obj->lock); + + for (i = 0; i < count; i++) { + if (q->entries[i].obj != locked_obj) + spin_lock_nest_lock(&q->entries[i].obj->lock, &dev->wait_all_lock); + } + + for (i = 0; i < count; i++) { + if (!is_signaled(q->entries[i].obj, q->owner)) { + can_wake = false; + break; + } + } + + if (can_wake && atomic_cmpxchg(&q->signaled, -1, 0) == -1) { + for (i = 0; i < count; i++) { + struct ntsync_obj *obj = q->entries[i].obj; + + switch (obj->type) { + case NTSYNC_TYPE_SEM: + obj->u.sem.count--; + break; + } + } + wake_up_process(q->task); + } + + for (i = 0; i < count; i++) { + if (q->entries[i].obj != locked_obj) + spin_unlock(&q->entries[i].obj->lock); + } +} + +static void try_wake_all_obj(struct ntsync_device *dev, struct ntsync_obj *obj) +{ + struct ntsync_q_entry *entry; + + lockdep_assert_held(&dev->wait_all_lock); + lockdep_assert_held(&obj->lock); + + list_for_each_entry(entry, &obj->all_waiters, node) + try_wake_all(dev, entry->q, obj); +} + static void try_wake_any_sem(struct ntsync_obj *sem) { struct ntsync_q_entry *entry; @@ -110,6 +222,7 @@ static int post_sem_state(struct ntsync_obj *sem, __u32 count) static int ntsync_sem_post(struct ntsync_obj *sem, void __user *argp) { + struct ntsync_device *dev = sem->dev; __u32 __user *user_args = argp; __u32 prev_count; __u32 args; @@ -121,14 +234,29 @@ static int ntsync_sem_post(struct ntsync_obj *sem, void __user *argp) if (sem->type != NTSYNC_TYPE_SEM) return -EINVAL; - spin_lock(&sem->lock); + if (atomic_read(&sem->all_hint) > 0) { + spin_lock(&dev->wait_all_lock); + spin_lock_nest_lock(&sem->lock, &dev->wait_all_lock); - prev_count = sem->u.sem.count; - ret = post_sem_state(sem, args); - if (!ret) - try_wake_any_sem(sem); + prev_count = sem->u.sem.count; + ret = post_sem_state(sem, args); + if (!ret) { + try_wake_all_obj(dev, sem); + try_wake_any_sem(sem); + } - spin_unlock(&sem->lock); + spin_unlock(&sem->lock); + spin_unlock(&dev->wait_all_lock); + } else { + spin_lock(&sem->lock); + + prev_count = sem->u.sem.count; + ret = post_sem_state(sem, args); + if (!ret) + try_wake_any_sem(sem); + + spin_unlock(&sem->lock); + } if (!ret && put_user(prev_count, user_args)) ret = -EFAULT; @@ -181,6 +309,8 @@ static struct ntsync_obj *ntsync_alloc_obj(struct ntsync_device *dev, get_file(dev->file); spin_lock_init(&obj->lock); INIT_LIST_HEAD(&obj->any_waiters); + INIT_LIST_HEAD(&obj->all_waiters); + atomic_set(&obj->all_hint, 0); return obj; } @@ -285,7 +415,7 @@ static int ntsync_schedule(const struct ntsync_q *q, const struct ntsync_wait_ar * Allocate and initialize the ntsync_q structure, but do not queue us yet. */ static int setup_wait(struct ntsync_device *dev, - const struct ntsync_wait_args *args, + const struct ntsync_wait_args *args, bool all, struct ntsync_q **ret_q) { const __u32 count = args->count; @@ -309,6 +439,7 @@ static int setup_wait(struct ntsync_device *dev, q->task = current; q->owner = args->owner; atomic_set(&q->signaled, -1); + q->all = all; q->count = count; for (i = 0; i < count; i++) { @@ -318,6 +449,16 @@ static int setup_wait(struct ntsync_device *dev, if (!obj) goto err; + if (all) { + /* Check that the objects are all distinct. */ + for (j = 0; j < i; j++) { + if (obj == q->entries[j].obj) { + put_obj(obj); + goto err; + } + } + } + entry->obj = obj; entry->q = q; entry->index = i; @@ -353,7 +494,7 @@ static int ntsync_wait_any(struct ntsync_device *dev, void __user *argp) if (copy_from_user(&args, argp, sizeof(args))) return -EFAULT; - ret = setup_wait(dev, &args, &q); + ret = setup_wait(dev, &args, false, &q); if (ret < 0) return ret; @@ -415,6 +556,87 @@ static int ntsync_wait_any(struct ntsync_device *dev, void __user *argp) return ret; } +static int ntsync_wait_all(struct ntsync_device *dev, void __user *argp) +{ + struct ntsync_wait_args args; + struct ntsync_q *q; + int signaled; + __u32 i; + int ret; + + if (copy_from_user(&args, argp, sizeof(args))) + return -EFAULT; + + ret = setup_wait(dev, &args, true, &q); + if (ret < 0) + return ret; + + /* queue ourselves */ + + spin_lock(&dev->wait_all_lock); + + for (i = 0; i < args.count; i++) { + struct ntsync_q_entry *entry = &q->entries[i]; + struct ntsync_obj *obj = entry->obj; + + atomic_inc(&obj->all_hint); + + /* + * obj->all_waiters is protected by dev->wait_all_lock rather + * than obj->lock, so there is no need to acquire obj->lock + * here. + */ + list_add_tail(&entry->node, &obj->all_waiters); + } + + /* check if we are already signaled */ + + try_wake_all(dev, q, NULL); + + spin_unlock(&dev->wait_all_lock); + + /* sleep */ + + ret = ntsync_schedule(q, &args); + + /* and finally, unqueue */ + + spin_lock(&dev->wait_all_lock); + + for (i = 0; i < args.count; i++) { + struct ntsync_q_entry *entry = &q->entries[i]; + struct ntsync_obj *obj = entry->obj; + + /* + * obj->all_waiters is protected by dev->wait_all_lock rather + * than obj->lock, so there is no need to acquire it here. + */ + list_del(&entry->node); + + atomic_dec(&obj->all_hint); + + put_obj(obj); + } + + spin_unlock(&dev->wait_all_lock); + + signaled = atomic_read(&q->signaled); + if (signaled != -1) { + struct ntsync_wait_args __user *user_args = argp; + + /* even if we caught a signal, we need to communicate success */ + ret = 0; + + if (put_user(signaled, &user_args->index)) + ret = -EFAULT; + } else if (!ret) { + ret = -ETIMEDOUT; + } + + kfree(q); + return ret; +} + static int ntsync_char_open(struct inode *inode, struct file *file) { struct ntsync_device *dev; @@ -423,6 +645,8 @@ static int ntsync_char_open(struct inode *inode, struct file *file) if (!dev) return -ENOMEM; + spin_lock_init(&dev->wait_all_lock); + file->private_data = dev; dev->file = file; return nonseekable_open(inode, file); @@ -446,6 +670,8 @@ static long ntsync_char_ioctl(struct file *file, unsigned int cmd, switch (cmd) { case NTSYNC_IOC_CREATE_SEM: return ntsync_create_sem(dev, argp); + case NTSYNC_IOC_WAIT_ALL: + return ntsync_wait_all(dev, argp); case NTSYNC_IOC_WAIT_ANY: return ntsync_wait_any(dev, argp); default: diff --git a/include/uapi/linux/ntsync.h b/include/uapi/linux/ntsync.h index 9cd1dd05d971..524404f6aceb 100644 --- a/include/uapi/linux/ntsync.h +++ b/include/uapi/linux/ntsync.h @@ -29,6 +29,7 @@ struct ntsync_wait_args { #define NTSYNC_IOC_CREATE_SEM _IOWR('N', 0x80, struct ntsync_sem_args) #define NTSYNC_IOC_WAIT_ANY _IOWR('N', 0x82, struct ntsync_wait_args) +#define NTSYNC_IOC_WAIT_ALL _IOWR('N', 0x83, struct ntsync_wait_args) #define NTSYNC_IOC_SEM_POST _IOWR('N', 0x81, __u32) -- 2.43.0