diff options
Diffstat (limited to 'io_uring/eventfd.c')
| -rw-r--r-- | io_uring/eventfd.c | 206 |
1 files changed, 206 insertions, 0 deletions
diff --git a/io_uring/eventfd.c b/io_uring/eventfd.c new file mode 100644 index 000000000000..100d5da94cb9 --- /dev/null +++ b/io_uring/eventfd.c @@ -0,0 +1,206 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <linux/kernel.h> +#include <linux/errno.h> +#include <linux/mm.h> +#include <linux/slab.h> +#include <linux/eventfd.h> +#include <linux/eventpoll.h> +#include <linux/io_uring.h> +#include <linux/io_uring_types.h> + +#include "io-wq.h" +#include "eventfd.h" + +struct io_ev_fd { + struct eventfd_ctx *cq_ev_fd; + unsigned int eventfd_async; + /* protected by ->completion_lock */ + unsigned last_cq_tail; + refcount_t refs; + atomic_t ops; + struct rcu_head rcu; +}; + +enum { + IO_EVENTFD_OP_SIGNAL_BIT, +}; + +static void io_eventfd_free(struct rcu_head *rcu) +{ + struct io_ev_fd *ev_fd = container_of(rcu, struct io_ev_fd, rcu); + + eventfd_ctx_put(ev_fd->cq_ev_fd); + kfree(ev_fd); +} + +static void io_eventfd_put(struct io_ev_fd *ev_fd) +{ + if (refcount_dec_and_test(&ev_fd->refs)) + call_rcu(&ev_fd->rcu, io_eventfd_free); +} + +static void io_eventfd_do_signal(struct rcu_head *rcu) +{ + struct io_ev_fd *ev_fd = container_of(rcu, struct io_ev_fd, rcu); + + eventfd_signal_mask(ev_fd->cq_ev_fd, EPOLL_URING_WAKE); + io_eventfd_put(ev_fd); +} + +static void io_eventfd_release(struct io_ev_fd *ev_fd, bool put_ref) +{ + if (put_ref) + io_eventfd_put(ev_fd); + rcu_read_unlock(); +} + +/* + * Returns true if the caller should put the ev_fd reference, false if not. + */ +static bool __io_eventfd_signal(struct io_ev_fd *ev_fd) +{ + if (eventfd_signal_allowed()) { + eventfd_signal_mask(ev_fd->cq_ev_fd, EPOLL_URING_WAKE); + return true; + } + if (!atomic_fetch_or(BIT(IO_EVENTFD_OP_SIGNAL_BIT), &ev_fd->ops)) { + call_rcu_hurry(&ev_fd->rcu, io_eventfd_do_signal); + return false; + } + return true; +} + +/* + * Trigger if eventfd_async isn't set, or if it's set and the caller is + * an async worker. If ev_fd isn't valid, obviously return false. + */ +static bool io_eventfd_trigger(struct io_ev_fd *ev_fd) +{ + if (ev_fd) + return !ev_fd->eventfd_async || io_wq_current_is_worker(); + return false; +} + +/* + * On success, returns with an ev_fd reference grabbed and the RCU read + * lock held. + */ +static struct io_ev_fd *io_eventfd_grab(struct io_ring_ctx *ctx) +{ + struct io_ev_fd *ev_fd; + + if (READ_ONCE(ctx->rings->cq_flags) & IORING_CQ_EVENTFD_DISABLED) + return NULL; + + rcu_read_lock(); + + /* + * rcu_dereference ctx->io_ev_fd once and use it for both for checking + * and eventfd_signal + */ + ev_fd = rcu_dereference(ctx->io_ev_fd); + + /* + * Check again if ev_fd exists in case an io_eventfd_unregister call + * completed between the NULL check of ctx->io_ev_fd at the start of + * the function and rcu_read_lock. + */ + if (io_eventfd_trigger(ev_fd) && refcount_inc_not_zero(&ev_fd->refs)) + return ev_fd; + + rcu_read_unlock(); + return NULL; +} + +void io_eventfd_signal(struct io_ring_ctx *ctx) +{ + struct io_ev_fd *ev_fd; + + ev_fd = io_eventfd_grab(ctx); + if (ev_fd) + io_eventfd_release(ev_fd, __io_eventfd_signal(ev_fd)); +} + +void io_eventfd_flush_signal(struct io_ring_ctx *ctx) +{ + struct io_ev_fd *ev_fd; + + ev_fd = io_eventfd_grab(ctx); + if (ev_fd) { + bool skip, put_ref = true; + + /* + * Eventfd should only get triggered when at least one event + * has been posted. Some applications rely on the eventfd + * notification count only changing IFF a new CQE has been + * added to the CQ ring. There's no dependency on 1:1 + * relationship between how many times this function is called + * (and hence the eventfd count) and number of CQEs posted to + * the CQ ring. + */ + spin_lock(&ctx->completion_lock); + skip = ctx->cached_cq_tail == ev_fd->last_cq_tail; + ev_fd->last_cq_tail = ctx->cached_cq_tail; + spin_unlock(&ctx->completion_lock); + + if (!skip) + put_ref = __io_eventfd_signal(ev_fd); + + io_eventfd_release(ev_fd, put_ref); + } +} + +int io_eventfd_register(struct io_ring_ctx *ctx, void __user *arg, + unsigned int eventfd_async) +{ + struct io_ev_fd *ev_fd; + __s32 __user *fds = arg; + int fd; + + ev_fd = rcu_dereference_protected(ctx->io_ev_fd, + lockdep_is_held(&ctx->uring_lock)); + if (ev_fd) + return -EBUSY; + + if (copy_from_user(&fd, fds, sizeof(*fds))) + return -EFAULT; + + ev_fd = kmalloc(sizeof(*ev_fd), GFP_KERNEL); + if (!ev_fd) + return -ENOMEM; + + ev_fd->cq_ev_fd = eventfd_ctx_fdget(fd); + if (IS_ERR(ev_fd->cq_ev_fd)) { + int ret = PTR_ERR(ev_fd->cq_ev_fd); + + kfree(ev_fd); + return ret; + } + + spin_lock(&ctx->completion_lock); + ev_fd->last_cq_tail = ctx->cached_cq_tail; + spin_unlock(&ctx->completion_lock); + + ev_fd->eventfd_async = eventfd_async; + ctx->has_evfd = true; + refcount_set(&ev_fd->refs, 1); + atomic_set(&ev_fd->ops, 0); + rcu_assign_pointer(ctx->io_ev_fd, ev_fd); + return 0; +} + +int io_eventfd_unregister(struct io_ring_ctx *ctx) +{ + struct io_ev_fd *ev_fd; + + ev_fd = rcu_dereference_protected(ctx->io_ev_fd, + lockdep_is_held(&ctx->uring_lock)); + if (ev_fd) { + ctx->has_evfd = false; + rcu_assign_pointer(ctx->io_ev_fd, NULL); + io_eventfd_put(ev_fd); + return 0; + } + + return -ENXIO; +} |