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// 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: 1;
struct rcu_head rcu;
atomic_t refs;
atomic_t ops;
};
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_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);
if (atomic_dec_and_test(&ev_fd->refs))
io_eventfd_free(rcu);
}
void io_eventfd_signal(struct io_ring_ctx *ctx)
{
struct io_ev_fd *ev_fd = NULL;
if (READ_ONCE(ctx->rings->cq_flags) & IORING_CQ_EVENTFD_DISABLED)
return;
guard(rcu)();
/*
* 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 incase 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 (unlikely(!ev_fd))
return;
if (!atomic_inc_not_zero(&ev_fd->refs))
return;
if (ev_fd->eventfd_async && !io_wq_current_is_worker())
goto out;
if (likely(eventfd_signal_allowed())) {
eventfd_signal_mask(ev_fd->cq_ev_fd, EPOLL_URING_WAKE);
} else {
if (!atomic_fetch_or(BIT(IO_EVENTFD_OP_SIGNAL_BIT), &ev_fd->ops)) {
call_rcu_hurry(&ev_fd->rcu, io_eventfd_do_signal);
return;
}
}
out:
if (atomic_dec_and_test(&ev_fd->refs))
call_rcu(&ev_fd->rcu, io_eventfd_free);
}
void io_eventfd_flush_signal(struct io_ring_ctx *ctx)
{
bool skip;
spin_lock(&ctx->completion_lock);
/*
* 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 depedency 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.
*/
skip = ctx->cached_cq_tail == ctx->evfd_last_cq_tail;
ctx->evfd_last_cq_tail = ctx->cached_cq_tail;
spin_unlock(&ctx->completion_lock);
if (skip)
return;
io_eventfd_signal(ctx);
}
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);
ctx->evfd_last_cq_tail = ctx->cached_cq_tail;
spin_unlock(&ctx->completion_lock);
ev_fd->eventfd_async = eventfd_async;
ctx->has_evfd = true;
atomic_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);
if (atomic_dec_and_test(&ev_fd->refs))
call_rcu(&ev_fd->rcu, io_eventfd_free);
return 0;
}
return -ENXIO;
}
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