futex.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/io_uring.h>

#include <uapi/linux/io_uring.h>

#include "../kernel/futex/futex.h"
#include "io_uring.h"
#include "alloc_cache.h"
#include "futex.h"

struct io_futex {
	struct file	*file;
	union {
		u32 __user			*uaddr;
		struct futex_waitv __user	*uwaitv;
	};
	unsigned long	futex_val;
	unsigned long	futex_mask;
	unsigned long	futexv_owned;
	u32		futex_flags;
	unsigned int	futex_nr;
	bool		futexv_unqueued;
};

struct io_futex_data {
	struct futex_q	q;
	struct io_kiocb	*req;
};

#define IO_FUTEX_ALLOC_CACHE_MAX	32

bool io_futex_cache_init(struct io_ring_ctx *ctx)
{
	return io_alloc_cache_init(&ctx->futex_cache, IO_FUTEX_ALLOC_CACHE_MAX,
				sizeof(struct io_futex_data), 0);
}

void io_futex_cache_free(struct io_ring_ctx *ctx)
{
	io_alloc_cache_free(&ctx->futex_cache, kfree);
}

static void __io_futex_complete(struct io_kiocb *req, io_tw_token_t tw)
{
	req->async_data = NULL;
	hlist_del_init(&req->hash_node);
	io_req_task_complete(req, tw);
}

static void io_futex_complete(struct io_kiocb *req, io_tw_token_t tw)
{
	struct io_ring_ctx *ctx = req->ctx;

	io_tw_lock(ctx, tw);
	io_cache_free(&ctx->futex_cache, req->async_data);
	__io_futex_complete(req, tw);
}

static void io_futexv_complete(struct io_kiocb *req, io_tw_token_t tw)
{
	struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);
	struct futex_vector *futexv = req->async_data;

	io_tw_lock(req->ctx, tw);

	if (!iof->futexv_unqueued) {
		int res;

		res = futex_unqueue_multiple(futexv, iof->futex_nr);
		if (res != -1)
			io_req_set_res(req, res, 0);
	}

	kfree(req->async_data);
	req->flags &= ~REQ_F_ASYNC_DATA;
	__io_futex_complete(req, tw);
}

static bool io_futexv_claim(struct io_futex *iof)
{
	if (test_bit(0, &iof->futexv_owned) ||
	    test_and_set_bit_lock(0, &iof->futexv_owned))
		return false;
	return true;
}

static bool __io_futex_cancel(struct io_kiocb *req)
{
	/* futex wake already done or in progress */
	if (req->opcode == IORING_OP_FUTEX_WAIT) {
		struct io_futex_data *ifd = req->async_data;

		if (!futex_unqueue(&ifd->q))
			return false;
		req->io_task_work.func = io_futex_complete;
	} else {
		struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);

		if (!io_futexv_claim(iof))
			return false;
		req->io_task_work.func = io_futexv_complete;
	}

	hlist_del_init(&req->hash_node);
	io_req_set_res(req, -ECANCELED, 0);
	io_req_task_work_add(req);
	return true;
}

int io_futex_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
		    unsigned int issue_flags)
{
	return io_cancel_remove(ctx, cd, issue_flags, &ctx->futex_list, __io_futex_cancel);
}

bool io_futex_remove_all(struct io_ring_ctx *ctx, struct io_uring_task *tctx,
			 bool cancel_all)
{
	return io_cancel_remove_all(ctx, tctx, &ctx->futex_list, cancel_all, __io_futex_cancel);
}

int io_futex_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
	struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);
	u32 flags;

	if (unlikely(sqe->len || sqe->futex_flags || sqe->buf_index ||
		     sqe->file_index))
		return -EINVAL;

	iof->uaddr = u64_to_user_ptr(READ_ONCE(sqe->addr));
	iof->futex_val = READ_ONCE(sqe->addr2);
	iof->futex_mask = READ_ONCE(sqe->addr3);
	flags = READ_ONCE(sqe->fd);

	if (flags & ~FUTEX2_VALID_MASK)
		return -EINVAL;

	iof->futex_flags = futex2_to_flags(flags);
	if (!futex_flags_valid(iof->futex_flags))
		return -EINVAL;

	if (!futex_validate_input(iof->futex_flags, iof->futex_val) ||
	    !futex_validate_input(iof->futex_flags, iof->futex_mask))
		return -EINVAL;

	return 0;
}

static void io_futex_wakev_fn(struct wake_q_head *wake_q, struct futex_q *q)
{
	struct io_kiocb *req = q->wake_data;
	struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);

	if (!io_futexv_claim(iof))
		return;
	if (unlikely(!__futex_wake_mark(q)))
		return;

	io_req_set_res(req, 0, 0);
	req->io_task_work.func = io_futexv_complete;
	io_req_task_work_add(req);
}

int io_futexv_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
	struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);
	struct futex_vector *futexv;
	int ret;

	/* No flags or mask supported for waitv */
	if (unlikely(sqe->fd || sqe->buf_index || sqe->file_index ||
		     sqe->addr2 || sqe->futex_flags || sqe->addr3))
		return -EINVAL;

	iof->uaddr = u64_to_user_ptr(READ_ONCE(sqe->addr));
	iof->futex_nr = READ_ONCE(sqe->len);
	if (!iof->futex_nr || iof->futex_nr > FUTEX_WAITV_MAX)
		return -EINVAL;

	futexv = kcalloc(iof->futex_nr, sizeof(*futexv), GFP_KERNEL);
	if (!futexv)
		return -ENOMEM;

	ret = futex_parse_waitv(futexv, iof->uwaitv, iof->futex_nr,
				io_futex_wakev_fn, req);
	if (ret) {
		kfree(futexv);
		return ret;
	}

	iof->futexv_owned = 0;
	iof->futexv_unqueued = 0;
	req->flags |= REQ_F_ASYNC_DATA;
	req->async_data = futexv;
	return 0;
}

static void io_futex_wake_fn(struct wake_q_head *wake_q, struct futex_q *q)
{
	struct io_futex_data *ifd = container_of(q, struct io_futex_data, q);
	struct io_kiocb *req = ifd->req;

	if (unlikely(!__futex_wake_mark(q)))
		return;

	io_req_set_res(req, 0, 0);
	req->io_task_work.func = io_futex_complete;
	io_req_task_work_add(req);
}

int io_futexv_wait(struct io_kiocb *req, unsigned int issue_flags)
{
	struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);
	struct futex_vector *futexv = req->async_data;
	struct io_ring_ctx *ctx = req->ctx;
	int ret, woken = -1;

	io_ring_submit_lock(ctx, issue_flags);

	ret = futex_wait_multiple_setup(futexv, iof->futex_nr, &woken);

	/*
	 * Error case, ret is < 0. Mark the request as failed.
	 */
	if (unlikely(ret < 0)) {
		io_ring_submit_unlock(ctx, issue_flags);
		req_set_fail(req);
		io_req_set_res(req, ret, 0);
		kfree(futexv);
		req->async_data = NULL;
		req->flags &= ~REQ_F_ASYNC_DATA;
		return IOU_OK;
	}

	/*
	 * 0 return means that we successfully setup the waiters, and that
	 * nobody triggered a wakeup while we were doing so. If the wakeup
	 * happened post setup, the task_work will be run post this issue and
	 * under the submission lock. 1 means We got woken while setting up,
	 * let that side do the completion. Note that
	 * futex_wait_multiple_setup() will have unqueued all the futexes in
	 * this case. Mark us as having done that already, since this is
	 * different from normal wakeup.
	 */
	if (!ret) {
		/*
		 * If futex_wait_multiple_setup() returns 0 for a
		 * successful setup, then the task state will not be
		 * runnable. This is fine for the sync syscall, as
		 * it'll be blocking unless we already got one of the
		 * futexes woken, but it obviously won't work for an
		 * async invocation. Mark us runnable again.
		 */
		__set_current_state(TASK_RUNNING);
		hlist_add_head(&req->hash_node, &ctx->futex_list);
	} else {
		iof->futexv_unqueued = 1;
		if (woken != -1)
			io_req_set_res(req, woken, 0);
	}

	io_ring_submit_unlock(ctx, issue_flags);
	return IOU_ISSUE_SKIP_COMPLETE;
}

int io_futex_wait(struct io_kiocb *req, unsigned int issue_flags)
{
	struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);
	struct io_ring_ctx *ctx = req->ctx;
	struct io_futex_data *ifd = NULL;
	struct futex_hash_bucket *hb;
	int ret;

	if (!iof->futex_mask) {
		ret = -EINVAL;
		goto done;
	}

	io_ring_submit_lock(ctx, issue_flags);
	ifd = io_cache_alloc(&ctx->futex_cache, GFP_NOWAIT);
	if (!ifd) {
		ret = -ENOMEM;
		goto done_unlock;
	}

	req->async_data = ifd;
	ifd->q = futex_q_init;
	ifd->q.bitset = iof->futex_mask;
	ifd->q.wake = io_futex_wake_fn;
	ifd->req = req;

	ret = futex_wait_setup(iof->uaddr, iof->futex_val, iof->futex_flags,
			       &ifd->q, &hb);
	if (!ret) {
		hlist_add_head(&req->hash_node, &ctx->futex_list);
		io_ring_submit_unlock(ctx, issue_flags);

		futex_queue(&ifd->q, hb, NULL);
		return IOU_ISSUE_SKIP_COMPLETE;
	}

done_unlock:
	io_ring_submit_unlock(ctx, issue_flags);
done:
	if (ret < 0)
		req_set_fail(req);
	io_req_set_res(req, ret, 0);
	kfree(ifd);
	return IOU_OK;
}

int io_futex_wake(struct io_kiocb *req, unsigned int issue_flags)
{
	struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);
	int ret;

	/*
	 * Strict flags - ensure that waking 0 futexes yields a 0 result.
	 * See commit 43adf8449510 ("futex: FLAGS_STRICT") for details.
	 */
	ret = futex_wake(iof->uaddr, FLAGS_STRICT | iof->futex_flags,
			 iof->futex_val, iof->futex_mask);
	if (ret < 0)
		req_set_fail(req);
	io_req_set_res(req, ret, 0);
	return IOU_OK;
}