// SPDX-License-Identifier: GPL-2.0
/*
 * Support for async notification of waitid
 */
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/compat.h>
#include <linux/io_uring.h>

#include <uapi/linux/io_uring.h>

#include "io_uring.h"
#include "cancel.h"
#include "waitid.h"
#include "../kernel/exit.h"

static void io_waitid_cb(struct io_tw_req tw_req, io_tw_token_t tw);

#define IO_WAITID_CANCEL_FLAG   BIT(31)
#define IO_WAITID_REF_MASK      GENMASK(30, 0)

struct io_waitid {
        struct file *file;
        int which;
        pid_t upid;
        int options;
        atomic_t refs;
        struct wait_queue_head *head;
        struct siginfo __user *infop;
        struct waitid_info info;
};

static void io_waitid_free(struct io_kiocb *req)
{
        struct io_waitid_async *iwa = req->async_data;

        put_pid(iwa->wo.wo_pid);
        io_req_async_data_free(req);
}

static bool io_waitid_compat_copy_si(struct io_waitid *iw, int signo)
{
        struct compat_siginfo __user *infop;
        bool ret;

        infop = (struct compat_siginfo __user *) iw->infop;

        if (!user_write_access_begin(infop, sizeof(*infop)))
                return false;

        unsafe_put_user(signo, &infop->si_signo, Efault);
        unsafe_put_user(0, &infop->si_errno, Efault);
        unsafe_put_user(iw->info.cause, &infop->si_code, Efault);
        unsafe_put_user(iw->info.pid, &infop->si_pid, Efault);
        unsafe_put_user(iw->info.uid, &infop->si_uid, Efault);
        unsafe_put_user(iw->info.status, &infop->si_status, Efault);
        ret = true;
done:
        user_write_access_end();
        return ret;
Efault:
        ret = false;
        goto done;
}

static bool io_waitid_copy_si(struct io_kiocb *req, int signo)
{
        struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
        bool ret;

        if (!iw->infop)
                return true;

        if (io_is_compat(req->ctx))
                return io_waitid_compat_copy_si(iw, signo);

        if (!user_write_access_begin(iw->infop, sizeof(*iw->infop)))
                return false;

        unsafe_put_user(signo, &iw->infop->si_signo, Efault);
        unsafe_put_user(0, &iw->infop->si_errno, Efault);
        unsafe_put_user(iw->info.cause, &iw->infop->si_code, Efault);
        unsafe_put_user(iw->info.pid, &iw->infop->si_pid, Efault);
        unsafe_put_user(iw->info.uid, &iw->infop->si_uid, Efault);
        unsafe_put_user(iw->info.status, &iw->infop->si_status, Efault);
        ret = true;
done:
        user_write_access_end();
        return ret;
Efault:
        ret = false;
        goto done;
}

static int io_waitid_finish(struct io_kiocb *req, int ret)
{
        int signo = 0;

        if (ret > 0) {
                signo = SIGCHLD;
                ret = 0;
        }

        if (!io_waitid_copy_si(req, signo))
                ret = -EFAULT;
        io_waitid_free(req);
        return ret;
}

static void io_waitid_remove_wq(struct io_kiocb *req)
{
        struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
        struct wait_queue_head *head;

        head = smp_load_acquire(&iw->head);
        if (head) {
                struct io_waitid_async *iwa = req->async_data;

                smp_store_release(&iw->head, NULL);
                spin_lock_irq(&head->lock);
                list_del_init(&iwa->wo.child_wait.entry);
                spin_unlock_irq(&head->lock);
        }
}

static void io_waitid_complete(struct io_kiocb *req, int ret)
{
        struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);

        /* anyone completing better be holding a reference */
        WARN_ON_ONCE(!(atomic_read(&iw->refs) & IO_WAITID_REF_MASK));

        lockdep_assert_held(&req->ctx->uring_lock);

        hlist_del_init(&req->hash_node);
        io_waitid_remove_wq(req);

        ret = io_waitid_finish(req, ret);
        if (ret < 0)
                req_set_fail(req);
        io_req_set_res(req, ret, 0);
}

static bool __io_waitid_cancel(struct io_kiocb *req)
{
        struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);

        lockdep_assert_held(&req->ctx->uring_lock);

        /*
         * Mark us canceled regardless of ownership. This will prevent a
         * potential retry from a spurious wakeup.
         */
        atomic_or(IO_WAITID_CANCEL_FLAG, &iw->refs);

        /* claim ownership */
        if (atomic_fetch_inc(&iw->refs) & IO_WAITID_REF_MASK)
                return false;

        io_waitid_complete(req, -ECANCELED);
        io_req_queue_tw_complete(req, -ECANCELED);
        return true;
}

int io_waitid_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
                     unsigned int issue_flags)
{
        return io_cancel_remove(ctx, cd, issue_flags, &ctx->waitid_list, __io_waitid_cancel);
}

bool io_waitid_remove_all(struct io_ring_ctx *ctx, struct io_uring_task *tctx,
                          bool cancel_all)
{
        return io_cancel_remove_all(ctx, tctx, &ctx->waitid_list, cancel_all, __io_waitid_cancel);
}

static inline bool io_waitid_drop_issue_ref(struct io_kiocb *req)
{
        struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);

        if (!atomic_sub_return(1, &iw->refs))
                return false;

        io_waitid_remove_wq(req);

        /*
         * Wakeup triggered, racing with us. It was prevented from
         * completing because of that, queue up the tw to do that.
         */
        req->io_task_work.func = io_waitid_cb;
        io_req_task_work_add(req);
        return true;
}

static void io_waitid_cb(struct io_tw_req tw_req, io_tw_token_t tw)
{
        struct io_kiocb *req = tw_req.req;
        struct io_waitid_async *iwa = req->async_data;
        struct io_ring_ctx *ctx = req->ctx;
        int ret;

        io_tw_lock(ctx, tw);

        ret = __do_wait(&iwa->wo);

        /*
         * If we get -ERESTARTSYS here, we need to re-arm and check again
         * to ensure we get another callback. If the retry works, then we can
         * just remove ourselves from the waitqueue again and finish the
         * request.
         */
        if (unlikely(ret == -ERESTARTSYS)) {
                struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);

                /* Don't retry if cancel found it meanwhile */
                ret = -ECANCELED;
                if (!(atomic_read(&iw->refs) & IO_WAITID_CANCEL_FLAG)) {
                        iw->head = &current->signal->wait_chldexit;
                        add_wait_queue(iw->head, &iwa->wo.child_wait);
                        ret = __do_wait(&iwa->wo);
                        if (ret == -ERESTARTSYS) {
                                /* retry armed, drop our ref */
                                io_waitid_drop_issue_ref(req);
                                return;
                        }
                        /* fall through to complete, will kill waitqueue */
                }
        }

        io_waitid_complete(req, ret);
        io_req_task_complete(tw_req, tw);
}

static int io_waitid_wait(struct wait_queue_entry *wait, unsigned mode,
                          int sync, void *key)
{
        struct wait_opts *wo = container_of(wait, struct wait_opts, child_wait);
        struct io_waitid_async *iwa = container_of(wo, struct io_waitid_async, wo);
        struct io_kiocb *req = iwa->req;
        struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
        struct task_struct *p = key;

        if (!pid_child_should_wake(wo, p))
                return 0;

        list_del_init(&wait->entry);
        smp_store_release(&iw->head, NULL);

        /* cancel is in progress */
        if (atomic_fetch_inc(&iw->refs) & IO_WAITID_REF_MASK)
                return 1;

        req->io_task_work.func = io_waitid_cb;
        io_req_task_work_add(req);
        return 1;
}

int io_waitid_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
        struct io_waitid_async *iwa;

        if (sqe->addr || sqe->buf_index || sqe->addr3 || sqe->waitid_flags)
                return -EINVAL;

        iwa = io_uring_alloc_async_data(NULL, req);
        if (unlikely(!iwa))
                return -ENOMEM;
        iwa->req = req;

        iw->which = READ_ONCE(sqe->len);
        iw->upid = READ_ONCE(sqe->fd);
        iw->options = READ_ONCE(sqe->file_index);
        iw->head = NULL;
        iw->infop = u64_to_user_ptr(READ_ONCE(sqe->addr2));
        return 0;
}

int io_waitid(struct io_kiocb *req, unsigned int issue_flags)
{
        struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
        struct io_waitid_async *iwa = req->async_data;
        struct io_ring_ctx *ctx = req->ctx;
        int ret;

        ret = kernel_waitid_prepare(&iwa->wo, iw->which, iw->upid, &iw->info,
                                        iw->options, NULL);
        if (ret)
                goto done;

        /*
         * Mark the request as busy upfront, in case we're racing with the
         * wakeup. If we are, then we'll notice when we drop this initial
         * reference again after arming.
         */
        atomic_set(&iw->refs, 1);

        /*
         * Cancel must hold the ctx lock, so there's no risk of cancelation
         * finding us until a) we remain on the list, and b) the lock is
         * dropped. We only need to worry about racing with the wakeup
         * callback.
         */
        io_ring_submit_lock(ctx, issue_flags);

        /*
         * iw->head is valid under the ring lock, and as long as the request
         * is on the waitid_list where cancelations may find it.
         */
        iw->head = &current->signal->wait_chldexit;
        hlist_add_head(&req->hash_node, &ctx->waitid_list);

        init_waitqueue_func_entry(&iwa->wo.child_wait, io_waitid_wait);
        iwa->wo.child_wait.private = req->tctx->task;
        add_wait_queue(iw->head, &iwa->wo.child_wait);

        ret = __do_wait(&iwa->wo);
        if (ret == -ERESTARTSYS) {
                /*
                 * Nobody else grabbed a reference, it'll complete when we get
                 * a waitqueue callback, or if someone cancels it.
                 */
                if (!io_waitid_drop_issue_ref(req)) {
                        io_ring_submit_unlock(ctx, issue_flags);
                        return IOU_ISSUE_SKIP_COMPLETE;
                }

                /*
                 * Wakeup triggered, racing with us. It was prevented from
                 * completing because of that, queue up the tw to do that.
                 */
                io_ring_submit_unlock(ctx, issue_flags);
                return IOU_ISSUE_SKIP_COMPLETE;
        }

        hlist_del_init(&req->hash_node);
        io_waitid_remove_wq(req);
        ret = io_waitid_finish(req, ret);

        io_ring_submit_unlock(ctx, issue_flags);
done:
        if (ret < 0)
                req_set_fail(req);
        io_req_set_res(req, ret, 0);
        return IOU_COMPLETE;
}