Merge tag 'pull-misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

[thirdparty/kernel/linux.git] / io_uring / rw.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/blk-mq.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/fsnotify.h>
#include <linux/poll.h>
#include <linux/nospec.h>
#include <linux/compat.h>
#include <linux/io_uring/cmd.h>
#include <linux/indirect_call_wrapper.h>

#include <uapi/linux/io_uring.h>

#include "io_uring.h"
#include "opdef.h"
#include "kbuf.h"
#include "alloc_cache.h"
#include "rsrc.h"
#include "poll.h"
#include "rw.h"

struct io_rw {
        /* NOTE: kiocb has the file as the first member, so don't do it here */
        struct kiocb                    kiocb;
        u64                             addr;
        u32                             len;
        rwf_t                           flags;
};

static inline bool io_file_supports_nowait(struct io_kiocb *req)
{
        return req->flags & REQ_F_SUPPORT_NOWAIT;
}

#ifdef CONFIG_COMPAT
static int io_iov_compat_buffer_select_prep(struct io_rw *rw)
{
        struct compat_iovec __user *uiov;
        compat_ssize_t clen;

        uiov = u64_to_user_ptr(rw->addr);
        if (!access_ok(uiov, sizeof(*uiov)))
                return -EFAULT;
        if (__get_user(clen, &uiov->iov_len))
                return -EFAULT;
        if (clen < 0)
                return -EINVAL;

        rw->len = clen;
        return 0;
}
#endif

static int io_iov_buffer_select_prep(struct io_kiocb *req)
{
        struct iovec __user *uiov;
        struct iovec iov;
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);

        if (rw->len != 1)
                return -EINVAL;

#ifdef CONFIG_COMPAT
        if (req->ctx->compat)
                return io_iov_compat_buffer_select_prep(rw);
#endif

        uiov = u64_to_user_ptr(rw->addr);
        if (copy_from_user(&iov, uiov, sizeof(*uiov)))
                return -EFAULT;
        rw->len = iov.iov_len;
        return 0;
}

static int __io_import_iovec(int ddir, struct io_kiocb *req,
                             struct io_async_rw *io,
                             unsigned int issue_flags)
{
        const struct io_issue_def *def = &io_issue_defs[req->opcode];
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
        struct iovec *iov;
        void __user *buf;
        int nr_segs, ret;
        size_t sqe_len;

        buf = u64_to_user_ptr(rw->addr);
        sqe_len = rw->len;

        if (!def->vectored || req->flags & REQ_F_BUFFER_SELECT) {
                if (io_do_buffer_select(req)) {
                        buf = io_buffer_select(req, &sqe_len, issue_flags);
                        if (!buf)
                                return -ENOBUFS;
                        rw->addr = (unsigned long) buf;
                        rw->len = sqe_len;
                }

                return import_ubuf(ddir, buf, sqe_len, &io->iter);
        }

        if (io->free_iovec) {
                nr_segs = io->free_iov_nr;
                iov = io->free_iovec;
        } else {
                iov = &io->fast_iov;
                nr_segs = 1;
        }
        ret = __import_iovec(ddir, buf, sqe_len, nr_segs, &iov, &io->iter,
                                req->ctx->compat);
        if (unlikely(ret < 0))
                return ret;
        if (iov) {
                req->flags |= REQ_F_NEED_CLEANUP;
                io->free_iov_nr = io->iter.nr_segs;
                kfree(io->free_iovec);
                io->free_iovec = iov;
        }
        return 0;
}

static inline int io_import_iovec(int rw, struct io_kiocb *req,
                                  struct io_async_rw *io,
                                  unsigned int issue_flags)
{
        int ret;

        ret = __io_import_iovec(rw, req, io, issue_flags);
        if (unlikely(ret < 0))
                return ret;

        iov_iter_save_state(&io->iter, &io->iter_state);
        return 0;
}

static void io_rw_iovec_free(struct io_async_rw *rw)
{
        if (rw->free_iovec) {
                kfree(rw->free_iovec);
                rw->free_iov_nr = 0;
                rw->free_iovec = NULL;
        }
}

static void io_rw_recycle(struct io_kiocb *req, unsigned int issue_flags)
{
        struct io_async_rw *rw = req->async_data;
        struct iovec *iov;

        if (unlikely(issue_flags & IO_URING_F_UNLOCKED)) {
                io_rw_iovec_free(rw);
                return;
        }
        iov = rw->free_iovec;
        if (io_alloc_cache_put(&req->ctx->rw_cache, rw)) {
                if (iov)
                        kasan_mempool_poison_object(iov);
                req->async_data = NULL;
                req->flags &= ~REQ_F_ASYNC_DATA;
        }
}

static void io_req_rw_cleanup(struct io_kiocb *req, unsigned int issue_flags)
{
        /*
         * Disable quick recycling for anything that's gone through io-wq.
         * In theory, this should be fine to cleanup. However, some read or
         * write iter handling touches the iovec AFTER having called into the
         * handler, eg to reexpand or revert. This means we can have:
         *
         * task                 io-wq
         *   issue
         *     punt to io-wq
         *                      issue
         *                        blkdev_write_iter()
         *                          ->ki_complete()
         *                            io_complete_rw()
         *                              queue tw complete
         *  run tw
         *    req_rw_cleanup
         *                      iov_iter_count() <- look at iov_iter again
         *
         * which can lead to a UAF. This is only possible for io-wq offload
         * as the cleanup can run in parallel. As io-wq is not the fast path,
         * just leave cleanup to the end.
         *
         * This is really a bug in the core code that does this, any issue
         * path should assume that a successful (or -EIOCBQUEUED) return can
         * mean that the underlying data can be gone at any time. But that
         * should be fixed seperately, and then this check could be killed.
         */
        if (!(req->flags & REQ_F_REFCOUNT)) {
                req->flags &= ~REQ_F_NEED_CLEANUP;
                io_rw_recycle(req, issue_flags);
        }
}

static int io_rw_alloc_async(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_async_rw *rw;

        rw = io_alloc_cache_get(&ctx->rw_cache);
        if (rw) {
                if (rw->free_iovec) {
                        kasan_mempool_unpoison_object(rw->free_iovec,
                                rw->free_iov_nr * sizeof(struct iovec));
                        req->flags |= REQ_F_NEED_CLEANUP;
                }
                req->flags |= REQ_F_ASYNC_DATA;
                req->async_data = rw;
                goto done;
        }

        if (!io_alloc_async_data(req)) {
                rw = req->async_data;
                rw->free_iovec = NULL;
                rw->free_iov_nr = 0;
done:
                rw->bytes_done = 0;
                return 0;
        }

        return -ENOMEM;
}

static int io_prep_rw_setup(struct io_kiocb *req, int ddir, bool do_import)
{
        struct io_async_rw *rw;
        int ret;

        if (io_rw_alloc_async(req))
                return -ENOMEM;

        if (!do_import || io_do_buffer_select(req))
                return 0;

        rw = req->async_data;
        ret = io_import_iovec(ddir, req, rw, 0);
        if (unlikely(ret < 0))
                return ret;

        iov_iter_save_state(&rw->iter, &rw->iter_state);
        return 0;
}

static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
                      int ddir, bool do_import)
{
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
        unsigned ioprio;
        int ret;

        rw->kiocb.ki_pos = READ_ONCE(sqe->off);
        /* used for fixed read/write too - just read unconditionally */
        req->buf_index = READ_ONCE(sqe->buf_index);

        ioprio = READ_ONCE(sqe->ioprio);
        if (ioprio) {
                ret = ioprio_check_cap(ioprio);
                if (ret)
                        return ret;

                rw->kiocb.ki_ioprio = ioprio;
        } else {
                rw->kiocb.ki_ioprio = get_current_ioprio();
        }
        rw->kiocb.dio_complete = NULL;

        rw->addr = READ_ONCE(sqe->addr);
        rw->len = READ_ONCE(sqe->len);
        rw->flags = READ_ONCE(sqe->rw_flags);
        return io_prep_rw_setup(req, ddir, do_import);
}

int io_prep_read(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        return io_prep_rw(req, sqe, ITER_DEST, true);
}

int io_prep_write(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        return io_prep_rw(req, sqe, ITER_SOURCE, true);
}

static int io_prep_rwv(struct io_kiocb *req, const struct io_uring_sqe *sqe,
                       int ddir)
{
        const bool do_import = !(req->flags & REQ_F_BUFFER_SELECT);
        int ret;

        ret = io_prep_rw(req, sqe, ddir, do_import);
        if (unlikely(ret))
                return ret;
        if (do_import)
                return 0;

        /*
         * Have to do this validation here, as this is in io_read() rw->len
         * might have chanaged due to buffer selection
         */
        return io_iov_buffer_select_prep(req);
}

int io_prep_readv(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        return io_prep_rwv(req, sqe, ITER_DEST);
}

int io_prep_writev(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        return io_prep_rwv(req, sqe, ITER_SOURCE);
}

static int io_prep_rw_fixed(struct io_kiocb *req, const struct io_uring_sqe *sqe,
                            int ddir)
{
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
        struct io_ring_ctx *ctx = req->ctx;
        struct io_async_rw *io;
        u16 index;
        int ret;

        ret = io_prep_rw(req, sqe, ddir, false);
        if (unlikely(ret))
                return ret;

        if (unlikely(req->buf_index >= ctx->nr_user_bufs))
                return -EFAULT;
        index = array_index_nospec(req->buf_index, ctx->nr_user_bufs);
        req->imu = ctx->user_bufs[index];
        io_req_set_rsrc_node(req, ctx, 0);

        io = req->async_data;
        ret = io_import_fixed(ddir, &io->iter, req->imu, rw->addr, rw->len);
        iov_iter_save_state(&io->iter, &io->iter_state);
        return ret;
}

int io_prep_read_fixed(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        return io_prep_rw_fixed(req, sqe, ITER_DEST);
}

int io_prep_write_fixed(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        return io_prep_rw_fixed(req, sqe, ITER_SOURCE);
}

/*
 * Multishot read is prepared just like a normal read/write request, only
 * difference is that we set the MULTISHOT flag.
 */
int io_read_mshot_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
        int ret;

        /* must be used with provided buffers */
        if (!(req->flags & REQ_F_BUFFER_SELECT))
                return -EINVAL;

        ret = io_prep_rw(req, sqe, ITER_DEST, false);
        if (unlikely(ret))
                return ret;

        if (rw->addr || rw->len)
                return -EINVAL;

        req->flags |= REQ_F_APOLL_MULTISHOT;
        return 0;
}

void io_readv_writev_cleanup(struct io_kiocb *req)
{
        io_rw_iovec_free(req->async_data);
}

static inline loff_t *io_kiocb_update_pos(struct io_kiocb *req)
{
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);

        if (rw->kiocb.ki_pos != -1)
                return &rw->kiocb.ki_pos;

        if (!(req->file->f_mode & FMODE_STREAM)) {
                req->flags |= REQ_F_CUR_POS;
                rw->kiocb.ki_pos = req->file->f_pos;
                return &rw->kiocb.ki_pos;
        }

        rw->kiocb.ki_pos = 0;
        return NULL;
}

#ifdef CONFIG_BLOCK
static void io_resubmit_prep(struct io_kiocb *req)
{
        struct io_async_rw *io = req->async_data;

        iov_iter_restore(&io->iter, &io->iter_state);
}

static bool io_rw_should_reissue(struct io_kiocb *req)
{
        umode_t mode = file_inode(req->file)->i_mode;
        struct io_ring_ctx *ctx = req->ctx;

        if (!S_ISBLK(mode) && !S_ISREG(mode))
                return false;
        if ((req->flags & REQ_F_NOWAIT) || (io_wq_current_is_worker() &&
            !(ctx->flags & IORING_SETUP_IOPOLL)))
                return false;
        /*
         * If ref is dying, we might be running poll reap from the exit work.
         * Don't attempt to reissue from that path, just let it fail with
         * -EAGAIN.
         */
        if (percpu_ref_is_dying(&ctx->refs))
                return false;
        /*
         * Play it safe and assume not safe to re-import and reissue if we're
         * not in the original thread group (or in task context).
         */
        if (!same_thread_group(req->task, current) || !in_task())
                return false;
        return true;
}
#else
static void io_resubmit_prep(struct io_kiocb *req)
{
}
static bool io_rw_should_reissue(struct io_kiocb *req)
{
        return false;
}
#endif

static void io_req_end_write(struct io_kiocb *req)
{
        if (req->flags & REQ_F_ISREG) {
                struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);

                kiocb_end_write(&rw->kiocb);
        }
}

/*
 * Trigger the notifications after having done some IO, and finish the write
 * accounting, if any.
 */
static void io_req_io_end(struct io_kiocb *req)
{
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);

        if (rw->kiocb.ki_flags & IOCB_WRITE) {
                io_req_end_write(req);
                fsnotify_modify(req->file);
        } else {
                fsnotify_access(req->file);
        }
}

static bool __io_complete_rw_common(struct io_kiocb *req, long res)
{
        if (unlikely(res != req->cqe.res)) {
                if ((res == -EAGAIN || res == -EOPNOTSUPP) &&
                    io_rw_should_reissue(req)) {
                        /*
                         * Reissue will start accounting again, finish the
                         * current cycle.
                         */
                        io_req_io_end(req);
                        req->flags |= REQ_F_REISSUE | REQ_F_BL_NO_RECYCLE;
                        return true;
                }
                req_set_fail(req);
                req->cqe.res = res;
        }
        return false;
}

static inline int io_fixup_rw_res(struct io_kiocb *req, long res)
{
        struct io_async_rw *io = req->async_data;

        /* add previously done IO, if any */
        if (req_has_async_data(req) && io->bytes_done > 0) {
                if (res < 0)
                        res = io->bytes_done;
                else
                        res += io->bytes_done;
        }
        return res;
}

void io_req_rw_complete(struct io_kiocb *req, struct io_tw_state *ts)
{
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
        struct kiocb *kiocb = &rw->kiocb;

        if ((kiocb->ki_flags & IOCB_DIO_CALLER_COMP) && kiocb->dio_complete) {
                long res = kiocb->dio_complete(rw->kiocb.private);

                io_req_set_res(req, io_fixup_rw_res(req, res), 0);
        }

        io_req_io_end(req);

        if (req->flags & (REQ_F_BUFFER_SELECTED|REQ_F_BUFFER_RING))
                req->cqe.flags |= io_put_kbuf(req, 0);

        io_req_rw_cleanup(req, 0);
        io_req_task_complete(req, ts);
}

static void io_complete_rw(struct kiocb *kiocb, long res)
{
        struct io_rw *rw = container_of(kiocb, struct io_rw, kiocb);
        struct io_kiocb *req = cmd_to_io_kiocb(rw);

        if (!kiocb->dio_complete || !(kiocb->ki_flags & IOCB_DIO_CALLER_COMP)) {
                if (__io_complete_rw_common(req, res))
                        return;
                io_req_set_res(req, io_fixup_rw_res(req, res), 0);
        }
        req->io_task_work.func = io_req_rw_complete;
        __io_req_task_work_add(req, IOU_F_TWQ_LAZY_WAKE);
}

static void io_complete_rw_iopoll(struct kiocb *kiocb, long res)
{
        struct io_rw *rw = container_of(kiocb, struct io_rw, kiocb);
        struct io_kiocb *req = cmd_to_io_kiocb(rw);

        if (kiocb->ki_flags & IOCB_WRITE)
                io_req_end_write(req);
        if (unlikely(res != req->cqe.res)) {
                if (res == -EAGAIN && io_rw_should_reissue(req)) {
                        req->flags |= REQ_F_REISSUE | REQ_F_BL_NO_RECYCLE;
                        return;
                }
                req->cqe.res = res;
        }

        /* order with io_iopoll_complete() checking ->iopoll_completed */
        smp_store_release(&req->iopoll_completed, 1);
}

static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
{
        /* IO was queued async, completion will happen later */
        if (ret == -EIOCBQUEUED)
                return;

        /* transform internal restart error codes */
        if (unlikely(ret < 0)) {
                switch (ret) {
                case -ERESTARTSYS:
                case -ERESTARTNOINTR:
                case -ERESTARTNOHAND:
                case -ERESTART_RESTARTBLOCK:
                        /*
                         * We can't just restart the syscall, since previously
                         * submitted sqes may already be in progress. Just fail
                         * this IO with EINTR.
                         */
                        ret = -EINTR;
                        break;
                }
        }

        INDIRECT_CALL_2(kiocb->ki_complete, io_complete_rw_iopoll,
                        io_complete_rw, kiocb, ret);
}

static int kiocb_done(struct io_kiocb *req, ssize_t ret,
                       unsigned int issue_flags)
{
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
        unsigned final_ret = io_fixup_rw_res(req, ret);

        if (ret >= 0 && req->flags & REQ_F_CUR_POS)
                req->file->f_pos = rw->kiocb.ki_pos;
        if (ret >= 0 && (rw->kiocb.ki_complete == io_complete_rw)) {
                if (!__io_complete_rw_common(req, ret)) {
                        /*
                         * Safe to call io_end from here as we're inline
                         * from the submission path.
                         */
                        io_req_io_end(req);
                        io_req_set_res(req, final_ret,
                                       io_put_kbuf(req, issue_flags));
                        io_req_rw_cleanup(req, issue_flags);
                        return IOU_OK;
                }
        } else {
                io_rw_done(&rw->kiocb, ret);
        }

        if (req->flags & REQ_F_REISSUE) {
                req->flags &= ~REQ_F_REISSUE;
                io_resubmit_prep(req);
                return -EAGAIN;
        }
        return IOU_ISSUE_SKIP_COMPLETE;
}

static inline loff_t *io_kiocb_ppos(struct kiocb *kiocb)
{
        return (kiocb->ki_filp->f_mode & FMODE_STREAM) ? NULL : &kiocb->ki_pos;
}

/*
 * For files that don't have ->read_iter() and ->write_iter(), handle them
 * by looping over ->read() or ->write() manually.
 */
static ssize_t loop_rw_iter(int ddir, struct io_rw *rw, struct iov_iter *iter)
{
        struct kiocb *kiocb = &rw->kiocb;
        struct file *file = kiocb->ki_filp;
        ssize_t ret = 0;
        loff_t *ppos;

        /*
         * Don't support polled IO through this interface, and we can't
         * support non-blocking either. For the latter, this just causes
         * the kiocb to be handled from an async context.
         */
        if (kiocb->ki_flags & IOCB_HIPRI)
                return -EOPNOTSUPP;
        if ((kiocb->ki_flags & IOCB_NOWAIT) &&
            !(kiocb->ki_filp->f_flags & O_NONBLOCK))
                return -EAGAIN;

        ppos = io_kiocb_ppos(kiocb);

        while (iov_iter_count(iter)) {
                void __user *addr;
                size_t len;
                ssize_t nr;

                if (iter_is_ubuf(iter)) {
                        addr = iter->ubuf + iter->iov_offset;
                        len = iov_iter_count(iter);
                } else if (!iov_iter_is_bvec(iter)) {
                        addr = iter_iov_addr(iter);
                        len = iter_iov_len(iter);
                } else {
                        addr = u64_to_user_ptr(rw->addr);
                        len = rw->len;
                }

                if (ddir == READ)
                        nr = file->f_op->read(file, addr, len, ppos);
                else
                        nr = file->f_op->write(file, addr, len, ppos);

                if (nr < 0) {
                        if (!ret)
                                ret = nr;
                        break;
                }
                ret += nr;
                if (!iov_iter_is_bvec(iter)) {
                        iov_iter_advance(iter, nr);
                } else {
                        rw->addr += nr;
                        rw->len -= nr;
                        if (!rw->len)
                                break;
                }
                if (nr != len)
                        break;
        }

        return ret;
}

/*
 * This is our waitqueue callback handler, registered through __folio_lock_async()
 * when we initially tried to do the IO with the iocb armed our waitqueue.
 * This gets called when the page is unlocked, and we generally expect that to
 * happen when the page IO is completed and the page is now uptodate. This will
 * queue a task_work based retry of the operation, attempting to copy the data
 * again. If the latter fails because the page was NOT uptodate, then we will
 * do a thread based blocking retry of the operation. That's the unexpected
 * slow path.
 */
static int io_async_buf_func(struct wait_queue_entry *wait, unsigned mode,
                             int sync, void *arg)
{
        struct wait_page_queue *wpq;
        struct io_kiocb *req = wait->private;
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
        struct wait_page_key *key = arg;

        wpq = container_of(wait, struct wait_page_queue, wait);

        if (!wake_page_match(wpq, key))
                return 0;

        rw->kiocb.ki_flags &= ~IOCB_WAITQ;
        list_del_init(&wait->entry);
        io_req_task_queue(req);
        return 1;
}

/*
 * This controls whether a given IO request should be armed for async page
 * based retry. If we return false here, the request is handed to the async
 * worker threads for retry. If we're doing buffered reads on a regular file,
 * we prepare a private wait_page_queue entry and retry the operation. This
 * will either succeed because the page is now uptodate and unlocked, or it
 * will register a callback when the page is unlocked at IO completion. Through
 * that callback, io_uring uses task_work to setup a retry of the operation.
 * That retry will attempt the buffered read again. The retry will generally
 * succeed, or in rare cases where it fails, we then fall back to using the
 * async worker threads for a blocking retry.
 */
static bool io_rw_should_retry(struct io_kiocb *req)
{
        struct io_async_rw *io = req->async_data;
        struct wait_page_queue *wait = &io->wpq;
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
        struct kiocb *kiocb = &rw->kiocb;

        /* never retry for NOWAIT, we just complete with -EAGAIN */
        if (req->flags & REQ_F_NOWAIT)
                return false;

        /* Only for buffered IO */
        if (kiocb->ki_flags & (IOCB_DIRECT | IOCB_HIPRI))
                return false;

        /*
         * just use poll if we can, and don't attempt if the fs doesn't
         * support callback based unlocks
         */
        if (io_file_can_poll(req) ||
            !(req->file->f_op->fop_flags & FOP_BUFFER_RASYNC))
                return false;

        wait->wait.func = io_async_buf_func;
        wait->wait.private = req;
        wait->wait.flags = 0;
        INIT_LIST_HEAD(&wait->wait.entry);
        kiocb->ki_flags |= IOCB_WAITQ;
        kiocb->ki_flags &= ~IOCB_NOWAIT;
        kiocb->ki_waitq = wait;
        return true;
}

static inline int io_iter_do_read(struct io_rw *rw, struct iov_iter *iter)
{
        struct file *file = rw->kiocb.ki_filp;

        if (likely(file->f_op->read_iter))
                return file->f_op->read_iter(&rw->kiocb, iter);
        else if (file->f_op->read)
                return loop_rw_iter(READ, rw, iter);
        else
                return -EINVAL;
}

static bool need_complete_io(struct io_kiocb *req)
{
        return req->flags & REQ_F_ISREG ||
                S_ISBLK(file_inode(req->file)->i_mode);
}

static int io_rw_init_file(struct io_kiocb *req, fmode_t mode)
{
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
        struct kiocb *kiocb = &rw->kiocb;
        struct io_ring_ctx *ctx = req->ctx;
        struct file *file = req->file;
        int ret;

        if (unlikely(!(file->f_mode & mode)))
                return -EBADF;

        if (!(req->flags & REQ_F_FIXED_FILE))
                req->flags |= io_file_get_flags(file);

        kiocb->ki_flags = file->f_iocb_flags;
        ret = kiocb_set_rw_flags(kiocb, rw->flags);
        if (unlikely(ret))
                return ret;
        kiocb->ki_flags |= IOCB_ALLOC_CACHE;

        /*
         * If the file is marked O_NONBLOCK, still allow retry for it if it
         * supports async. Otherwise it's impossible to use O_NONBLOCK files
         * reliably. If not, or it IOCB_NOWAIT is set, don't retry.
         */
        if ((kiocb->ki_flags & IOCB_NOWAIT) ||
            ((file->f_flags & O_NONBLOCK) && !io_file_supports_nowait(req)))
                req->flags |= REQ_F_NOWAIT;

        if (ctx->flags & IORING_SETUP_IOPOLL) {
                if (!(kiocb->ki_flags & IOCB_DIRECT) || !file->f_op->iopoll)
                        return -EOPNOTSUPP;

                kiocb->private = NULL;
                kiocb->ki_flags |= IOCB_HIPRI;
                kiocb->ki_complete = io_complete_rw_iopoll;
                req->iopoll_completed = 0;
        } else {
                if (kiocb->ki_flags & IOCB_HIPRI)
                        return -EINVAL;
                kiocb->ki_complete = io_complete_rw;
        }

        return 0;
}

static int __io_read(struct io_kiocb *req, unsigned int issue_flags)
{
        bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
        struct io_async_rw *io = req->async_data;
        struct kiocb *kiocb = &rw->kiocb;
        ssize_t ret;
        loff_t *ppos;

        if (io_do_buffer_select(req)) {
                ret = io_import_iovec(ITER_DEST, req, io, issue_flags);
                if (unlikely(ret < 0))
                        return ret;
        }

        ret = io_rw_init_file(req, FMODE_READ);
        if (unlikely(ret))
                return ret;
        req->cqe.res = iov_iter_count(&io->iter);

        if (force_nonblock) {
                /* If the file doesn't support async, just async punt */
                if (unlikely(!io_file_supports_nowait(req)))
                        return -EAGAIN;
                kiocb->ki_flags |= IOCB_NOWAIT;
        } else {
                /* Ensure we clear previously set non-block flag */
                kiocb->ki_flags &= ~IOCB_NOWAIT;
        }

        ppos = io_kiocb_update_pos(req);

        ret = rw_verify_area(READ, req->file, ppos, req->cqe.res);
        if (unlikely(ret))
                return ret;

        ret = io_iter_do_read(rw, &io->iter);

        if (ret == -EAGAIN || (req->flags & REQ_F_REISSUE)) {
                req->flags &= ~REQ_F_REISSUE;
                /* If we can poll, just do that. */
                if (io_file_can_poll(req))
                        return -EAGAIN;
                /* IOPOLL retry should happen for io-wq threads */
                if (!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL))
                        goto done;
                /* no retry on NONBLOCK nor RWF_NOWAIT */
                if (req->flags & REQ_F_NOWAIT)
                        goto done;
                ret = 0;
        } else if (ret == -EIOCBQUEUED) {
                return IOU_ISSUE_SKIP_COMPLETE;
        } else if (ret == req->cqe.res || ret <= 0 || !force_nonblock ||
                   (req->flags & REQ_F_NOWAIT) || !need_complete_io(req)) {
                /* read all, failed, already did sync or don't want to retry */
                goto done;
        }

        /*
         * Don't depend on the iter state matching what was consumed, or being
         * untouched in case of error. Restore it and we'll advance it
         * manually if we need to.
         */
        iov_iter_restore(&io->iter, &io->iter_state);

        do {
                /*
                 * We end up here because of a partial read, either from
                 * above or inside this loop. Advance the iter by the bytes
                 * that were consumed.
                 */
                iov_iter_advance(&io->iter, ret);
                if (!iov_iter_count(&io->iter))
                        break;
                io->bytes_done += ret;
                iov_iter_save_state(&io->iter, &io->iter_state);

                /* if we can retry, do so with the callbacks armed */
                if (!io_rw_should_retry(req)) {
                        kiocb->ki_flags &= ~IOCB_WAITQ;
                        return -EAGAIN;
                }

                req->cqe.res = iov_iter_count(&io->iter);
                /*
                 * Now retry read with the IOCB_WAITQ parts set in the iocb. If
                 * we get -EIOCBQUEUED, then we'll get a notification when the
                 * desired page gets unlocked. We can also get a partial read
                 * here, and if we do, then just retry at the new offset.
                 */
                ret = io_iter_do_read(rw, &io->iter);
                if (ret == -EIOCBQUEUED)
                        return IOU_ISSUE_SKIP_COMPLETE;
                /* we got some bytes, but not all. retry. */
                kiocb->ki_flags &= ~IOCB_WAITQ;
                iov_iter_restore(&io->iter, &io->iter_state);
        } while (ret > 0);
done:
        /* it's faster to check here then delegate to kfree */
        return ret;
}

int io_read(struct io_kiocb *req, unsigned int issue_flags)
{
        int ret;

        ret = __io_read(req, issue_flags);
        if (ret >= 0)
                return kiocb_done(req, ret, issue_flags);

        return ret;
}

int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags)
{
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
        unsigned int cflags = 0;
        int ret;

        /*
         * Multishot MUST be used on a pollable file
         */
        if (!io_file_can_poll(req))
                return -EBADFD;

        ret = __io_read(req, issue_flags);

        /*
         * If the file doesn't support proper NOWAIT, then disable multishot
         * and stay in single shot mode.
         */
        if (!io_file_supports_nowait(req))
                req->flags &= ~REQ_F_APOLL_MULTISHOT;

        /*
         * If we get -EAGAIN, recycle our buffer and just let normal poll
         * handling arm it.
         */
        if (ret == -EAGAIN) {
                /*
                 * Reset rw->len to 0 again to avoid clamping future mshot
                 * reads, in case the buffer size varies.
                 */
                if (io_kbuf_recycle(req, issue_flags))
                        rw->len = 0;
                if (issue_flags & IO_URING_F_MULTISHOT)
                        return IOU_ISSUE_SKIP_COMPLETE;
                return -EAGAIN;
        }

        /*
         * Any successful return value will keep the multishot read armed.
         */
        if (ret > 0 && req->flags & REQ_F_APOLL_MULTISHOT) {
                /*
                 * Put our buffer and post a CQE. If we fail to post a CQE, then
                 * jump to the termination path. This request is then done.
                 */
                cflags = io_put_kbuf(req, issue_flags);
                rw->len = 0; /* similarly to above, reset len to 0 */

                if (io_req_post_cqe(req, ret, cflags | IORING_CQE_F_MORE)) {
                        if (issue_flags & IO_URING_F_MULTISHOT) {
                                /*
                                 * Force retry, as we might have more data to
                                 * be read and otherwise it won't get retried
                                 * until (if ever) another poll is triggered.
                                 */
                                io_poll_multishot_retry(req);
                                return IOU_ISSUE_SKIP_COMPLETE;
                        }
                        return -EAGAIN;
                }
        }

        /*
         * Either an error, or we've hit overflow posting the CQE. For any
         * multishot request, hitting overflow will terminate it.
         */
        io_req_set_res(req, ret, cflags);
        io_req_rw_cleanup(req, issue_flags);
        if (issue_flags & IO_URING_F_MULTISHOT)
                return IOU_STOP_MULTISHOT;
        return IOU_OK;
}

int io_write(struct io_kiocb *req, unsigned int issue_flags)
{
        bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
        struct io_async_rw *io = req->async_data;
        struct kiocb *kiocb = &rw->kiocb;
        ssize_t ret, ret2;
        loff_t *ppos;

        ret = io_rw_init_file(req, FMODE_WRITE);
        if (unlikely(ret))
                return ret;
        req->cqe.res = iov_iter_count(&io->iter);

        if (force_nonblock) {
                /* If the file doesn't support async, just async punt */
                if (unlikely(!io_file_supports_nowait(req)))
                        goto ret_eagain;

                /* Check if we can support NOWAIT. */
                if (!(kiocb->ki_flags & IOCB_DIRECT) &&
                    !(req->file->f_op->fop_flags & FOP_BUFFER_WASYNC) &&
                    (req->flags & REQ_F_ISREG))
                        goto ret_eagain;

                kiocb->ki_flags |= IOCB_NOWAIT;
        } else {
                /* Ensure we clear previously set non-block flag */
                kiocb->ki_flags &= ~IOCB_NOWAIT;
        }

        ppos = io_kiocb_update_pos(req);

        ret = rw_verify_area(WRITE, req->file, ppos, req->cqe.res);
        if (unlikely(ret))
                return ret;

        if (req->flags & REQ_F_ISREG)
                kiocb_start_write(kiocb);
        kiocb->ki_flags |= IOCB_WRITE;

        if (likely(req->file->f_op->write_iter))
                ret2 = req->file->f_op->write_iter(kiocb, &io->iter);
        else if (req->file->f_op->write)
                ret2 = loop_rw_iter(WRITE, rw, &io->iter);
        else
                ret2 = -EINVAL;

        if (req->flags & REQ_F_REISSUE) {
                req->flags &= ~REQ_F_REISSUE;
                ret2 = -EAGAIN;
        }

        /*
         * Raw bdev writes will return -EOPNOTSUPP for IOCB_NOWAIT. Just
         * retry them without IOCB_NOWAIT.
         */
        if (ret2 == -EOPNOTSUPP && (kiocb->ki_flags & IOCB_NOWAIT))
                ret2 = -EAGAIN;
        /* no retry on NONBLOCK nor RWF_NOWAIT */
        if (ret2 == -EAGAIN && (req->flags & REQ_F_NOWAIT))
                goto done;
        if (!force_nonblock || ret2 != -EAGAIN) {
                /* IOPOLL retry should happen for io-wq threads */
                if (ret2 == -EAGAIN && (req->ctx->flags & IORING_SETUP_IOPOLL))
                        goto ret_eagain;

                if (ret2 != req->cqe.res && ret2 >= 0 && need_complete_io(req)) {
                        trace_io_uring_short_write(req->ctx, kiocb->ki_pos - ret2,
                                                req->cqe.res, ret2);

                        /* This is a partial write. The file pos has already been
                         * updated, setup the async struct to complete the request
                         * in the worker. Also update bytes_done to account for
                         * the bytes already written.
                         */
                        iov_iter_save_state(&io->iter, &io->iter_state);
                        io->bytes_done += ret2;

                        if (kiocb->ki_flags & IOCB_WRITE)
                                io_req_end_write(req);
                        return -EAGAIN;
                }
done:
                return kiocb_done(req, ret2, issue_flags);
        } else {
ret_eagain:
                iov_iter_restore(&io->iter, &io->iter_state);
                if (kiocb->ki_flags & IOCB_WRITE)
                        io_req_end_write(req);
                return -EAGAIN;
        }
}

void io_rw_fail(struct io_kiocb *req)
{
        int res;

        res = io_fixup_rw_res(req, req->cqe.res);
        io_req_set_res(req, res, req->cqe.flags);
}

int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
{
        struct io_wq_work_node *pos, *start, *prev;
        unsigned int poll_flags = 0;
        DEFINE_IO_COMP_BATCH(iob);
        int nr_events = 0;

        /*
         * Only spin for completions if we don't have multiple devices hanging
         * off our complete list.
         */
        if (ctx->poll_multi_queue || force_nonspin)
                poll_flags |= BLK_POLL_ONESHOT;

        wq_list_for_each(pos, start, &ctx->iopoll_list) {
                struct io_kiocb *req = container_of(pos, struct io_kiocb, comp_list);
                struct file *file = req->file;
                int ret;

                /*
                 * Move completed and retryable entries to our local lists.
                 * If we find a request that requires polling, break out
                 * and complete those lists first, if we have entries there.
                 */
                if (READ_ONCE(req->iopoll_completed))
                        break;

                if (req->opcode == IORING_OP_URING_CMD) {
                        struct io_uring_cmd *ioucmd;

                        ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
                        ret = file->f_op->uring_cmd_iopoll(ioucmd, &iob,
                                                                poll_flags);
                } else {
                        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);

                        ret = file->f_op->iopoll(&rw->kiocb, &iob, poll_flags);
                }
                if (unlikely(ret < 0))
                        return ret;
                else if (ret)
                        poll_flags |= BLK_POLL_ONESHOT;

                /* iopoll may have completed current req */
                if (!rq_list_empty(iob.req_list) ||
                    READ_ONCE(req->iopoll_completed))
                        break;
        }

        if (!rq_list_empty(iob.req_list))
                iob.complete(&iob);
        else if (!pos)
                return 0;

        prev = start;
        wq_list_for_each_resume(pos, prev) {
                struct io_kiocb *req = container_of(pos, struct io_kiocb, comp_list);

                /* order with io_complete_rw_iopoll(), e.g. ->result updates */
                if (!smp_load_acquire(&req->iopoll_completed))
                        break;
                nr_events++;
                req->cqe.flags = io_put_kbuf(req, 0);
                if (req->opcode != IORING_OP_URING_CMD)
                        io_req_rw_cleanup(req, 0);
        }
        if (unlikely(!nr_events))
                return 0;

        pos = start ? start->next : ctx->iopoll_list.first;
        wq_list_cut(&ctx->iopoll_list, prev, start);

        if (WARN_ON_ONCE(!wq_list_empty(&ctx->submit_state.compl_reqs)))
                return 0;
        ctx->submit_state.compl_reqs.first = pos;
        __io_submit_flush_completions(ctx);
        return nr_events;
}

void io_rw_cache_free(const void *entry)
{
        struct io_async_rw *rw = (struct io_async_rw *) entry;

        if (rw->free_iovec) {
                kasan_mempool_unpoison_object(rw->free_iovec,
                                rw->free_iov_nr * sizeof(struct iovec));
                io_rw_iovec_free(rw);
        }
        kfree(rw);
}