io_uring: support for IO polling
Add support for a polled io_uring instance. When a read or write is submitted to a polled io_uring, the application must poll for completions on the CQ ring through io_uring_enter(2). Polled IO may not generate IRQ completions, hence they need to be actively found by the application itself. To use polling, io_uring_setup() must be used with the IORING_SETUP_IOPOLL flag being set. It is illegal to mix and match polled and non-polled IO on an io_uring. Reviewed-by: Hannes Reinecke <hare@suse.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe
parent
c992fe2925
commit
def596e955
261
fs/io_uring.c
261
fs/io_uring.c
@ -124,6 +124,14 @@ struct io_ring_ctx {
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struct {
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spinlock_t completion_lock;
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bool poll_multi_file;
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/*
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* ->poll_list is protected by the ctx->uring_lock for
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* io_uring instances that don't use IORING_SETUP_SQPOLL.
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* For SQPOLL, only the single threaded io_sq_thread() will
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* manipulate the list, hence no extra locking is needed there.
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*/
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struct list_head poll_list;
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} ____cacheline_aligned_in_smp;
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#if defined(CONFIG_UNIX)
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@ -135,6 +143,7 @@ struct sqe_submit {
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const struct io_uring_sqe *sqe;
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unsigned short index;
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bool has_user;
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bool needs_lock;
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};
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struct io_kiocb {
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@ -146,12 +155,15 @@ struct io_kiocb {
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struct list_head list;
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unsigned int flags;
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#define REQ_F_FORCE_NONBLOCK 1 /* inline submission attempt */
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#define REQ_F_IOPOLL_COMPLETED 2 /* polled IO has completed */
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u64 user_data;
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u64 error;
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struct work_struct work;
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};
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#define IO_PLUG_THRESHOLD 2
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#define IO_IOPOLL_BATCH 8
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static struct kmem_cache *req_cachep;
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@ -196,6 +208,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
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mutex_init(&ctx->uring_lock);
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init_waitqueue_head(&ctx->wait);
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spin_lock_init(&ctx->completion_lock);
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INIT_LIST_HEAD(&ctx->poll_list);
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return ctx;
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}
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@ -297,12 +310,153 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx)
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return NULL;
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}
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static void io_free_req_many(struct io_ring_ctx *ctx, void **reqs, int *nr)
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{
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if (*nr) {
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kmem_cache_free_bulk(req_cachep, *nr, reqs);
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io_ring_drop_ctx_refs(ctx, *nr);
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*nr = 0;
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}
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}
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static void io_free_req(struct io_kiocb *req)
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{
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io_ring_drop_ctx_refs(req->ctx, 1);
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kmem_cache_free(req_cachep, req);
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}
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/*
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* Find and free completed poll iocbs
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*/
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static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
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struct list_head *done)
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{
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void *reqs[IO_IOPOLL_BATCH];
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struct io_kiocb *req;
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int to_free = 0;
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while (!list_empty(done)) {
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req = list_first_entry(done, struct io_kiocb, list);
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list_del(&req->list);
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io_cqring_fill_event(ctx, req->user_data, req->error, 0);
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reqs[to_free++] = req;
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(*nr_events)++;
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fput(req->rw.ki_filp);
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if (to_free == ARRAY_SIZE(reqs))
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io_free_req_many(ctx, reqs, &to_free);
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}
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io_commit_cqring(ctx);
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io_free_req_many(ctx, reqs, &to_free);
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}
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static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
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long min)
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{
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struct io_kiocb *req, *tmp;
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LIST_HEAD(done);
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bool spin;
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int ret;
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/*
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* Only spin for completions if we don't have multiple devices hanging
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* off our complete list, and we're under the requested amount.
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*/
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spin = !ctx->poll_multi_file && *nr_events < min;
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ret = 0;
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list_for_each_entry_safe(req, tmp, &ctx->poll_list, list) {
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struct kiocb *kiocb = &req->rw;
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/*
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* Move completed entries to our local list. If we find a
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* request that requires polling, break out and complete
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* the done list first, if we have entries there.
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*/
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if (req->flags & REQ_F_IOPOLL_COMPLETED) {
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list_move_tail(&req->list, &done);
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continue;
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}
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if (!list_empty(&done))
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break;
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ret = kiocb->ki_filp->f_op->iopoll(kiocb, spin);
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if (ret < 0)
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break;
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if (ret && spin)
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spin = false;
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ret = 0;
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}
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if (!list_empty(&done))
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io_iopoll_complete(ctx, nr_events, &done);
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return ret;
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}
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/*
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* Poll for a mininum of 'min' events. Note that if min == 0 we consider that a
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* non-spinning poll check - we'll still enter the driver poll loop, but only
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* as a non-spinning completion check.
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*/
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static int io_iopoll_getevents(struct io_ring_ctx *ctx, unsigned int *nr_events,
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long min)
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{
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while (!list_empty(&ctx->poll_list)) {
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int ret;
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ret = io_do_iopoll(ctx, nr_events, min);
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if (ret < 0)
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return ret;
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if (!min || *nr_events >= min)
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return 0;
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}
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return 1;
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}
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/*
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* We can't just wait for polled events to come to us, we have to actively
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* find and complete them.
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*/
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static void io_iopoll_reap_events(struct io_ring_ctx *ctx)
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{
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if (!(ctx->flags & IORING_SETUP_IOPOLL))
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return;
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mutex_lock(&ctx->uring_lock);
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while (!list_empty(&ctx->poll_list)) {
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unsigned int nr_events = 0;
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io_iopoll_getevents(ctx, &nr_events, 1);
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}
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mutex_unlock(&ctx->uring_lock);
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}
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static int io_iopoll_check(struct io_ring_ctx *ctx, unsigned *nr_events,
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long min)
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{
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int ret = 0;
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do {
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int tmin = 0;
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if (*nr_events < min)
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tmin = min - *nr_events;
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ret = io_iopoll_getevents(ctx, nr_events, tmin);
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if (ret <= 0)
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break;
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ret = 0;
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} while (min && !*nr_events && !need_resched());
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return ret;
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}
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static void kiocb_end_write(struct kiocb *kiocb)
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{
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if (kiocb->ki_flags & IOCB_WRITE) {
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@ -329,6 +483,53 @@ static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
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io_free_req(req);
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}
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static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
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{
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struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
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kiocb_end_write(kiocb);
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req->error = res;
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if (res != -EAGAIN)
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req->flags |= REQ_F_IOPOLL_COMPLETED;
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}
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/*
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* After the iocb has been issued, it's safe to be found on the poll list.
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* Adding the kiocb to the list AFTER submission ensures that we don't
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* find it from a io_iopoll_getevents() thread before the issuer is done
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* accessing the kiocb cookie.
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*/
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static void io_iopoll_req_issued(struct io_kiocb *req)
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{
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struct io_ring_ctx *ctx = req->ctx;
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/*
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* Track whether we have multiple files in our lists. This will impact
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* how we do polling eventually, not spinning if we're on potentially
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* different devices.
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*/
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if (list_empty(&ctx->poll_list)) {
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ctx->poll_multi_file = false;
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} else if (!ctx->poll_multi_file) {
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struct io_kiocb *list_req;
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list_req = list_first_entry(&ctx->poll_list, struct io_kiocb,
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list);
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if (list_req->rw.ki_filp != req->rw.ki_filp)
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ctx->poll_multi_file = true;
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}
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/*
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* For fast devices, IO may have already completed. If it has, add
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* it to the front so we find it first.
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*/
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if (req->flags & REQ_F_IOPOLL_COMPLETED)
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list_add(&req->list, &ctx->poll_list);
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else
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list_add_tail(&req->list, &ctx->poll_list);
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}
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/*
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* If we tracked the file through the SCM inflight mechanism, we could support
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* any file. For now, just ensure that anything potentially problematic is done
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@ -349,6 +550,7 @@ static bool io_file_supports_async(struct file *file)
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static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
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bool force_nonblock)
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{
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struct io_ring_ctx *ctx = req->ctx;
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struct kiocb *kiocb = &req->rw;
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unsigned ioprio;
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int fd, ret;
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@ -384,12 +586,22 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
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kiocb->ki_flags |= IOCB_NOWAIT;
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req->flags |= REQ_F_FORCE_NONBLOCK;
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}
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if (ctx->flags & IORING_SETUP_IOPOLL) {
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ret = -EOPNOTSUPP;
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if (!(kiocb->ki_flags & IOCB_DIRECT) ||
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!kiocb->ki_filp->f_op->iopoll)
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goto out_fput;
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req->error = 0;
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kiocb->ki_flags |= IOCB_HIPRI;
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kiocb->ki_complete = io_complete_rw_iopoll;
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} else {
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if (kiocb->ki_flags & IOCB_HIPRI) {
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ret = -EINVAL;
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goto out_fput;
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}
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kiocb->ki_complete = io_complete_rw;
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}
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return 0;
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out_fput:
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fput(kiocb->ki_filp);
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@ -543,6 +755,9 @@ static int io_nop(struct io_kiocb *req, u64 user_data)
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struct io_ring_ctx *ctx = req->ctx;
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long err = 0;
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if (unlikely(ctx->flags & IORING_SETUP_IOPOLL))
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return -EINVAL;
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/*
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* Twilight zone - it's possible that someone issued an opcode that
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* has a file attached, then got -EAGAIN on submission, and changed
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@ -566,6 +781,8 @@ static int io_prep_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe)
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if (req->rw.ki_filp)
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return 0;
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if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
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return -EINVAL;
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if (unlikely(sqe->addr || sqe->ioprio))
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return -EINVAL;
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@ -637,7 +854,22 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
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break;
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}
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if (ret)
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return ret;
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if (ctx->flags & IORING_SETUP_IOPOLL) {
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if (req->error == -EAGAIN)
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return -EAGAIN;
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/* workqueue context doesn't hold uring_lock, grab it now */
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if (s->needs_lock)
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mutex_lock(&ctx->uring_lock);
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io_iopoll_req_issued(req);
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if (s->needs_lock)
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mutex_unlock(&ctx->uring_lock);
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}
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return 0;
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}
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static void io_sq_wq_submit_work(struct work_struct *work)
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@ -661,8 +893,19 @@ static void io_sq_wq_submit_work(struct work_struct *work)
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use_mm(ctx->sqo_mm);
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set_fs(USER_DS);
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s->has_user = true;
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s->needs_lock = true;
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do {
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ret = __io_submit_sqe(ctx, req, s, false);
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/*
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* We can get EAGAIN for polled IO even though we're forcing
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* a sync submission from here, since we can't wait for
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* request slots on the block side.
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*/
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if (ret != -EAGAIN)
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break;
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cond_resched();
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} while (1);
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set_fs(old_fs);
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unuse_mm(ctx->sqo_mm);
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@ -799,6 +1042,8 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
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break;
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s.has_user = true;
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s.needs_lock = false;
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ret = io_submit_sqe(ctx, &s);
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if (ret) {
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io_drop_sqring(ctx);
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@ -947,6 +1192,9 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
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destroy_workqueue(ctx->sqo_wq);
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if (ctx->sqo_mm)
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mmdrop(ctx->sqo_mm);
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io_iopoll_reap_events(ctx);
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#if defined(CONFIG_UNIX)
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if (ctx->ring_sock)
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sock_release(ctx->ring_sock);
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@ -993,6 +1241,7 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
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percpu_ref_kill(&ctx->refs);
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mutex_unlock(&ctx->uring_lock);
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io_iopoll_reap_events(ctx);
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wait_for_completion(&ctx->ctx_done);
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io_ring_ctx_free(ctx);
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}
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@ -1074,6 +1323,8 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
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goto out_ctx;
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}
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if (flags & IORING_ENTER_GETEVENTS) {
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unsigned nr_events = 0;
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min_complete = min(min_complete, ctx->cq_entries);
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/*
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@ -1085,8 +1336,14 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
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if (submitted < to_submit)
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min_complete = min_t(unsigned, submitted, min_complete);
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if (ctx->flags & IORING_SETUP_IOPOLL) {
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mutex_lock(&ctx->uring_lock);
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ret = io_iopoll_check(ctx, &nr_events, min_complete);
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mutex_unlock(&ctx->uring_lock);
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} else {
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ret = io_cqring_wait(ctx, min_complete, sig, sigsz);
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}
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}
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out_ctx:
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io_ring_drop_ctx_refs(ctx, 1);
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@ -1282,7 +1539,7 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
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return -EINVAL;
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}
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if (p.flags)
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if (p.flags & ~IORING_SETUP_IOPOLL)
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return -EINVAL;
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ret = io_uring_create(entries, &p);
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@ -30,6 +30,11 @@ struct io_uring_sqe {
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__u64 __pad2[3];
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};
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/*
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* io_uring_setup() flags
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*/
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#define IORING_SETUP_IOPOLL (1U << 0) /* io_context is polled */
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#define IORING_OP_NOP 0
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#define IORING_OP_READV 1
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#define IORING_OP_WRITEV 2
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