io_uring: replace list with array for compl batch

Reincarnation of an old patch that replaces a list in struct
io_compl_batch with an array. It's needed to avoid hooking requests via
their compl.list, because it won't be always available in the future.

It's also nice to split io_submit_flush_completions() to avoid free
under locks and remove unlock/lock with a long comment describing when
it can be done.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6bce9094280cd78610f9b97cc66f530abcf6353f..aef640616edb916c4869a51756e31826cccde6a6 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -265,10 +265,11 @@ struct io_sq_data {
 };
 
 #define IO_IOPOLL_BATCH                        8
+#define IO_COMPL_BATCH                 32
 
 struct io_comp_state {
        unsigned int            nr;
-       struct list_head        list;
+       struct io_kiocb         *reqs[IO_COMPL_BATCH];
 };
 
 struct io_submit_state {
@@ -1345,7 +1346,6 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
        INIT_LIST_HEAD(&ctx->rsrc_ref_list);
        INIT_DELAYED_WORK(&ctx->rsrc_put_work, io_rsrc_put_work);
        init_llist_head(&ctx->rsrc_put_llist);
-       INIT_LIST_HEAD(&submit_state->comp.list);
        return ctx;
 err:
        if (ctx->fallback_req)
@@ -1927,33 +1927,20 @@ static inline void io_req_complete_nostate(struct io_kiocb *req, long res,
 static void io_submit_flush_completions(struct io_comp_state *cs,
                                        struct io_ring_ctx *ctx)
 {
+       int i, nr = cs->nr;
+
        spin_lock_irq(&ctx->completion_lock);
-       while (!list_empty(&cs->list)) {
-               struct io_kiocb *req;
+       for (i = 0; i < nr; i++) {
+               struct io_kiocb *req = cs->reqs[i];
 
-               req = list_first_entry(&cs->list, struct io_kiocb, compl.list);
-               list_del(&req->compl.list);
                __io_cqring_fill_event(req, req->result, req->compl.cflags);
-
-               /*
-                * io_free_req() doesn't care about completion_lock unless one
-                * of these flags is set. REQ_F_WORK_INITIALIZED is in the list
-                * because of a potential deadlock with req->work.fs->lock
-                * We defer both, completion and submission refs.
-                */
-               if (req->flags & (REQ_F_FAIL_LINK|REQ_F_LINK_TIMEOUT
-                                |REQ_F_WORK_INITIALIZED)) {
-                       spin_unlock_irq(&ctx->completion_lock);
-                       io_double_put_req(req);
-                       spin_lock_irq(&ctx->completion_lock);
-               } else {
-                       io_double_put_req(req);
-               }
        }
        io_commit_cqring(ctx);
        spin_unlock_irq(&ctx->completion_lock);
 
        io_cqring_ev_posted(ctx);
+       for (i = 0; i < nr; i++)
+               io_double_put_req(cs->reqs[i]);
        cs->nr = 0;
 }
 
@@ -6517,8 +6504,8 @@ again:
        } else if (likely(!ret)) {
                /* drop submission reference */
                if (req->flags & REQ_F_COMPLETE_INLINE) {
-                       list_add_tail(&req->compl.list, &cs->list);
-                       if (++cs->nr >= 32)
+                       cs->reqs[cs->nr++] = req;
+                       if (cs->nr == IO_COMPL_BATCH)
                                io_submit_flush_completions(cs, req->ctx);
                        req = NULL;
                } else {
@@ -6657,7 +6644,7 @@ static int io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 static void io_submit_state_end(struct io_submit_state *state,
                                struct io_ring_ctx *ctx)
 {
-       if (!list_empty(&state->comp.list))
+       if (state->comp.nr)
                io_submit_flush_completions(&state->comp, ctx);
        if (state->plug_started)
                blk_finish_plug(&state->plug);