io_uring/msg_ring: drop unnecessary submitter_task checks

__io_msg_ring_data() checks that the target_ctx isn't
IORING_SETUP_R_DISABLED before calling io_msg_data_remote(), which calls
io_msg_remote_post(). So submitter_task can't be modified concurrently
with the read in io_msg_remote_post(). Additionally, submitter_task must
exist, as io_msg_data_remote() is only called for io_msg_need_remote(),
i.e. task_complete is set, which requires IORING_SETUP_DEFER_TASKRUN,
which in turn requires IORING_SETUP_SINGLE_ISSUER. And submitter_task is
assigned in io_uring_create() or io_register_enable_rings() before
enabling any IORING_SETUP_SINGLE_ISSUER io_ring_ctx.
Similarly, io_msg_send_fd() checks IORING_SETUP_R_DISABLED and
io_msg_need_remote() before calling io_msg_fd_remote(). submitter_task
therefore can't be modified concurrently with the read in
io_msg_fd_remote() and must be non-null.
io_register_enable_rings() can't run concurrently because it's called
from io_uring_register() -> __io_uring_register() with uring_lock held.
Thus, replace the READ_ONCE() and WRITE_ONCE() of submitter_task with
plain loads and stores. And remove the NULL checks of submitter_task in
io_msg_remote_post() and io_msg_fd_remote().

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 559932b851ca81495e1c353437371b5a553abd25..a1dd1540ab79d45bf34f8de3555eeca4aa01681a 100644 (file)
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3637,13 +3637,8 @@ static __cold int io_uring_create(struct io_ctx_config *config)
        }
 
        if (ctx->flags & IORING_SETUP_SINGLE_ISSUER
-           && !(ctx->flags & IORING_SETUP_R_DISABLED)) {
-               /*
-                * Unlike io_register_enable_rings(), don't need WRITE_ONCE()
-                * since ctx isn't yet accessible from other tasks
-                */
+           && !(ctx->flags & IORING_SETUP_R_DISABLED))
                ctx->submitter_task = get_task_struct(current);
-       }
 
        file = io_uring_get_file(ctx);
        if (IS_ERR(file)) {

diff --git a/io_uring/msg_ring.c b/io_uring/msg_ring.c
index 87b4d306cf1b6ab8d8864644aed595ff26fd7966..57ad0085869a8e8a0532622ad9edb621185d68a9 100644 (file)
--- a/io_uring/msg_ring.c
+++ b/io_uring/msg_ring.c
@@ -80,13 +80,9 @@ static void io_msg_tw_complete(struct io_tw_req tw_req, io_tw_token_t tw)
        percpu_ref_put(&ctx->refs);
 }
 
-static int io_msg_remote_post(struct io_ring_ctx *ctx, struct io_kiocb *req,
+static void io_msg_remote_post(struct io_ring_ctx *ctx, struct io_kiocb *req,
                              int res, u32 cflags, u64 user_data)
 {
-       if (!READ_ONCE(ctx->submitter_task)) {
-               kfree_rcu(req, rcu_head);
-               return -EOWNERDEAD;
-       }
        req->opcode = IORING_OP_NOP;
        req->cqe.user_data = user_data;
        io_req_set_res(req, res, cflags);
@@ -95,7 +91,6 @@ static int io_msg_remote_post(struct io_ring_ctx *ctx, struct io_kiocb *req,
        req->tctx = NULL;
        req->io_task_work.func = io_msg_tw_complete;
        io_req_task_work_add_remote(req, IOU_F_TWQ_LAZY_WAKE);
-       return 0;
 }
 
 static int io_msg_data_remote(struct io_ring_ctx *target_ctx,
@@ -111,8 +106,8 @@ static int io_msg_data_remote(struct io_ring_ctx *target_ctx,
        if (msg->flags & IORING_MSG_RING_FLAGS_PASS)
                flags = msg->cqe_flags;
 
-       return io_msg_remote_post(target_ctx, target, msg->len, flags,
-                                       msg->user_data);
+       io_msg_remote_post(target_ctx, target, msg->len, flags, msg->user_data);
+       return 0;
 }
 
 static int __io_msg_ring_data(struct io_ring_ctx *target_ctx,
@@ -127,7 +122,7 @@ static int __io_msg_ring_data(struct io_ring_ctx *target_ctx,
                return -EINVAL;
        /*
         * Keep IORING_SETUP_R_DISABLED check before submitter_task load
-        * in io_msg_data_remote() -> io_msg_remote_post()
+        * in io_msg_data_remote() -> io_req_task_work_add_remote()
         */
        if (smp_load_acquire(&target_ctx->flags) & IORING_SETUP_R_DISABLED)
                return -EBADFD;
@@ -227,10 +222,7 @@ static int io_msg_fd_remote(struct io_kiocb *req)
 {
        struct io_ring_ctx *ctx = req->file->private_data;
        struct io_msg *msg = io_kiocb_to_cmd(req, struct io_msg);
-       struct task_struct *task = READ_ONCE(ctx->submitter_task);
-
-       if (unlikely(!task))
-               return -EOWNERDEAD;
+       struct task_struct *task = ctx->submitter_task;
 
        init_task_work(&msg->tw, io_msg_tw_fd_complete);
        if (task_work_add(task, &msg->tw, TWA_SIGNAL))

diff --git a/io_uring/register.c b/io_uring/register.c
index 5c2574496aa991c1f48069e08bf8bd6a26ec4253..29393f93a4143b070a00fb146424cd08130d4de6 100644 (file)
--- a/io_uring/register.c
+++ b/io_uring/register.c
@@ -181,7 +181,7 @@ static int io_register_enable_rings(struct io_ring_ctx *ctx)
                return -EBADFD;
 
        if (ctx->flags & IORING_SETUP_SINGLE_ISSUER && !ctx->submitter_task) {
-               WRITE_ONCE(ctx->submitter_task, get_task_struct(current));
+               ctx->submitter_task = get_task_struct(current);
                /*
                 * Lazy activation attempts would fail if it was polled before
                 * submitter_task is set.