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io_uring/msg_ring: drop unnecessary submitter_task checks

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__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>
This commit is contained in:
Caleb Sander Mateos 2026-01-05 14:05:41 -07:00 • committed by Jens Axboe
parent 7a8737e113
commit bcd4c95737
3 changed files with 7 additions and 20 deletions
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7
io_uring/io_uring.c
View file

@ -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)) {

18
io_uring/msg_ring.c
View file

@ -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))

2
io_uring/register.c
View file

@ -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.