io_uring: move struct io_kiocb from task_struct to io_uring_task

Rather than store the task_struct itself in struct io_kiocb, store
the io_uring specific task_struct. The life times are the same in terms
of io_uring, and this avoids doing some dereferences through the
task_struct. For the hot path of putting local task references, we can
deref req->tctx instead, which we'll need anyway in that function
regardless of whether it's local or remote references.

This is mostly straight forward, except the original task PF_EXITING
check needs a bit of tweaking. task_work is _always_ run from the
originating task, except in the fallback case, where it's run from a
kernel thread. Replace the potentially racy (in case of fallback work)
checks for req->task->flags with current->flags. It's either the still
the original task, in which case PF_EXITING will be sane, or it has
PF_KTHREAD set, in which case it's fallback work. Both cases should
prevent moving forward with the given request.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 2 insertions, 2 deletions

diff --git a/io_uring/msg_ring.c b/io_uring/msg_ring.c
index 99af39e1d0fb..e63af34004b7 100644
--- a/io_uring/msg_ring.c
+++ b/io_uring/msg_ring.c
@@ -89,8 +89,8 @@ static void io_msg_tw_complete(struct io_kiocb *req, struct io_tw_state *ts)
 static int io_msg_remote_post(struct io_ring_ctx *ctx, struct io_kiocb *req,
 			      int res, u32 cflags, u64 user_data)
 {
-	req->task = READ_ONCE(ctx->submitter_task);
-	if (!req->task) {
+	req->tctx = READ_ONCE(ctx->submitter_task->io_uring);
+	if (!req->tctx) {
 		kmem_cache_free(req_cachep, req);
 		return -EOWNERDEAD;
 	}