[PATCH 1/4] io_uring/uring_cmd: get rid of using req->imu

[Jens Axboe <axboe@kernel.dk>]

It's pretty pointless to use io_kiocb as intermediate storage for this,
so split the validity check and the actual usage. The resource node is
assigned upfront at prep time, to prevent it from going away. The actual
import is never called with the ctx->uring_lock held, so grab it for
the import.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/uring_cmd.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 39c3c816ec78..313e2a389174 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -211,11 +211,15 @@ int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		struct io_ring_ctx *ctx = req->ctx;
 		u16 index;
 
-		req->buf_index = READ_ONCE(sqe->buf_index);
-		if (unlikely(req->buf_index >= ctx->nr_user_bufs))
+		index = READ_ONCE(sqe->buf_index);
+		if (unlikely(index >= ctx->nr_user_bufs))
 			return -EFAULT;
-		index = array_index_nospec(req->buf_index, ctx->nr_user_bufs);
-		req->imu = ctx->user_bufs[index];
+		req->buf_index = array_index_nospec(index, ctx->nr_user_bufs);
+		/*
+		 * Pi node upfront, prior to io_uring_cmd_import_fixed()
+		 * being called. This prevents destruction of the mapped buffer
+		 * we'll need at actual import time.
+		 */
 		io_req_set_rsrc_node(req, ctx, 0);
 	}
 	ioucmd->cmd_op = READ_ONCE(sqe->cmd_op);
@@ -272,8 +276,16 @@ int io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw,
 			      struct iov_iter *iter, void *ioucmd)
 {
 	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_mapped_ubuf *imu;
+	int ret;
 
-	return io_import_fixed(rw, iter, req->imu, ubuf, len);
+	mutex_lock(&ctx->uring_lock);
+	imu = ctx->user_bufs[req->buf_index];
+	ret = io_import_fixed(rw, iter, imu, ubuf, len);
+	mutex_unlock(&ctx->uring_lock);
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(io_uring_cmd_import_fixed);
 
-- 
2.45.2