[RFC v2 3/4] io_uring: introduce IORING_URING_CMD_UNLOCK flag

[Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>]

task_work_cb and its child functions may call io_uring_submit_sqe()
in io_uring_cmd's callback, so to avoid ctx->uring_lock deadlock,
introduce IORING_URING_CMD_UNLOCK to unlock uring_lock temporarily
in io_uring_cmd_work().

Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
---
 include/uapi/linux/io_uring.h | 5 +++++
 io_uring/uring_cmd.c          | 6 +++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 2780bce62faf..45ea8c35d251 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -232,8 +232,13 @@ enum io_uring_op {
  * sqe->uring_cmd_flags
  * IORING_URING_CMD_FIXED	use registered buffer; pass this flag
  *				along with setting sqe->buf_index.
+ *
+ * IORING_URING_CMD_UNLOCK	Notify io_uring_cmd's task_work_cb to
+ *				unlock uring_lock, some ->uring_cmd()
+ *				implementations need it.
  */
 #define IORING_URING_CMD_FIXED	(1U << 0)
+#define IORING_URING_CMD_UNLOCK	(1U << 1)
 
 
 /*
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 446a189b78b0..11488a702832 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -16,7 +16,11 @@ static void io_uring_cmd_work(struct io_kiocb *req, bool *locked)
 {
 	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
 
+	if ((req->flags & IORING_URING_CMD_UNLOCK) && *locked)
+		mutex_unlock(&(req->ctx->uring_lock));
 	ioucmd->task_work_cb(ioucmd);
+	if ((req->flags & IORING_URING_CMD_UNLOCK) && *locked)
+		mutex_lock(&(req->ctx->uring_lock));
 }
 
 void io_uring_cmd_complete_in_task(struct io_uring_cmd *ioucmd,
@@ -82,7 +86,7 @@ int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		return -EINVAL;
 
 	ioucmd->flags = READ_ONCE(sqe->uring_cmd_flags);
-	if (ioucmd->flags & ~IORING_URING_CMD_FIXED)
+	if (ioucmd->flags & ~(IORING_URING_CMD_FIXED | IORING_URING_CMD_UNLOCK))
 		return -EINVAL;
 
 	if (ioucmd->flags & IORING_URING_CMD_FIXED) {
-- 
2.31.1