[PATCH V2 0/2] ublk: run auto buf unregister on same io_ring_ctx with register

[PATCH V2 0/2] ublk: run auto buf unregister on same io_ring_ctx with register

[Ming Lei]

Hello Jens,

The 1st patch adds helper io_uring_cmd_ctx_handle().

The 2nd one use the added helper to run auto-buf-unreg on the same
io_uring_ctx with the register one.

Thanks,
Ming

V2:
	- return `void *` from io_uring_cmd_ctx_handle() (Caleb Sander Mateos)
	- typo & document fix (Caleb Sander Mateos)


Ming Lei (2):
  io_uring: add helper io_uring_cmd_ctx_handle()
  ublk: run auto buf unregisgering in same io_ring_ctx with registering

 drivers/block/ublk_drv.c      | 19 ++++++++++++++++---
 include/linux/io_uring/cmd.h  |  9 +++++++++
 include/uapi/linux/ublk_cmd.h |  6 +++++-
 3 files changed, 30 insertions(+), 4 deletions(-)

-- 
2.47.0

[PATCH V2 1/2] io_uring: add helper io_uring_cmd_ctx_handle()

[Ming Lei]

Add helper io_uring_cmd_ctx_handle() for driver to track per-context
resource, such as registered kernel io buffer.

Suggested-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/linux/io_uring/cmd.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index 0634a3de1782..53408124c1e5 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -140,6 +140,15 @@ static inline struct io_uring_cmd_data *io_uring_cmd_get_async_data(struct io_ur
 	return cmd_to_io_kiocb(cmd)->async_data;
 }
 
+/*
+ * Return uring_cmd's context reference as its context handle for driver to
+ * track per-context resource, such as registered kernel IO buffer
+ */
+static inline void *io_uring_cmd_ctx_handle(struct io_uring_cmd *cmd)
+{
+	return cmd_to_io_kiocb(cmd)->ctx;
+}
+
 int io_buffer_register_bvec(struct io_uring_cmd *cmd, struct request *rq,
 			    void (*release)(void *), unsigned int index,
 			    unsigned int issue_flags);
-- 
2.47.0

[PATCH V2 2/2] ublk: run auto buf unregisgering in same io_ring_ctx with registering

[Ming Lei]

UBLK_F_AUTO_BUF_REG requires that the buffer registered automatically
is unregistered in same `io_ring_ctx`, so check it explicitly.

Document this requirement for UBLK_F_AUTO_BUF_REG.

Drop WARN_ON_ONCE() which is triggered from userspace code path.

Fixes: 99c1e4eb6a3f ("ublk: register buffer to local io_uring with provided buf index via UBLK_F_AUTO_BUF_REG")
Reported-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/block/ublk_drv.c      | 19 ++++++++++++++++---
 include/uapi/linux/ublk_cmd.h |  6 +++++-
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index fcf568b89370..f44ac5526edd 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -84,6 +84,7 @@ struct ublk_rq_data {
 
 	/* for auto-unregister buffer in case of UBLK_F_AUTO_BUF_REG */
 	u16 buf_index;
+	void *buf_ctx_handle;
 };
 
 struct ublk_uring_cmd_pdu {
@@ -1211,6 +1212,8 @@ static bool ublk_auto_buf_reg(struct request *req, struct ublk_io *io,
 	}
 	/* one extra reference is dropped by ublk_io_release */
 	refcount_set(&data->ref, 2);
+
+	data->buf_ctx_handle = io_uring_cmd_ctx_handle(io->cmd);
 	/* store buffer index in request payload */
 	data->buf_index = pdu->buf.index;
 	io->flags |= UBLK_IO_FLAG_AUTO_BUF_REG;
@@ -2111,12 +2114,22 @@ static int ublk_commit_and_fetch(const struct ublk_queue *ubq,
 	if (ublk_support_auto_buf_reg(ubq)) {
 		int ret;
 
+		/*
+		 * `UBLK_F_AUTO_BUF_REG` only works iff `UBLK_IO_FETCH_REQ`
+		 * and `UBLK_IO_COMMIT_AND_FETCH_REQ` are issued from same
+		 * `io_ring_ctx`.
+		 *
+		 * If this uring_cmd's io_ring_ctx isn't same with the
+		 * one for registering the buffer, it is ublk server's
+		 * responsibility for unregistering the buffer, otherwise
+		 * this ublk request gets stuck.
+		 */
 		if (io->flags & UBLK_IO_FLAG_AUTO_BUF_REG) {
 			struct ublk_rq_data *data = blk_mq_rq_to_pdu(req);
 
-			WARN_ON_ONCE(io_buffer_unregister_bvec(cmd,
-						data->buf_index,
-						issue_flags));
+			if (data->buf_ctx_handle == io_uring_cmd_ctx_handle(cmd))
+				io_buffer_unregister_bvec(cmd, data->buf_index,
+						issue_flags);
 			io->flags &= ~UBLK_IO_FLAG_AUTO_BUF_REG;
 		}
 
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index c4b9942697fc..1c40632cb164 100644
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -226,7 +226,11 @@
  *
  * For using this feature:
  *
- * - ublk server has to create sparse buffer table
+ * - ublk server has to create sparse buffer table on the same `io_ring_ctx`
+ *   for issuing `UBLK_IO_FETCH_REQ` and `UBLK_IO_COMMIT_AND_FETCH_REQ`.
+ *   If uring_cmd isn't issued on same `io_ring_ctx`, it is ublk server's
+ *   responsibility to unregister the buffer by issuing `IO_UNREGISTER_IO_BUF`
+ *   manually, otherwise this ublk request won't complete.
  *
  * - ublk server passes auto buf register data via uring_cmd's sqe->addr,
  *   `struct ublk_auto_buf_reg` is populated from sqe->addr, please see
-- 
2.47.0

Re: [PATCH V2 1/2] io_uring: add helper io_uring_cmd_ctx_handle()

[Caleb Sander Mateos]

On Thu, May 22, 2025 at 8:20 AM Ming Lei <ming.lei@redhat.com> wrote:
>
> Add helper io_uring_cmd_ctx_handle() for driver to track per-context
> resource, such as registered kernel io buffer.
>
> Suggested-by: Caleb Sander Mateos <csander@purestorage.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>

Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>

Re: [PATCH V2 0/2] ublk: run auto buf unregister on same io_ring_ctx with register

[Jens Axboe]

On Thu, 22 May 2025 23:20:38 +0800, Ming Lei wrote:
> The 1st patch adds helper io_uring_cmd_ctx_handle().
> 
> The 2nd one use the added helper to run auto-buf-unreg on the same
> io_uring_ctx with the register one.
> 
> Thanks,
> Ming
> 
> [...]

Applied, thanks!

[1/2] io_uring: add helper io_uring_cmd_ctx_handle()
      commit: 3a91f28fab43f093c72312148288d125ae160c2d
[2/2] ublk: run auto buf unregisgering in same io_ring_ctx with registering
      commit: 914e0dc5082a335ea5e7d905e99e1a1cde001369

Best regards,
-- 
Jens Axboe