Merge branch 'block-6.16' into for-next

* block-6.16:
  selftests: ublk: cover PER_IO_DAEMON in more stress tests
  Documentation: ublk: document UBLK_F_PER_IO_DAEMON
  selftests: ublk: add stress test for per io daemons
  selftests: ublk: add functional test for per io daemons
  selftests: ublk: kublk: decouple ublk_queues from ublk server threads
  selftests: ublk: kublk: move per-thread data out of ublk_queue
  selftests: ublk: kublk: lift queue initialization out of thread
  selftests: ublk: kublk: tie sqe allocation to io instead of queue
  selftests: ublk: kublk: plumb q_id in io_uring user_data
  ublk: have a per-io daemon instead of a per-queue daemon
  md/md-bitmap: remove parameter slot from bitmap_create()
  md/md-bitmap: cleanup bitmap_ops->startwrite()
  md/dm-raid: remove max_write_behind setting limit
  md/md-bitmap: fix dm-raid max_write_behind setting
  md/raid1,raid10: don't handle IO error for REQ_RAHEAD and REQ_NOWAIT
  loop: add file_start_write() and file_end_write()
  bcache: reserve more RESERVE_BTREE buckets to prevent allocator hang
  bcache: remove unused constants
  bcache: fix NULL pointer in cache_set_flush()

Author: axboe

Documentation/block/ublk.rst

@@ -115,15 +115,15 @@ managing and controlling ublk devices with help of several control commands:
 
 - ``UBLK_CMD_START_DEV``
 
-  After the server prepares userspace resources (such as creating per-queue
-  pthread & io_uring for handling ublk IO), this command is sent to the
+  After the server prepares userspace resources (such as creating I/O handler
+  threads & io_uring for handling ublk IO), this command is sent to the
   driver for allocating & exposing ``/dev/ublkb*``. Parameters set via
   ``UBLK_CMD_SET_PARAMS`` are applied for creating the device.
 
 - ``UBLK_CMD_STOP_DEV``
 
   Halt IO on ``/dev/ublkb*`` and remove the device. When this command returns,
-  ublk server will release resources (such as destroying per-queue pthread &
+  ublk server will release resources (such as destroying I/O handler threads &
   io_uring).
 
 - ``UBLK_CMD_DEL_DEV``
@@ -208,15 +208,15 @@ managing and controlling ublk devices with help of several control commands:
   modify how I/O is handled while the ublk server is dying/dead (this is called
   the ``nosrv`` case in the driver code).
 
-  With just ``UBLK_F_USER_RECOVERY`` set, after one ubq_daemon(ublk server's io
-  handler) is dying, ublk does not delete ``/dev/ublkb*`` during the whole
+  With just ``UBLK_F_USER_RECOVERY`` set, after the ublk server exits,
+  ublk does not delete ``/dev/ublkb*`` during the whole
   recovery stage and ublk device ID is kept. It is ublk server's
   responsibility to recover the device context by its own knowledge.
   Requests which have not been issued to userspace are requeued. Requests
   which have been issued to userspace are aborted.
 
-  With ``UBLK_F_USER_RECOVERY_REISSUE`` additionally set, after one ubq_daemon
-  (ublk server's io handler) is dying, contrary to ``UBLK_F_USER_RECOVERY``,
+  With ``UBLK_F_USER_RECOVERY_REISSUE`` additionally set, after the ublk server
+  exits, contrary to ``UBLK_F_USER_RECOVERY``,
   requests which have been issued to userspace are requeued and will be
   re-issued to the new process after handling ``UBLK_CMD_END_USER_RECOVERY``.
   ``UBLK_F_USER_RECOVERY_REISSUE`` is designed for backends who tolerate
@@ -241,10 +241,11 @@ can be controlled/accessed just inside this container.
 Data plane
 ----------
 
-ublk server needs to create per-queue IO pthread & io_uring for handling IO
-commands via io_uring passthrough. The per-queue IO pthread
-focuses on IO handling and shouldn't handle any control & management
-tasks.
+The ublk server should create dedicated threads for handling I/O. Each
+thread should have its own io_uring through which it is notified of new
+I/O, and through which it can complete I/O. These dedicated threads
+should focus on IO handling and shouldn't handle any control &
+management tasks.
 
 The's IO is assigned by a unique tag, which is 1:1 mapping with IO
 request of ``/dev/ublkb*``.
@@ -265,6 +266,18 @@ with specified IO tag in the command data:
   destined to ``/dev/ublkb*``. This command is sent only once from the server
   IO pthread for ublk driver to setup IO forward environment.
 
+  Once a thread issues this command against a given (qid,tag) pair, the thread
+  registers itself as that I/O's daemon. In the future, only that I/O's daemon
+  is allowed to issue commands against the I/O. If any other thread attempts
+  to issue a command against a (qid,tag) pair for which the thread is not the
+  daemon, the command will fail. Daemons can be reset only be going through
+  recovery.
+
+  The ability for every (qid,tag) pair to have its own independent daemon task
+  is indicated by the ``UBLK_F_PER_IO_DAEMON`` feature. If this feature is not
+  supported by the driver, daemons must be per-queue instead - i.e. all I/Os
+  associated to a single qid must be handled by the same task.
+
 - ``UBLK_IO_COMMIT_AND_FETCH_REQ``
 
   When an IO request is destined to ``/dev/ublkb*``, the driver stores

drivers/block/loop.c

@@ -308,11 +308,14 @@ static void lo_complete_rq(struct request *rq)
 static void lo_rw_aio_do_completion(struct loop_cmd *cmd)
 {
 	struct request *rq = blk_mq_rq_from_pdu(cmd);
+	struct loop_device *lo = rq->q->queuedata;
 
 	if (!atomic_dec_and_test(&cmd->ref))
 		return;
 	kfree(cmd->bvec);
 	cmd->bvec = NULL;
+	if (req_op(rq) == REQ_OP_WRITE)
+		file_end_write(lo->lo_backing_file);
 	if (likely(!blk_should_fake_timeout(rq->q)))
 		blk_mq_complete_request(rq);
 }
@@ -387,9 +390,10 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
 		cmd->iocb.ki_flags = 0;
 	}
 
-	if (rw == ITER_SOURCE)
+	if (rw == ITER_SOURCE) {
+		file_start_write(lo->lo_backing_file);
 		ret = file->f_op->write_iter(&cmd->iocb, &iter);
-	else
+	} else
 		ret = file->f_op->read_iter(&cmd->iocb, &iter);
 
 	lo_rw_aio_do_completion(cmd);

drivers/block/ublk_drv.c

@@ -69,7 +69,8 @@
 		| UBLK_F_USER_RECOVERY_FAIL_IO \
 		| UBLK_F_UPDATE_SIZE \
 		| UBLK_F_AUTO_BUF_REG \
-		| UBLK_F_QUIESCE)
+		| UBLK_F_QUIESCE \
+		| UBLK_F_PER_IO_DAEMON)
 
 #define UBLK_F_ALL_RECOVERY_FLAGS (UBLK_F_USER_RECOVERY \
 		| UBLK_F_USER_RECOVERY_REISSUE \
@@ -166,18 +167,18 @@ struct ublk_io {
 		/* valid if UBLK_IO_FLAG_OWNED_BY_SRV is set */
 		struct request *req;
 	};
+
+	struct task_struct *task;
 };
 
 struct ublk_queue {
 	int q_id;
 	int q_depth;
 
 	unsigned long flags;
-	struct task_struct	*ubq_daemon;
 	struct ublksrv_io_desc *io_cmd_buf;
 
 	bool force_abort;
-	bool timeout;
 	bool canceling;
 	bool fail_io; /* copy of dev->state == UBLK_S_DEV_FAIL_IO */
 	unsigned short nr_io_ready;	/* how many ios setup */
@@ -1099,11 +1100,6 @@ static inline struct ublk_uring_cmd_pdu *ublk_get_uring_cmd_pdu(
 	return io_uring_cmd_to_pdu(ioucmd, struct ublk_uring_cmd_pdu);
 }
 
-static inline bool ubq_daemon_is_dying(struct ublk_queue *ubq)
-{
-	return !ubq->ubq_daemon || ubq->ubq_daemon->flags & PF_EXITING;
-}
-
 /* todo: handle partial completion */
 static inline void __ublk_complete_rq(struct request *req)
 {
@@ -1275,13 +1271,13 @@ static void ublk_dispatch_req(struct ublk_queue *ubq,
 	/*
 	 * Task is exiting if either:
 	 *
-	 * (1) current != ubq_daemon.
+	 * (1) current != io->task.
 	 * io_uring_cmd_complete_in_task() tries to run task_work
-	 * in a workqueue if ubq_daemon(cmd's task) is PF_EXITING.
+	 * in a workqueue if cmd's task is PF_EXITING.
 	 *
 	 * (2) current->flags & PF_EXITING.
 	 */
-	if (unlikely(current != ubq->ubq_daemon || current->flags & PF_EXITING)) {
+	if (unlikely(current != io->task || current->flags & PF_EXITING)) {
 		__ublk_abort_rq(ubq, req);
 		return;
 	}
@@ -1330,38 +1326,33 @@ static void ublk_cmd_list_tw_cb(struct io_uring_cmd *cmd,
 {
 	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
 	struct request *rq = pdu->req_list;
-	struct ublk_queue *ubq = pdu->ubq;
 	struct request *next;
 
 	do {
 		next = rq->rq_next;
 		rq->rq_next = NULL;
-		ublk_dispatch_req(ubq, rq, issue_flags);
+		ublk_dispatch_req(rq->mq_hctx->driver_data, rq, issue_flags);
 		rq = next;
 	} while (rq);
 }
 
-static void ublk_queue_cmd_list(struct ublk_queue *ubq, struct rq_list *l)
+static void ublk_queue_cmd_list(struct ublk_io *io, struct rq_list *l)
 {
-	struct request *rq = rq_list_peek(l);
-	struct io_uring_cmd *cmd = ubq->ios[rq->tag].cmd;
+	struct io_uring_cmd *cmd = io->cmd;
 	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
 
-	pdu->req_list = rq;
+	pdu->req_list = rq_list_peek(l);
 	rq_list_init(l);
 	io_uring_cmd_complete_in_task(cmd, ublk_cmd_list_tw_cb);
 }
 
 static enum blk_eh_timer_return ublk_timeout(struct request *rq)
 {
 	struct ublk_queue *ubq = rq->mq_hctx->driver_data;
+	struct ublk_io *io = &ubq->ios[rq->tag];
 
 	if (ubq->flags & UBLK_F_UNPRIVILEGED_DEV) {
-		if (!ubq->timeout) {
-			send_sig(SIGKILL, ubq->ubq_daemon, 0);
-			ubq->timeout = true;
-		}
-
+		send_sig(SIGKILL, io->task, 0);
 		return BLK_EH_DONE;
 	}
 
@@ -1429,24 +1420,25 @@ static void ublk_queue_rqs(struct rq_list *rqlist)
 {
 	struct rq_list requeue_list = { };
 	struct rq_list submit_list = { };
-	struct ublk_queue *ubq = NULL;
+	struct ublk_io *io = NULL;
 	struct request *req;
 
 	while ((req = rq_list_pop(rqlist))) {
 		struct ublk_queue *this_q = req->mq_hctx->driver_data;
+		struct ublk_io *this_io = &this_q->ios[req->tag];
 
-		if (ubq && ubq != this_q && !rq_list_empty(&submit_list))
-			ublk_queue_cmd_list(ubq, &submit_list);
-		ubq = this_q;
+		if (io && io->task != this_io->task && !rq_list_empty(&submit_list))
+			ublk_queue_cmd_list(io, &submit_list);
+		io = this_io;
 
-		if (ublk_prep_req(ubq, req, true) == BLK_STS_OK)
+		if (ublk_prep_req(this_q, req, true) == BLK_STS_OK)
 			rq_list_add_tail(&submit_list, req);
 		else
 			rq_list_add_tail(&requeue_list, req);
 	}
 
-	if (ubq && !rq_list_empty(&submit_list))
-		ublk_queue_cmd_list(ubq, &submit_list);
+	if (!rq_list_empty(&submit_list))
+		ublk_queue_cmd_list(io, &submit_list);
 	*rqlist = requeue_list;
 }
 
@@ -1474,17 +1466,6 @@ static void ublk_queue_reinit(struct ublk_device *ub, struct ublk_queue *ubq)
 	/* All old ioucmds have to be completed */
 	ubq->nr_io_ready = 0;
 
-	/*
-	 * old daemon is PF_EXITING, put it now
-	 *
-	 * It could be NULL in case of closing one quisced device.
-	 */
-	if (ubq->ubq_daemon)
-		put_task_struct(ubq->ubq_daemon);
-	/* We have to reset it to NULL, otherwise ub won't accept new FETCH_REQ */
-	ubq->ubq_daemon = NULL;
-	ubq->timeout = false;
-
 	for (i = 0; i < ubq->q_depth; i++) {
 		struct ublk_io *io = &ubq->ios[i];
 
@@ -1495,6 +1476,17 @@ static void ublk_queue_reinit(struct ublk_device *ub, struct ublk_queue *ubq)
 		io->flags &= UBLK_IO_FLAG_CANCELED;
 		io->cmd = NULL;
 		io->addr = 0;
+
+		/*
+		 * old task is PF_EXITING, put it now
+		 *
+		 * It could be NULL in case of closing one quiesced
+		 * device.
+		 */
+		if (io->task) {
+			put_task_struct(io->task);
+			io->task = NULL;
+		}
 	}
 }
 
@@ -1516,7 +1508,7 @@ static void ublk_reset_ch_dev(struct ublk_device *ub)
 	for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
 		ublk_queue_reinit(ub, ublk_get_queue(ub, i));
 
-	/* set to NULL, otherwise new ubq_daemon cannot mmap the io_cmd_buf */
+	/* set to NULL, otherwise new tasks cannot mmap io_cmd_buf */
 	ub->mm = NULL;
 	ub->nr_queues_ready = 0;
 	ub->nr_privileged_daemon = 0;
@@ -1783,6 +1775,7 @@ static void ublk_uring_cmd_cancel_fn(struct io_uring_cmd *cmd,
 	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
 	struct ublk_queue *ubq = pdu->ubq;
 	struct task_struct *task;
+	struct ublk_io *io;
 
 	if (WARN_ON_ONCE(!ubq))
 		return;
@@ -1791,13 +1784,14 @@ static void ublk_uring_cmd_cancel_fn(struct io_uring_cmd *cmd,
 		return;
 
 	task = io_uring_cmd_get_task(cmd);
-	if (WARN_ON_ONCE(task && task != ubq->ubq_daemon))
+	io = &ubq->ios[pdu->tag];
+	if (WARN_ON_ONCE(task && task != io->task))
 		return;
 
 	if (!ubq->canceling)
 		ublk_start_cancel(ubq);
 
-	WARN_ON_ONCE(ubq->ios[pdu->tag].cmd != cmd);
+	WARN_ON_ONCE(io->cmd != cmd);
 	ublk_cancel_cmd(ubq, pdu->tag, issue_flags);
 }
 
@@ -1930,8 +1924,6 @@ static void ublk_mark_io_ready(struct ublk_device *ub, struct ublk_queue *ubq)
 {
 	ubq->nr_io_ready++;
 	if (ublk_queue_ready(ubq)) {
-		ubq->ubq_daemon = current;
-		get_task_struct(ubq->ubq_daemon);
 		ub->nr_queues_ready++;
 
 		if (capable(CAP_SYS_ADMIN))
@@ -2084,6 +2076,7 @@ static int ublk_fetch(struct io_uring_cmd *cmd, struct ublk_queue *ubq,
 	}
 
 	ublk_fill_io_cmd(io, cmd, buf_addr);
+	WRITE_ONCE(io->task, get_task_struct(current));
 	ublk_mark_io_ready(ub, ubq);
 out:
 	mutex_unlock(&ub->mutex);
@@ -2179,6 +2172,7 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
 			       const struct ublksrv_io_cmd *ub_cmd)
 {
 	struct ublk_device *ub = cmd->file->private_data;
+	struct task_struct *task;
 	struct ublk_queue *ubq;
 	struct ublk_io *io;
 	u32 cmd_op = cmd->cmd_op;
@@ -2193,13 +2187,14 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
 		goto out;
 
 	ubq = ublk_get_queue(ub, ub_cmd->q_id);
-	if (ubq->ubq_daemon && ubq->ubq_daemon != current)
-		goto out;
 
 	if (tag >= ubq->q_depth)
 		goto out;
 
 	io = &ubq->ios[tag];
+	task = READ_ONCE(io->task);
+	if (task && task != current)
+		goto out;
 
 	/* there is pending io cmd, something must be wrong */
 	if (io->flags & UBLK_IO_FLAG_ACTIVE) {
@@ -2449,9 +2444,14 @@ static void ublk_deinit_queue(struct ublk_device *ub, int q_id)
 {
 	int size = ublk_queue_cmd_buf_size(ub, q_id);
 	struct ublk_queue *ubq = ublk_get_queue(ub, q_id);
+	int i;
+
+	for (i = 0; i < ubq->q_depth; i++) {
+		struct ublk_io *io = &ubq->ios[i];
+		if (io->task)
+			put_task_struct(io->task);
+	}
 
-	if (ubq->ubq_daemon)
-		put_task_struct(ubq->ubq_daemon);
 	if (ubq->io_cmd_buf)
 		free_pages((unsigned long)ubq->io_cmd_buf, get_order(size));
 }
@@ -2923,7 +2923,8 @@ static int ublk_ctrl_add_dev(const struct ublksrv_ctrl_cmd *header)
 	ub->dev_info.flags &= UBLK_F_ALL;
 
 	ub->dev_info.flags |= UBLK_F_CMD_IOCTL_ENCODE |
-		UBLK_F_URING_CMD_COMP_IN_TASK;
+		UBLK_F_URING_CMD_COMP_IN_TASK |
+		UBLK_F_PER_IO_DAEMON;
 
 	/* GET_DATA isn't needed any more with USER_COPY or ZERO COPY */
 	if (ub->dev_info.flags & (UBLK_F_USER_COPY | UBLK_F_SUPPORT_ZERO_COPY |
@@ -3188,14 +3189,14 @@ static int ublk_ctrl_end_recovery(struct ublk_device *ub,
 	int ublksrv_pid = (int)header->data[0];
 	int ret = -EINVAL;
 
-	pr_devel("%s: Waiting for new ubq_daemons(nr: %d) are ready, dev id %d...\n",
-			__func__, ub->dev_info.nr_hw_queues, header->dev_id);
-	/* wait until new ubq_daemon sending all FETCH_REQ */
+	pr_devel("%s: Waiting for all FETCH_REQs, dev id %d...\n", __func__,
+		 header->dev_id);
+
 	if (wait_for_completion_interruptible(&ub->completion))
 		return -EINTR;
 
-	pr_devel("%s: All new ubq_daemons(nr: %d) are ready, dev id %d\n",
-			__func__, ub->dev_info.nr_hw_queues, header->dev_id);
+	pr_devel("%s: All FETCH_REQs received, dev id %d\n", __func__,
+		 header->dev_id);
 
 	mutex_lock(&ub->mutex);
 	if (ublk_nosrv_should_stop_dev(ub))