[PATCH v2 4/4] ublk: support device recovery without I/O queueing

[Uday Shankar <ushankar@purestorage.com>]

ublk currently supports the following behaviors on ublk server exit:

A: outstanding I/Os get errors, subsequently issued I/Os get errors
B: outstanding I/Os get errors, subsequently issued I/Os queue
C: outstanding I/Os get reissued, subsequently issued I/Os queue

and the following behaviors for recovery of preexisting block devices by
a future incarnation of the ublk server:

1: ublk devices stopped on ublk server exit (no recovery possible)
2: ublk devices are recoverable using start/end_recovery commands

The userspace interface allows selection of combinations of these
behaviors using flags specified at device creation time, namely:

default behavior: A + 1
UBLK_F_USER_RECOVERY: B + 2
UBLK_F_USER_RECOVERY|UBLK_F_USER_RECOVERY_REISSUE: C + 2

The behavior A + 2 is currently unsupported. Add support for this
behavior under the new flag combination
UBLK_F_USER_RECOVERY|UBLK_F_USER_RECOVERY_FAIL_IO.

Signed-off-by: Uday Shankar <ushankar@purestorage.com>
---
Changes since v1 (https://lore.kernel.org/linux-block/20240617194451.435445-5-ushankar@purestorage.com/):
- Change flag name from UBLK_F_USER_RECOVERY_NOQUEUE to
  UBLK_F_USER_RECOVERY_FAIL_IO
- Require UBLK_F_USER_RECOVERY to be set along with the new flag for it
  to be effective. This makes more sense, as UBLK_F_USER_RECOVERY
  essentially selects behavior 2 above (and not setting
  UBLK_F_USER_RECOVERY selects behavior 1).
- Add per-ublk-queue flag which is true iff device state is
  UBLK_S_DEV_FAIL_IO. This lets us avoid fetching the device in the fast
  path.

 drivers/block/ublk_drv.c      | 75 ++++++++++++++++++++++++++++-------
 include/uapi/linux/ublk_cmd.h | 18 +++++++++
 2 files changed, 79 insertions(+), 14 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index c7a0493b3545..548043eeefb9 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -60,10 +60,12 @@
 		| UBLK_F_UNPRIVILEGED_DEV \
 		| UBLK_F_CMD_IOCTL_ENCODE \
 		| UBLK_F_USER_COPY \
-		| UBLK_F_ZONED)
+		| UBLK_F_ZONED \
+		| UBLK_F_USER_RECOVERY_FAIL_IO)
 
 #define UBLK_F_ALL_RECOVERY_FLAGS (UBLK_F_USER_RECOVERY \
-		| UBLK_F_USER_RECOVERY_REISSUE)
+		| UBLK_F_USER_RECOVERY_REISSUE \
+		| UBLK_F_USER_RECOVERY_FAIL_IO)
 
 /* All UBLK_PARAM_TYPE_* should be included here */
 #define UBLK_PARAM_TYPE_ALL                                \
@@ -146,6 +148,7 @@ struct ublk_queue {
 	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 */
 	spinlock_t		cancel_lock;
 	struct ublk_device *dev;
@@ -690,7 +693,8 @@ static inline bool ublk_nosrv_should_reissue_outstanding(struct ublk_device *ub)
  */
 static inline bool ublk_nosrv_dev_should_queue_io(struct ublk_device *ub)
 {
-	return ub->dev_info.flags & UBLK_F_USER_RECOVERY;
+	return (ub->dev_info.flags & UBLK_F_USER_RECOVERY) &&
+	       !(ub->dev_info.flags & UBLK_F_USER_RECOVERY_FAIL_IO);
 }
 
 /*
@@ -700,7 +704,8 @@ static inline bool ublk_nosrv_dev_should_queue_io(struct ublk_device *ub)
  */
 static inline bool ublk_nosrv_should_queue_io(struct ublk_queue *ubq)
 {
-	return ubq->flags & UBLK_F_USER_RECOVERY;
+	return (ubq->flags & UBLK_F_USER_RECOVERY) &&
+	       !(ubq->flags & UBLK_F_USER_RECOVERY_FAIL_IO);
 }
 
 /*
@@ -712,7 +717,14 @@ static inline bool ublk_nosrv_should_queue_io(struct ublk_queue *ubq)
 static inline bool ublk_nosrv_should_stop_dev(struct ublk_device *ub)
 {
 	return (!(ub->dev_info.flags & UBLK_F_USER_RECOVERY)) &&
-	       (!(ub->dev_info.flags & UBLK_F_USER_RECOVERY_REISSUE));
+	       (!(ub->dev_info.flags & UBLK_F_USER_RECOVERY_REISSUE)) &&
+	       (!(ub->dev_info.flags & UBLK_F_USER_RECOVERY_FAIL_IO));
+}
+
+static inline bool ublk_dev_in_recoverable_state(struct ublk_device *ub)
+{
+	return ub->dev_info.state == UBLK_S_DEV_QUIESCED ||
+	       ub->dev_info.state == UBLK_S_DEV_FAIL_IO;
 }
 
 static void ublk_free_disk(struct gendisk *disk)
@@ -1276,6 +1288,10 @@ static blk_status_t ublk_queue_rq(struct blk_mq_hw_ctx *hctx,
 	struct request *rq = bd->rq;
 	blk_status_t res;
 
+	if (unlikely(ubq->fail_io)) {
+		return BLK_STS_TARGET;
+	}
+
 	/* fill iod to slot in io cmd buffer */
 	res = ublk_setup_iod(ubq, rq);
 	if (unlikely(res != BLK_STS_OK))
@@ -1626,6 +1642,7 @@ static void ublk_nosrv_work(struct work_struct *work)
 {
 	struct ublk_device *ub =
 		container_of(work, struct ublk_device, nosrv_work);
+	int i;
 
 	if (ublk_nosrv_should_stop_dev(ub)) {
 		ublk_stop_dev(ub);
@@ -1635,7 +1652,18 @@ static void ublk_nosrv_work(struct work_struct *work)
 	mutex_lock(&ub->mutex);
 	if (ub->dev_info.state != UBLK_S_DEV_LIVE)
 		goto unlock;
-	__ublk_quiesce_dev(ub);
+
+	if (ublk_nosrv_dev_should_queue_io(ub)) {
+		__ublk_quiesce_dev(ub);
+	} else {
+		blk_mq_quiesce_queue(ub->ub_disk->queue);
+		for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {
+			ublk_get_queue(ub, i)->fail_io = true;
+		}
+		blk_mq_unquiesce_queue(ub->ub_disk->queue);
+		ub->dev_info.state = UBLK_S_DEV_FAIL_IO;
+	}
+
  unlock:
 	mutex_unlock(&ub->mutex);
 	ublk_cancel_dev(ub);
@@ -2389,8 +2417,13 @@ static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd)
 		return -EPERM;
 
 	/* forbid nonsense combinations of recovery flags */
-	if ((info.flags & UBLK_F_USER_RECOVERY_REISSUE) &&
-	    !(info.flags & UBLK_F_USER_RECOVERY)) {
+	switch (info.flags & UBLK_F_ALL_RECOVERY_FLAGS) {
+	case 0:
+	case UBLK_F_USER_RECOVERY:
+	case (UBLK_F_USER_RECOVERY | UBLK_F_USER_RECOVERY_REISSUE):
+	case (UBLK_F_USER_RECOVERY | UBLK_F_USER_RECOVERY_FAIL_IO):
+		break;
+	default:
 		pr_warn("%s: invalid recovery flags %llx\n", __func__,
 			info.flags & UBLK_F_ALL_RECOVERY_FLAGS);
 		return -EINVAL;
@@ -2722,14 +2755,18 @@ static int ublk_ctrl_start_recovery(struct ublk_device *ub,
 	 *     and related io_uring ctx is freed so file struct of /dev/ublkcX is
 	 *     released.
 	 *
+	 * and one of the following holds
+	 *
 	 * (2) UBLK_S_DEV_QUIESCED is set, which means the quiesce_work:
 	 *     (a)has quiesced request queue
 	 *     (b)has requeued every inflight rqs whose io_flags is ACTIVE
 	 *     (c)has requeued/aborted every inflight rqs whose io_flags is NOT ACTIVE
 	 *     (d)has completed/camceled all ioucmds owned by ther dying process
+	 *
+	 * (3) UBLK_S_DEV_FAIL_IO is set, which means the queue is not
+	 *     quiesced, but all I/O is being immediately errored
 	 */
-	if (test_bit(UB_STATE_OPEN, &ub->state) ||
-			ub->dev_info.state != UBLK_S_DEV_QUIESCED) {
+	if (test_bit(UB_STATE_OPEN, &ub->state) || !ublk_dev_in_recoverable_state(ub)) {
 		ret = -EBUSY;
 		goto out_unlock;
 	}
@@ -2753,6 +2790,7 @@ static int ublk_ctrl_end_recovery(struct ublk_device *ub,
 	const struct ublksrv_ctrl_cmd *header = io_uring_sqe_cmd(cmd->sqe);
 	int ublksrv_pid = (int)header->data[0];
 	int ret = -EINVAL;
+	int i;
 
 	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);
@@ -2767,18 +2805,27 @@ static int ublk_ctrl_end_recovery(struct ublk_device *ub,
 	if (ublk_nosrv_should_stop_dev(ub))
 		goto out_unlock;
 
-	if (ub->dev_info.state != UBLK_S_DEV_QUIESCED) {
+	if (!ublk_dev_in_recoverable_state(ub)) {
 		ret = -EBUSY;
 		goto out_unlock;
 	}
 	ub->dev_info.ublksrv_pid = ublksrv_pid;
 	pr_devel("%s: new ublksrv_pid %d, dev id %d\n",
 			__func__, ublksrv_pid, header->dev_id);
+
+	blk_mq_quiesce_queue(ub->ub_disk->queue);
+	for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {
+		ublk_get_queue(ub, i)->fail_io = false;
+	}
 	blk_mq_unquiesce_queue(ub->ub_disk->queue);
-	pr_devel("%s: queue unquiesced, dev id %d.\n",
-			__func__, header->dev_id);
-	blk_mq_kick_requeue_list(ub->ub_disk->queue);
 	ub->dev_info.state = UBLK_S_DEV_LIVE;
+	if (ublk_nosrv_dev_should_queue_io(ub)) {
+		blk_mq_unquiesce_queue(ub->ub_disk->queue);
+		pr_devel("%s: queue unquiesced, dev id %d.\n",
+				__func__, header->dev_id);
+		blk_mq_kick_requeue_list(ub->ub_disk->queue);
+	}
+
 	ret = 0;
  out_unlock:
 	mutex_unlock(&ub->mutex);
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index c8dc5f8ea699..a2b3ea344639 100644
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -147,8 +147,18 @@
  */
 #define UBLK_F_NEED_GET_DATA (1UL << 2)
 
+/*
+ * - Block devices are recoverable if ublk server exits and restarts
+ * - Outstanding I/O when ublk server exits is met with errors
+ * - I/O issued while there is no ublk server queues
+ */
 #define UBLK_F_USER_RECOVERY	(1UL << 3)
 
+/*
+ * - Block devices are recoverable if ublk server exits and restarts
+ * - Outstanding I/O when ublk server exits is reissued
+ * - I/O issued while there is no ublk server queues
+ */
 #define UBLK_F_USER_RECOVERY_REISSUE	(1UL << 4)
 
 /*
@@ -184,10 +194,18 @@
  */
 #define UBLK_F_ZONED (1ULL << 8)
 
+/*
+ * - Block devices are recoverable if ublk server exits and restarts
+ * - Outstanding I/O when ublk server exits is met with errors
+ * - I/O issued while there is no ublk server is met with errors
+ */
+#define UBLK_F_USER_RECOVERY_FAIL_IO (1ULL << 9)
+
 /* device state */
 #define UBLK_S_DEV_DEAD	0
 #define UBLK_S_DEV_LIVE	1
 #define UBLK_S_DEV_QUIESCED	2
+#define UBLK_S_DEV_FAIL_IO 	3
 
 /* shipped via sqe->cmd of io_uring command */
 struct ublksrv_ctrl_cmd {
-- 
2.34.1