[PATCH V3 0/2] ublk: avoid ublk_io_release() called after ublk char dev is closed

[PATCH V3 0/2] ublk: avoid ublk_io_release() called after ublk char dev is closed

[Ming Lei]

Hi Jens,

The 1st patch fixes ublk_io_release(), and avoids warning from ublk
selftest(test_stress_04.sh).

The 2nd patch adds test case for this issue.

V3:
- move reference counter reset into the check helper(Caleb Sander Mateos)
- remove 'ub' re-assignment in ublk_ch_release() (Caleb Sander Mateos)
- improve commit log

V2:
- release ublk char device in async way for avoiding dependency with
io_uring_release(), where sqe buffers may be unregistered finally


Ming Lei (2):
  ublk: avoid ublk_io_release() called after ublk char dev is closed
  ublk selftests: add --no_ublk_fixed_fd for not using registered ublk
    char device

 drivers/block/ublk_drv.c                      | 72 ++++++++++++++++++-
 tools/testing/selftests/ublk/file_backed.c    | 10 +--
 tools/testing/selftests/ublk/kublk.c          | 38 ++++++++--
 tools/testing/selftests/ublk/kublk.h          | 45 ++++++++----
 tools/testing/selftests/ublk/null.c           |  4 +-
 tools/testing/selftests/ublk/stripe.c         |  4 +-
 .../testing/selftests/ublk/test_stress_04.sh  |  6 +-
 7 files changed, 144 insertions(+), 35 deletions(-)

-- 
2.47.0

[PATCH V3 1/2] ublk: avoid ublk_io_release() called after ublk char dev is closed

[Ming Lei]

When running test_stress_04.sh, the following warning is triggered:

WARNING: CPU: 1 PID: 135 at drivers/block/ublk_drv.c:1933 ublk_ch_release+0x423/0x4b0 [ublk_drv]

This happens when the daemon is abruptly killed:

- some references may still be held, because registering IO buffer
doesn't grab ublk char device reference

OR

- io->task_registered_buffers won't be cleared because io buffer is
released from non-daemon context

For zero-copy and auto buffer register modes, I/O reference crosses
syscalls, so IO reference may not be dropped naturally when ublk server is
killed abruptly. However, when releasing io_uring context, it is guaranteed
that the reference is dropped finally, see io_sqe_buffers_unregister() from
io_ring_ctx_free().

Fix this by adding ublk_drain_io_references() that:
- Waits for active I/O references dropped in async way by scheduling
  work function, for avoiding ublk dev and io_uring file's release
  dependency
- Reinitializes io->ref and io->task_registered_buffers to clean state

This ensures the reference count state is clean when ublk_queue_reinit()
is called, preventing the warning and potential use-after-free.

Fixes: 1f6540e2aabb ("ublk: zc register/unregister bvec")
Fixes: 1ceeedb59749 ("ublk: optimize UBLK_IO_UNREGISTER_IO_BUF on daemon task")
Fixes: 8a8fe42d765b ("ublk: optimize UBLK_IO_REGISTER_IO_BUF on daemon task")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/block/ublk_drv.c | 72 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 70 insertions(+), 2 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 99abd67b708b..67d4a867aec4 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -239,6 +239,7 @@ struct ublk_device {
 	struct mutex cancel_mutex;
 	bool canceling;
 	pid_t 	ublksrv_tgid;
+	struct delayed_work	exit_work;
 };
 
 /* header of ublk_params */
@@ -1595,12 +1596,62 @@ static void ublk_set_canceling(struct ublk_device *ub, bool canceling)
 		ublk_get_queue(ub, i)->canceling = canceling;
 }
 
-static int ublk_ch_release(struct inode *inode, struct file *filp)
+static bool ublk_check_and_reset_active_ref(struct ublk_device *ub)
 {
-	struct ublk_device *ub = filp->private_data;
+	int i, j;
+
+	if (!(ub->dev_info.flags & (UBLK_F_SUPPORT_ZERO_COPY |
+					UBLK_F_AUTO_BUF_REG)))
+		return false;
+
+	for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {
+		struct ublk_queue *ubq = ublk_get_queue(ub, i);
+
+		for (j = 0; j < ubq->q_depth; j++) {
+			struct ublk_io *io = &ubq->ios[j];
+			unsigned int refs = refcount_read(&io->ref) +
+				io->task_registered_buffers;
+
+			/*
+			 * UBLK_REFCOUNT_INIT or zero means no active
+			 * reference
+			 */
+			if (refs != UBLK_REFCOUNT_INIT && refs != 0)
+				return true;
+
+			/* reset to zero if the io hasn't active references */
+			refcount_set(&io->ref, 0);
+			io->task_registered_buffers = 0;
+		}
+	}
+	return false;
+}
+
+static void ublk_ch_release_work_fn(struct work_struct *work)
+{
+	struct ublk_device *ub =
+		container_of(work, struct ublk_device, exit_work.work);
 	struct gendisk *disk;
 	int i;
 
+	/*
+	 * For zero-copy and auto buffer register modes, I/O references
+	 * might not be dropped naturally when the daemon is killed, but
+	 * io_uring guarantees that registered bvec kernel buffers are
+	 * unregistered finally when freeing io_uring context, then the
+	 * active references are dropped.
+	 *
+	 * Wait until active references are dropped for avoiding use-after-free
+	 *
+	 * registered buffer may be unregistered in io_ring's release hander,
+	 * so have to wait by scheduling work function for avoiding the two
+	 * file release dependency.
+	 */
+	if (ublk_check_and_reset_active_ref(ub)) {
+		schedule_delayed_work(&ub->exit_work, 1);
+		return;
+	}
+
 	/*
 	 * disk isn't attached yet, either device isn't live, or it has
 	 * been removed already, so we needn't to do anything
@@ -1673,6 +1724,23 @@ static int ublk_ch_release(struct inode *inode, struct file *filp)
 	ublk_reset_ch_dev(ub);
 out:
 	clear_bit(UB_STATE_OPEN, &ub->state);
+
+	/* put the reference grabbed in ublk_ch_release() */
+	ublk_put_device(ub);
+}
+
+static int ublk_ch_release(struct inode *inode, struct file *filp)
+{
+	struct ublk_device *ub = filp->private_data;
+
+	/*
+	 * Grab ublk device reference, so it won't be gone until we are
+	 * really released from work function.
+	 */
+	ublk_get_device(ub);
+
+	INIT_DELAYED_WORK(&ub->exit_work, ublk_ch_release_work_fn);
+	schedule_delayed_work(&ub->exit_work, 0);
 	return 0;
 }
 
-- 
2.47.0

[PATCH V3 2/2] ublk selftests: add --no_ublk_fixed_fd for not using registered ublk char device

[Ming Lei]

Add a new command line option --no_ublk_fixed_fd that excludes the ublk
control device (/dev/ublkcN) from io_uring's registered files array.
When this option is used, only backing files are registered starting
from index 1, while the ublk control device is accessed using its raw
file descriptor.

Add ublk_get_registered_fd() helper function that returns the appropriate
file descriptor for use with io_uring operations.

Key optimizations implemented:
- Cache UBLKS_Q_NO_UBLK_FIXED_FD flag in ublk_queue.flags to avoid
  reading dev->no_ublk_fixed_fd in fast path
- Cache ublk char device fd in ublk_queue.ublk_fd for fast access
- Update ublk_get_registered_fd() to use ublk_queue * parameter
- Update io_uring_prep_buf_register/unregister() to use ublk_queue *
- Replace ublk_device * access with ublk_queue * access in fast paths

Also pass --no_ublk_fixed_fd to test_stress_04.sh for covering
plain ublk char device mode.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 tools/testing/selftests/ublk/file_backed.c    | 10 ++---
 tools/testing/selftests/ublk/kublk.c          | 38 +++++++++++++---
 tools/testing/selftests/ublk/kublk.h          | 45 +++++++++++++------
 tools/testing/selftests/ublk/null.c           |  4 +-
 tools/testing/selftests/ublk/stripe.c         |  4 +-
 .../testing/selftests/ublk/test_stress_04.sh  |  6 +--
 6 files changed, 74 insertions(+), 33 deletions(-)

diff --git a/tools/testing/selftests/ublk/file_backed.c b/tools/testing/selftests/ublk/file_backed.c
index 2d93ac860bd5..cd9fe69ecce2 100644
--- a/tools/testing/selftests/ublk/file_backed.c
+++ b/tools/testing/selftests/ublk/file_backed.c
@@ -20,7 +20,7 @@ static int loop_queue_flush_io(struct ublk_thread *t, struct ublk_queue *q,
 	struct io_uring_sqe *sqe[1];
 
 	ublk_io_alloc_sqes(t, sqe, 1);
-	io_uring_prep_fsync(sqe[0], 1 /*fds[1]*/, IORING_FSYNC_DATASYNC);
+	io_uring_prep_fsync(sqe[0], ublk_get_registered_fd(q, 1) /*fds[1]*/, IORING_FSYNC_DATASYNC);
 	io_uring_sqe_set_flags(sqe[0], IOSQE_FIXED_FILE);
 	/* bit63 marks us as tgt io */
 	sqe[0]->user_data = build_user_data(tag, ublk_op, 0, q->q_id, 1);
@@ -42,7 +42,7 @@ static int loop_queue_tgt_rw_io(struct ublk_thread *t, struct ublk_queue *q,
 		if (!sqe[0])
 			return -ENOMEM;
 
-		io_uring_prep_rw(op, sqe[0], 1 /*fds[1]*/,
+		io_uring_prep_rw(op, sqe[0], ublk_get_registered_fd(q, 1) /*fds[1]*/,
 				addr,
 				iod->nr_sectors << 9,
 				iod->start_sector << 9);
@@ -56,19 +56,19 @@ static int loop_queue_tgt_rw_io(struct ublk_thread *t, struct ublk_queue *q,
 
 	ublk_io_alloc_sqes(t, sqe, 3);
 
-	io_uring_prep_buf_register(sqe[0], 0, tag, q->q_id, ublk_get_io(q, tag)->buf_index);
+	io_uring_prep_buf_register(sqe[0], q, tag, q->q_id, ublk_get_io(q, tag)->buf_index);
 	sqe[0]->flags |= IOSQE_CQE_SKIP_SUCCESS | IOSQE_IO_HARDLINK;
 	sqe[0]->user_data = build_user_data(tag,
 			ublk_cmd_op_nr(sqe[0]->cmd_op), 0, q->q_id, 1);
 
-	io_uring_prep_rw(op, sqe[1], 1 /*fds[1]*/, 0,
+	io_uring_prep_rw(op, sqe[1], ublk_get_registered_fd(q, 1) /*fds[1]*/, 0,
 		iod->nr_sectors << 9,
 		iod->start_sector << 9);
 	sqe[1]->buf_index = tag;
 	sqe[1]->flags |= IOSQE_FIXED_FILE | IOSQE_IO_HARDLINK;
 	sqe[1]->user_data = build_user_data(tag, ublk_op, 0, q->q_id, 1);
 
-	io_uring_prep_buf_unregister(sqe[2], 0, tag, q->q_id, ublk_get_io(q, tag)->buf_index);
+	io_uring_prep_buf_unregister(sqe[2], q, tag, q->q_id, ublk_get_io(q, tag)->buf_index);
 	sqe[2]->user_data = build_user_data(tag, ublk_cmd_op_nr(sqe[2]->cmd_op), 0, q->q_id, 1);
 
 	return 2;
diff --git a/tools/testing/selftests/ublk/kublk.c b/tools/testing/selftests/ublk/kublk.c
index 6512dfbdbce3..b71faba86c3b 100644
--- a/tools/testing/selftests/ublk/kublk.c
+++ b/tools/testing/selftests/ublk/kublk.c
@@ -432,7 +432,7 @@ static void ublk_thread_deinit(struct ublk_thread *t)
 	}
 }
 
-static int ublk_queue_init(struct ublk_queue *q, unsigned extra_flags)
+static int ublk_queue_init(struct ublk_queue *q, unsigned long long extra_flags)
 {
 	struct ublk_dev *dev = q->dev;
 	int depth = dev->dev_info.queue_depth;
@@ -446,6 +446,9 @@ static int ublk_queue_init(struct ublk_queue *q, unsigned extra_flags)
 	q->flags = dev->dev_info.flags;
 	q->flags |= extra_flags;
 
+	/* Cache fd in queue for fast path access */
+	q->ublk_fd = dev->fds[0];
+
 	cmd_buf_size = ublk_queue_cmd_buf_sz(q);
 	off = UBLKSRV_CMD_BUF_OFFSET + q->q_id * ublk_queue_max_cmd_buf_sz();
 	q->io_cmd_buf = mmap(0, cmd_buf_size, PROT_READ,
@@ -481,9 +484,10 @@ static int ublk_queue_init(struct ublk_queue *q, unsigned extra_flags)
 	return -ENOMEM;
 }
 
-static int ublk_thread_init(struct ublk_thread *t)
+static int ublk_thread_init(struct ublk_thread *t, unsigned long long extra_flags)
 {
 	struct ublk_dev *dev = t->dev;
+	unsigned long long flags = dev->dev_info.flags | extra_flags;
 	int ring_depth = dev->tgt.sq_depth, cq_depth = dev->tgt.cq_depth;
 	int ret;
 
@@ -512,7 +516,17 @@ static int ublk_thread_init(struct ublk_thread *t)
 
 	io_uring_register_ring_fd(&t->ring);
 
-	ret = io_uring_register_files(&t->ring, dev->fds, dev->nr_fds);
+	if (flags & UBLKS_Q_NO_UBLK_FIXED_FD) {
+		/* Register only backing files starting from index 1, exclude ublk control device */
+		if (dev->nr_fds > 1) {
+			ret = io_uring_register_files(&t->ring, &dev->fds[1], dev->nr_fds - 1);
+		} else {
+			/* No backing files to register, skip file registration */
+			ret = 0;
+		}
+	} else {
+		ret = io_uring_register_files(&t->ring, dev->fds, dev->nr_fds);
+	}
 	if (ret) {
 		ublk_err("ublk dev %d thread %d register files failed %d\n",
 				t->dev->dev_info.dev_id, t->idx, ret);
@@ -626,9 +640,12 @@ int ublk_queue_io_cmd(struct ublk_thread *t, struct ublk_io *io)
 
 	/* These fields should be written once, never change */
 	ublk_set_sqe_cmd_op(sqe[0], cmd_op);
-	sqe[0]->fd		= 0;	/* dev->fds[0] */
+	sqe[0]->fd	= ublk_get_registered_fd(q, 0);	/* dev->fds[0] */
 	sqe[0]->opcode	= IORING_OP_URING_CMD;
-	sqe[0]->flags	= IOSQE_FIXED_FILE;
+	if (q->flags & UBLKS_Q_NO_UBLK_FIXED_FD)
+		sqe[0]->flags	= 0;  /* Use raw FD, not fixed file */
+	else
+		sqe[0]->flags	= IOSQE_FIXED_FILE;
 	sqe[0]->rw_flags	= 0;
 	cmd->tag	= io->tag;
 	cmd->q_id	= q->q_id;
@@ -832,6 +849,7 @@ struct ublk_thread_info {
 	unsigned		idx;
 	sem_t 			*ready;
 	cpu_set_t 		*affinity;
+	unsigned long long	extra_flags;
 };
 
 static void *ublk_io_handler_fn(void *data)
@@ -844,7 +862,7 @@ static void *ublk_io_handler_fn(void *data)
 	t->dev = info->dev;
 	t->idx = info->idx;
 
-	ret = ublk_thread_init(t);
+	ret = ublk_thread_init(t, info->extra_flags);
 	if (ret) {
 		ublk_err("ublk dev %d thread %u init failed\n",
 				dev_id, t->idx);
@@ -934,6 +952,8 @@ static int ublk_start_daemon(const struct dev_ctx *ctx, struct ublk_dev *dev)
 
 	if (ctx->auto_zc_fallback)
 		extra_flags = UBLKS_Q_AUTO_BUF_REG_FALLBACK;
+	if (ctx->no_ublk_fixed_fd)
+		extra_flags |= UBLKS_Q_NO_UBLK_FIXED_FD;
 
 	for (i = 0; i < dinfo->nr_hw_queues; i++) {
 		dev->q[i].dev = dev;
@@ -951,6 +971,7 @@ static int ublk_start_daemon(const struct dev_ctx *ctx, struct ublk_dev *dev)
 		tinfo[i].dev = dev;
 		tinfo[i].idx = i;
 		tinfo[i].ready = &ready;
+		tinfo[i].extra_flags = extra_flags;
 
 		/*
 		 * If threads are not tied 1:1 to queues, setting thread
@@ -1471,7 +1492,7 @@ static void __cmd_create_help(char *exe, bool recovery)
 	printf("%s %s -t [null|loop|stripe|fault_inject] [-q nr_queues] [-d depth] [-n dev_id]\n",
 			exe, recovery ? "recover" : "add");
 	printf("\t[--foreground] [--quiet] [-z] [--auto_zc] [--auto_zc_fallback] [--debug_mask mask] [-r 0|1 ] [-g]\n");
-	printf("\t[-e 0|1 ] [-i 0|1]\n");
+	printf("\t[-e 0|1 ] [-i 0|1] [--no_ublk_fixed_fd]\n");
 	printf("\t[--nthreads threads] [--per_io_tasks]\n");
 	printf("\t[target options] [backfile1] [backfile2] ...\n");
 	printf("\tdefault: nr_queues=2(max 32), depth=128(max 1024), dev_id=-1(auto allocation)\n");
@@ -1534,6 +1555,7 @@ int main(int argc, char *argv[])
 		{ "size",		1,	NULL, 's'},
 		{ "nthreads",		1,	NULL,  0 },
 		{ "per_io_tasks",	0,	NULL,  0 },
+		{ "no_ublk_fixed_fd",	0,	NULL,  0 },
 		{ 0, 0, 0, 0 }
 	};
 	const struct ublk_tgt_ops *ops = NULL;
@@ -1613,6 +1635,8 @@ int main(int argc, char *argv[])
 				ctx.nthreads = strtol(optarg, NULL, 10);
 			if (!strcmp(longopts[option_idx].name, "per_io_tasks"))
 				ctx.per_io_tasks = 1;
+			if (!strcmp(longopts[option_idx].name, "no_ublk_fixed_fd"))
+				ctx.no_ublk_fixed_fd = 1;
 			break;
 		case '?':
 			/*
diff --git a/tools/testing/selftests/ublk/kublk.h b/tools/testing/selftests/ublk/kublk.h
index 219233f8a053..5e55484fb0aa 100644
--- a/tools/testing/selftests/ublk/kublk.h
+++ b/tools/testing/selftests/ublk/kublk.h
@@ -77,6 +77,7 @@ struct dev_ctx {
 	unsigned int	recovery:1;
 	unsigned int	auto_zc_fallback:1;
 	unsigned int	per_io_tasks:1;
+	unsigned int	no_ublk_fixed_fd:1;
 
 	int _evtfd;
 	int _shmid;
@@ -166,7 +167,9 @@ struct ublk_queue {
 
 /* borrow one bit of ublk uapi flags, which may never be used */
 #define UBLKS_Q_AUTO_BUF_REG_FALLBACK	(1ULL << 63)
+#define UBLKS_Q_NO_UBLK_FIXED_FD	(1ULL << 62)
 	__u64 flags;
+	int ublk_fd;	/* cached ublk char device fd */
 	struct ublk_io ios[UBLK_QUEUE_DEPTH];
 };
 
@@ -273,34 +276,48 @@ static inline int ublk_io_alloc_sqes(struct ublk_thread *t,
 	return nr_sqes;
 }
 
-static inline void io_uring_prep_buf_register(struct io_uring_sqe *sqe,
-		int dev_fd, int tag, int q_id, __u64 index)
+static inline int ublk_get_registered_fd(struct ublk_queue *q, int fd_index)
+{
+	if (q->flags & UBLKS_Q_NO_UBLK_FIXED_FD) {
+		if (fd_index == 0)
+			/* Return the raw ublk FD for index 0 */
+			return q->ublk_fd;
+		/* Adjust index for backing files (index 1 becomes 0, etc.) */
+		return fd_index - 1;
+	}
+	return fd_index;
+}
+
+static inline void __io_uring_prep_buf_reg_unreg(struct io_uring_sqe *sqe,
+		struct ublk_queue *q, int tag, int q_id, __u64 index)
 {
 	struct ublksrv_io_cmd *cmd = (struct ublksrv_io_cmd *)sqe->cmd;
+	int dev_fd = ublk_get_registered_fd(q, 0);
 
 	io_uring_prep_read(sqe, dev_fd, 0, 0, 0);
 	sqe->opcode		= IORING_OP_URING_CMD;
-	sqe->flags		|= IOSQE_FIXED_FILE;
-	sqe->cmd_op		= UBLK_U_IO_REGISTER_IO_BUF;
+	if (q->flags & UBLKS_Q_NO_UBLK_FIXED_FD)
+		sqe->flags	&= ~IOSQE_FIXED_FILE;
+	else
+		sqe->flags	|= IOSQE_FIXED_FILE;
 
 	cmd->tag		= tag;
 	cmd->addr		= index;
 	cmd->q_id		= q_id;
 }
 
-static inline void io_uring_prep_buf_unregister(struct io_uring_sqe *sqe,
-		int dev_fd, int tag, int q_id, __u64 index)
+static inline void io_uring_prep_buf_register(struct io_uring_sqe *sqe,
+		struct ublk_queue *q, int tag, int q_id, __u64 index)
 {
-	struct ublksrv_io_cmd *cmd = (struct ublksrv_io_cmd *)sqe->cmd;
+	__io_uring_prep_buf_reg_unreg(sqe, q, tag, q_id, index);
+	sqe->cmd_op		= UBLK_U_IO_REGISTER_IO_BUF;
+}
 
-	io_uring_prep_read(sqe, dev_fd, 0, 0, 0);
-	sqe->opcode		= IORING_OP_URING_CMD;
-	sqe->flags		|= IOSQE_FIXED_FILE;
+static inline void io_uring_prep_buf_unregister(struct io_uring_sqe *sqe,
+		struct ublk_queue *q, int tag, int q_id, __u64 index)
+{
+	__io_uring_prep_buf_reg_unreg(sqe, q, tag, q_id, index);
 	sqe->cmd_op		= UBLK_U_IO_UNREGISTER_IO_BUF;
-
-	cmd->tag		= tag;
-	cmd->addr		= index;
-	cmd->q_id		= q_id;
 }
 
 static inline void *ublk_get_sqe_cmd(const struct io_uring_sqe *sqe)
diff --git a/tools/testing/selftests/ublk/null.c b/tools/testing/selftests/ublk/null.c
index f0e0003a4860..280043f6b689 100644
--- a/tools/testing/selftests/ublk/null.c
+++ b/tools/testing/selftests/ublk/null.c
@@ -63,7 +63,7 @@ static int null_queue_zc_io(struct ublk_thread *t, struct ublk_queue *q,
 
 	ublk_io_alloc_sqes(t, sqe, 3);
 
-	io_uring_prep_buf_register(sqe[0], 0, tag, q->q_id, ublk_get_io(q, tag)->buf_index);
+	io_uring_prep_buf_register(sqe[0], q, tag, q->q_id, ublk_get_io(q, tag)->buf_index);
 	sqe[0]->user_data = build_user_data(tag,
 			ublk_cmd_op_nr(sqe[0]->cmd_op), 0, q->q_id, 1);
 	sqe[0]->flags |= IOSQE_CQE_SKIP_SUCCESS | IOSQE_IO_HARDLINK;
@@ -71,7 +71,7 @@ static int null_queue_zc_io(struct ublk_thread *t, struct ublk_queue *q,
 	__setup_nop_io(tag, iod, sqe[1], q->q_id);
 	sqe[1]->flags |= IOSQE_IO_HARDLINK;
 
-	io_uring_prep_buf_unregister(sqe[2], 0, tag, q->q_id, ublk_get_io(q, tag)->buf_index);
+	io_uring_prep_buf_unregister(sqe[2], q, tag, q->q_id, ublk_get_io(q, tag)->buf_index);
 	sqe[2]->user_data = build_user_data(tag, ublk_cmd_op_nr(sqe[2]->cmd_op), 0, q->q_id, 1);
 
 	// buf register is marked as IOSQE_CQE_SKIP_SUCCESS
diff --git a/tools/testing/selftests/ublk/stripe.c b/tools/testing/selftests/ublk/stripe.c
index 1fb9b7cc281b..791fa8dc1651 100644
--- a/tools/testing/selftests/ublk/stripe.c
+++ b/tools/testing/selftests/ublk/stripe.c
@@ -142,7 +142,7 @@ static int stripe_queue_tgt_rw_io(struct ublk_thread *t, struct ublk_queue *q,
 	ublk_io_alloc_sqes(t, sqe, s->nr + extra);
 
 	if (zc) {
-		io_uring_prep_buf_register(sqe[0], 0, tag, q->q_id, io->buf_index);
+		io_uring_prep_buf_register(sqe[0], q, tag, q->q_id, io->buf_index);
 		sqe[0]->flags |= IOSQE_CQE_SKIP_SUCCESS | IOSQE_IO_HARDLINK;
 		sqe[0]->user_data = build_user_data(tag,
 			ublk_cmd_op_nr(sqe[0]->cmd_op), 0, q->q_id, 1);
@@ -168,7 +168,7 @@ static int stripe_queue_tgt_rw_io(struct ublk_thread *t, struct ublk_queue *q,
 	if (zc) {
 		struct io_uring_sqe *unreg = sqe[s->nr + 1];
 
-		io_uring_prep_buf_unregister(unreg, 0, tag, q->q_id, io->buf_index);
+		io_uring_prep_buf_unregister(unreg, q, tag, q->q_id, io->buf_index);
 		unreg->user_data = build_user_data(
 			tag, ublk_cmd_op_nr(unreg->cmd_op), 0, q->q_id, 1);
 	}
diff --git a/tools/testing/selftests/ublk/test_stress_04.sh b/tools/testing/selftests/ublk/test_stress_04.sh
index 40d1437ca298..3f901db4d09d 100755
--- a/tools/testing/selftests/ublk/test_stress_04.sh
+++ b/tools/testing/selftests/ublk/test_stress_04.sh
@@ -28,14 +28,14 @@ _create_backfile 0 256M
 _create_backfile 1 128M
 _create_backfile 2 128M
 
-ublk_io_and_kill_daemon 8G -t null -q 4 -z &
-ublk_io_and_kill_daemon 256M -t loop -q 4 -z "${UBLK_BACKFILES[0]}" &
+ublk_io_and_kill_daemon 8G -t null -q 4 -z --no_ublk_fixed_fd &
+ublk_io_and_kill_daemon 256M -t loop -q 4 -z --no_ublk_fixed_fd "${UBLK_BACKFILES[0]}" &
 ublk_io_and_kill_daemon 256M -t stripe -q 4 -z "${UBLK_BACKFILES[1]}" "${UBLK_BACKFILES[2]}" &
 
 if _have_feature "AUTO_BUF_REG"; then
 	ublk_io_and_kill_daemon 8G -t null -q 4 --auto_zc &
 	ublk_io_and_kill_daemon 256M -t loop -q 4 --auto_zc "${UBLK_BACKFILES[0]}" &
-	ublk_io_and_kill_daemon 256M -t stripe -q 4 --auto_zc "${UBLK_BACKFILES[1]}" "${UBLK_BACKFILES[2]}" &
+	ublk_io_and_kill_daemon 256M -t stripe -q 4 --auto_zc --no_ublk_fixed_fd "${UBLK_BACKFILES[1]}" "${UBLK_BACKFILES[2]}" &
 	ublk_io_and_kill_daemon 8G -t null -q 4 -z --auto_zc --auto_zc_fallback &
 fi
 
-- 
2.47.0

Re: [PATCH V3 0/2] ublk: avoid ublk_io_release() called after ublk char dev is closed

[Jens Axboe]

On Wed, 27 Aug 2025 20:15:58 +0800, Ming Lei wrote:
> The 1st patch fixes ublk_io_release(), and avoids warning from ublk
> selftest(test_stress_04.sh).
> 
> The 2nd patch adds test case for this issue.
> 
> V3:
> - move reference counter reset into the check helper(Caleb Sander Mateos)
> - remove 'ub' re-assignment in ublk_ch_release() (Caleb Sander Mateos)
> - improve commit log
> 
> [...]

Applied, thanks!

[1/2] ublk: avoid ublk_io_release() called after ublk char dev is closed
      commit: c5c5eb24ed6177fc0ef4bb75fc18d07a99c1d3f0
[2/2] ublk selftests: add --no_ublk_fixed_fd for not using registered ublk char device
      commit: 9b2785ea8592f239836405de023c75c4f3f5ce00

Best regards,
-- 
Jens Axboe