Commit 10d77a8c authored by Uday Shankar's avatar Uday Shankar Committed by Jens Axboe
Browse files

ublk: introduce and use ublk_set_canceling helper 



For performance reasons (minimizing the number of cache lines accessed
in the hot path), we store the "canceling" state redundantly - there is
one flag in the device, which can be considered the source of truth, and
per-queue copies of that flag. This redundancy can cause confusion, and
opens the door to bugs where the state is set inconsistently. Try to
guard against these bugs by introducing a ublk_set_canceling helper
which is the sole mutator of both the per-device and per-queue canceling
state. This helper always sets the state consistently. Use the helper in
all places where we need to modify the canceling state.

No functional changes are expected.

Signed-off-by: default avatarUday Shankar <ushankar@purestorage.com>
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250703-ublk_too_many_quiesce-v2-2-3527b5339eeb@purestorage.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 2fa9c930

drivers/block/ublk_drv.c

+34 −20
Original line number Diff line number Diff line
@@ -1563,6 +1563,27 @@ static void ublk_put_disk(struct gendisk *disk) 
		put_device(disk_to_dev(disk));

}



/*

 * Use this function to ensure that ->canceling is consistently set for

 * the device and all queues. Do not set these flags directly.

 *

 * Caller must ensure that:

 * - cancel_mutex is held. This ensures that there is no concurrent

 *   access to ub->canceling and no concurrent writes to ubq->canceling.

 * - there are no concurrent reads of ubq->canceling from the queue_rq

 *   path. This can be done by quiescing the queue, or through other

 *   means.

 */

static void ublk_set_canceling(struct ublk_device *ub, bool canceling)

	__must_hold(&ub->cancel_mutex)

{

	int i;



	ub->canceling = canceling;

	for (i = 0; i < ub->dev_info.nr_hw_queues; i++)

		ublk_get_queue(ub, i)->canceling = canceling;

}



static int ublk_ch_release(struct inode *inode, struct file *filp)

{

	struct ublk_device *ub = filp->private_data;
@@ -1591,13 +1612,11 @@ static int ublk_ch_release(struct inode *inode, struct file *filp) 
	 * All requests may be inflight, so ->canceling may not be set, set

	 * it now.

	 */

	ub->canceling = true;

	for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {

		struct ublk_queue *ubq = ublk_get_queue(ub, i);



		ubq->canceling = true;

		ublk_abort_queue(ub, ubq);

	}

	mutex_lock(&ub->cancel_mutex);

	ublk_set_canceling(ub, true);

	for (i = 0; i < ub->dev_info.nr_hw_queues; i++)

		ublk_abort_queue(ub, ublk_get_queue(ub, i));

	mutex_unlock(&ub->cancel_mutex);

	blk_mq_kick_requeue_list(disk->queue);



	/*
@@ -1723,7 +1742,6 @@ static void ublk_abort_queue(struct ublk_device *ub, struct ublk_queue *ubq) 
static void ublk_start_cancel(struct ublk_device *ub)

{

	struct gendisk *disk = ublk_get_disk(ub);

	int i;



	/* Our disk has been dead */

	if (!disk)
@@ -1740,9 +1758,7 @@ static void ublk_start_cancel(struct ublk_device *ub) 
	 * touch completed uring_cmd

	 */

	blk_mq_quiesce_queue(disk->queue);

	ub->canceling = true;

	for (i = 0; i < ub->dev_info.nr_hw_queues; i++)

		ublk_get_queue(ub, i)->canceling = true;

	ublk_set_canceling(ub, true);

	blk_mq_unquiesce_queue(disk->queue);

out:

	mutex_unlock(&ub->cancel_mutex);
@@ -1942,10 +1958,11 @@ static void ublk_reset_io_flags(struct ublk_device *ub) 
		for (j = 0; j < ubq->q_depth; j++)

			ubq->ios[j].flags &= ~UBLK_IO_FLAG_CANCELED;

		spin_unlock(&ubq->cancel_lock);

		ubq->canceling = false;

		ubq->fail_io = false;

	}

	ub->canceling = false;

	mutex_lock(&ub->cancel_mutex);

	ublk_set_canceling(ub, false);

	mutex_unlock(&ub->cancel_mutex);

}



/* device can only be started after all IOs are ready */
@@ -3417,7 +3434,7 @@ static int ublk_ctrl_quiesce_dev(struct ublk_device *ub, 
	/* zero means wait forever */

	u64 timeout_ms = header->data[0];

	struct gendisk *disk;

	int i, ret = -ENODEV;

	int ret = -ENODEV;



	if (!(ub->dev_info.flags & UBLK_F_QUIESCE))

		return -EOPNOTSUPP;
@@ -3435,14 +3452,11 @@ static int ublk_ctrl_quiesce_dev(struct ublk_device *ub, 
		goto put_disk;



	/* Mark the device as canceling */

	mutex_lock(&ub->cancel_mutex);

	blk_mq_quiesce_queue(disk->queue);

	ub->canceling = true;

	for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {

		struct ublk_queue *ubq = ublk_get_queue(ub, i);



		ubq->canceling = true;

	}

	ublk_set_canceling(ub, true);

	blk_mq_unquiesce_queue(disk->queue);

	mutex_unlock(&ub->cancel_mutex);



	if (!timeout_ms)

		timeout_ms = UINT_MAX;