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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: Uday Shankar <ushankar@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250703-ublk_too_many_quiesce-v2-2-3527b5339eeb@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Uday Shankar 2025-07-03 23:41:08 -06:00 committed by Jens Axboe
parent 2fa9c93035
commit 10d77a8c60
1 changed files with 34 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

54
drivers/block/ublk_drv.c
View File

@ -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;