On Thu, Apr 10, 2025 at 01:33:11PM +0900, Damien Le Moal wrote:
> When a dm-delay devie is being suspended, the .presuspend() operation is
s/devie/device/
> first executed (delay_presuspend()) to immediately issue all the BIOs
> present in the delayed list of the device and also sets the device
> may_delay boolean to false. At the same time, any new BIO is issued to
> the device will not be delayed and immediately issued with delay_bio()
> returning DM_MAPIO_REMAPPED. This creates a situation where potentially
> 2 different contexts may be issuing write BIOs to the same zone of a
> zone device without respecting the issuing order from the user, that is,
> a newly issued write BIO may be issued before other write BIOs for the
> same target zone that are in the device delayed list. If such situation
> occurs, write BIOs may be failed by the underlying zoned device due to
> an unaligned write error.
>
> Prevent this situation from happening by always handling newly issued
> write BIOs using the delayed list of BIOs, even when the device is being
> suspended. This is done by forcing the use of the worker kthread for
> zoned devices, and by modifying flush_worker_fn() to always flush all
> delayed BIOs if the device may_delay boolean is false.
Is that scenario specific to dm-delay? I think the same applies to
any other target that supports passing on bios to zoned devices.
> spin_lock(&dc->delayed_bios_lock);
> if (unlikely(!dc->may_delay)) {
> - spin_unlock(&dc->delayed_bios_lock);
> - return DM_MAPIO_REMAPPED;
> + /*
> + * Issue the BIO immediately if the device is not zoned. FOr a
> + * zoned device, preserver the ordering of write operations by
> + * using the delay list.
> + */
> + if (!bdev_is_zoned(c->dev->bdev) || c != &dc->write) {
> + spin_unlock(&dc->delayed_bios_lock);
> + return DM_MAPIO_REMAPPED;
Don't we only need to do that if anything is queued up due to a
suspension? Then again having a different patch might be premature
optimization, it's not like anyone cares about dm-delay performance
almost by definition :)
