On Mon, 16 Dec 2013, James Bottomley wrote:
> This patch eliminates the reap_ref and replaces it with a proper kref.
> On last put of this kref, the target is removed from visibility in
> sysfs. The final call to scsi_target_reap() for the device is done from
> __scsi_remove_device() and only if the device was made visible. This
> ensures that the target disappears as soon as the last device is gone
> rather than waiting until final release of the device (which is often
> too long).
Reviewed-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Two small suggested changes:
> @@ -441,29 +466,32 @@ static struct scsi_target *scsi_alloc_target(struct device *parent,
> return starget;
>
> found:
> - found_target->reap_ref++;
> + if (!kref_get_unless_zero(&found_target->reap_ref))
> + /*
> + * release routine already fired. Target is dead, but
> + * STARGET_DEL may not yet be set (set in the release
> + * routine), so set here as well, just in case
> + */
> + found_target->state = STARGET_DEL;
> spin_unlock_irqrestore(shost->host_lock, flags);
> if (found_target->state != STARGET_DEL) {
> put_device(dev);
> return found_target;
> }
> - /* Unfortunately, we found a dying target; need to
> - * wait until it's dead before we can get a new one */
> + /*
> + * Unfortunately, we found a dying target; need to wait until it's
> + * dead before we can get a new one. There is an anomaly here. We
> + * *should* call scsi_target_reap() to balance the kref_get() of the
> + * reap_ref above. However, since the target is in state STARGET_DEL,
> + * it's already invisible and the reap_ref is irrelevant. If we call
> + * scsi_target_reap() we might spuriously do another device_del() on
> + * an already invisible target.
> + */
> put_device(&found_target->dev);
> flush_scheduled_work();
> goto retry;
Since scsi_target_reap_usercontext() is now gone, scsi_target_destroy()
doesn't rely on a work queue any more. Therefore something like
msleep(1) would be more appropriate than flush_scheduled_work().
> --- a/include/scsi/scsi_device.h
> +++ b/include/scsi/scsi_device.h
> @@ -257,7 +257,7 @@ struct scsi_target {
> struct list_head siblings;
> struct list_head devices;
> struct device dev;
> - unsigned int reap_ref; /* protected by the host lock */
> + struct kref reap_ref; /* last put renders device invisible */
s/device/target/
Alan Stern
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