On Wed, 14 Mar 2012, Dan Williams wrote: > libsas power management routines to suspend and recover the sas domain > based on a model where the lldd is allowed and expected to be > "forgetful". What exactly does that mean? What is there for the lldd to remember? Does it maintain some sort of state information about the devices attached to the links? > sas_suspend_ha - disable event processing allowing the lldd to take down > links without concern for causing hotplug events. > Regardless of whether the lldd actually posts link down > messages libsas notifies the lldd that all > domain_devices are gone. > > sas_prep_resume_ha - on the way back up before the lldd starts link > training clean out any spurious events that were > generated on the way down, and re-enable event > processing > > sas_resume_ha - after the lldd has started and decided that all phys > have posted link-up events this routine is called to let > libsas start it's own timeout of any phys that did not > resume. After the timeout an lldd can cancel the > phy teardown by posting a link-up event. > > Storage for ex_change_count (u16) and phy_change_count (u8) are changed > to int so they can be set to -1 to indicate 'invalidated'. > > There's a hack added to sas_destruct_devices to workaround a deadlock > when a device is removed across the suspend cycle. sd_remove is called > under device_lock() and wants to async_synchronize_full(), while the > resume path is running in an async callback and is trying to grab > device_lock()... fun ensues. So we guarantee that async resume actions > have been flushed before allowing new invocations of sd_remove. Ooh, that doesn't sound like a good way to handle it. For one thing, it's possible for the resume routine to be called while the caller holds the device-lock for the device being resumed. It would be best if the resume path defers removal of devices that have disappeared to a different thread. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
