Re: [RFC/PATCH] ubi: Replace wear leveling thread with a workqueue

Ezequiel Garcia
2012-11-23T23:42:36Z

Hi Shmulik,

Thanks for the review.

On Fri, Nov 23, 2012 at 6:26 PM, Shmulik Ladkani
<shmulik.ladkani@gmail.com> wrote:
[...]
>> - spin_lock(&ubi->wl_lock);
>> - if (list_empty(&ubi->works) || ubi->ro_mode ||
>
> Originally, 'ubi_thread' did nothing if 'ubi->ro_mode'.
> This filtering is missing from 'ubi_wl_do_work' implementation.
> How do we guarantee 'ubi_wl_do_work' is never queued when in RO mode?
>

I believe that we do this through ubi->wq_enabled. See here:

static void __schedule_ubi_work(struct ubi_device *ubi, struct ubi_work *wrk)
{
spin_lock(&ubi->wl_lock);
list_add_tail(&wrk->list, &ubi->works);
ubi_assert(ubi->works_count >= 0);
ubi->works_count += 1;
if (ubi->wq_enabled && !ubi_dbg_is_bgt_disabled(ubi))
queue_work(ubi->workqueue, &ubi->work);
spin_unlock(&ubi->wl_lock);
}

As you can see from above, work is queued only if ubi->wq_enabled
(which should be a boolean and probably with inverse logic,
but that's not important).
Unless I've missed something, this patch doesn't change that.

[...]
>> + if (failures++ > WL_MAX_FAILURES) {
>> + /*
>> + * Too many failures, disable the workqueue and
>> + * switch to read-only mode.
>> + */
>
> This condition will never be met (after your change), since 'failures'
> is local to 'ubi_wl_do_work' (per work invocation).
>
> Formerly, 'failures' was local to 'ubi_thread' (per ubi device's
> thread), hence it was possible that several 'do_works()' calls have
> failed during thread's lifetime, reaching the WL_MAX_FAILURES limit.
>
> If we'd like to preseve the 'failures' semantics, 'failures' should be
> an 'ubi_device' property.
>

Ah, totally right. I overlooked and assumed 'failures' was per-device.
Now I see it's local scoped. Will fix in V2.

> One last thing:
> Some variables and functions (debug and sysfs) are still named *bgt*,
> which is confusing.
>

I made specific reference to that in the commit message.
I didn't want to change any userspace related to prevent
userspace tools/scripts from stop working.

If we all agree (and specially Artem) I can rename everything
to something like wq_foo, wq_bar.

Thanks again!

Ezequiel