linux-kernel - Re: UBI fastmap updates

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Date:	Mon, 9 Jul 2012 10:37:47 +0300
From:	Shmulik Ladkani <shmulik.ladkani@...il.com>
To:	Richard Weinberger <richard@....at>
Cc:	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	adrian.hunter@...el.com, Heinz.Egger@...utronix.de,
	thomas.wucher@...utronix.de, tglx@...utronix.de,
	tim.bird@...sony.com, Marius.Mazarel@...l.ro,
	artem.bityutskiy@...ux.intel.com, nyoushchenko@...sta.com
Subject: Re: UBI fastmap updates

Hi Richard,

On Sun, 08 Jul 2012 14:07:41 +0200 Richard Weinberger <richard@....at> wrote:
> > +			/* TODO: in the new locking scheme, produce_free_peb is
> > +			 * called under wl_lock taken.
> > +			 * so when returning, should reacquire the lock
> > +			 */
> 
> Which new locking scheme?

I am diffing linux-ubi fastmap HEAD against its fork point (vanilla
ubi), that's 6b16351..d41a140 on linux-ubi.

Which gives the following diff in produce_free_pebs:

@@ -261,7 +266,6 @@ static int produce_free_peb(struct ubi_device *ubi)
 {
 	int err;
 
-	spin_lock(&ubi->wl_lock);
 	while (!ubi->free.rb_node) {
 		spin_unlock(&ubi->wl_lock);
 
@@ -272,7 +276,6 @@ static int produce_free_peb(struct ubi_device *ubi)
 
 		spin_lock(&ubi->wl_lock);
 	}
-	spin_unlock(&ubi->wl_lock);
 
 	return 0;
 }

Which is probably okay, since you obtain the lock in the new
'ubi_refill_pools', which calls produce_free_peb:

+void ubi_refill_pools(struct ubi_device *ubi)
+{
+	spin_lock(&ubi->wl_lock);
+	refill_wl_pool(ubi);
+	refill_wl_user_pool(ubi);
+	spin_unlock(&ubi->wl_lock);
+}

However if 'do_work' fails within 'produce_free_peb', you return the
error but leave wl_lock unlocked - where it is expected to be locked
(otherwise, ubi_refill_pools will unlock it again):

static int produce_free_peb(struct ubi_device *ubi)
{
	int err;

	while (!ubi->free.rb_node) {
		spin_unlock(&ubi->wl_lock);

		dbg_wl("do one work synchronously");
		err = do_work(ubi);
		if (err)
			return err;

		spin_lock(&ubi->wl_lock);
	}

	return 0;
}

Regards,
Shmulik
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