linux-kernel - Re: [PATCH 01/18] kernel: add bl

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Message-ID: <20101008103352.GD4681@dastard>
Date:	Fri, 8 Oct 2010 21:33:52 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/18] kernel: add bl_list

On Fri, Oct 08, 2010 at 10:18:40AM +0200, Andi Kleen wrote:
> Dave Chinner <david@...morbit.com> writes:
> 
> > +static inline void __hlist_bl_del(struct hlist_bl_node *n)
> > +{
> > +	struct hlist_bl_node *next = n->next;
> > +	struct hlist_bl_node **pprev = n->pprev;
> > +
> > +	LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
> > +
> > +	/* pprev may be `first`, so be careful not to lose the lock bit */
> > +	*pprev = (struct hlist_bl_node *)
> > +			((unsigned long)next |
> > +			 ((unsigned long)*pprev & LIST_BL_LOCKMASK));
> > +	if (next)
> > +		next->pprev = pprev;
> > +}
> 
> Should this set n->pprev to NULL so that unhashed returns true
> afterwards?

No, I think the callers set that appropriately.

> > +
> > +static inline void hlist_bl_del(struct hlist_bl_node *n)
> > +{
> > +	__hlist_bl_del(n);
> > +	n->next = BL_LIST_POISON1;
> > +	n->pprev = BL_LIST_POISON2;
> > +}
> 
> Ok so unhashed only works once. Seems unsymmetric.

Exactly the same behaviour as hlist_del(). If you want
hlist_bl_unhashed() to work, you need to call hlist_bl_del_init().

/me makes a note to check all the inode hash code uses hlist_bl_del_init()
as there are unhashed checks in many places.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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