Re: [PATCH 1/3] list_bl: Add hlist_bl_add_before/behind helpers

From: Mike Snitzer <snitzer@redhat.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	hch@infradead.org, Nikos Tsironis <ntsironis@arrikto.com>
Cc: agk@redhat.com, dm-devel@redhat.com, mpatocka@redhat.com,
	iliastsi@arrikto.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] list_bl: Add hlist_bl_add_before/behind helpers
Date: Thu, 28 Feb 2019 16:34:48 -0500	[thread overview]
Message-ID: <20190228213448.GG23527@redhat.com> (raw)
In-Reply-To: <20190228213201.GB23527@redhat.com>

On Thu, Feb 28 2019 at  4:32pm -0500,
Mike Snitzer <snitzer@redhat.com> wrote:

> On Thu, Dec 20 2018 at  1:06pm -0500,
> Nikos Tsironis <ntsironis@arrikto.com> wrote:
> 
> > Add hlist_bl_add_before/behind helpers to add an element before/after an
> > existing element in a bl_list.
> > 
> > Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
> > Signed-off-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
> > ---
> >  include/linux/list_bl.h | 27 +++++++++++++++++++++++++++
> >  1 file changed, 27 insertions(+)
> > 
> > diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
> > index 3fc2cc57ba1b..2fd918e5fd48 100644
> > --- a/include/linux/list_bl.h
> > +++ b/include/linux/list_bl.h
> > @@ -86,6 +86,33 @@ static inline void hlist_bl_add_head(struct hlist_bl_node *n,
> >  	hlist_bl_set_first(h, n);
> >  }
> >  
> > +static inline void hlist_bl_add_before(struct hlist_bl_node *n,
> > +				       struct hlist_bl_node *next)
> > +{
> > +	struct hlist_bl_node **pprev = next->pprev;
> > +
> > +	n->pprev = pprev;
> > +	n->next = next;
> > +	next->pprev = &n->next;
> > +
> > +	/* pprev may be `first`, so be careful not to lose the lock bit */
> > +	WRITE_ONCE(*pprev,
> > +		   (struct hlist_bl_node *)
> > +			((unsigned long)n |
> > +			 ((unsigned long)*pprev & LIST_BL_LOCKMASK)));
> > +}
> > +
> > +static inline void hlist_bl_add_behind(struct hlist_bl_node *n,
> > +				       struct hlist_bl_node *prev)
> > +{
> > +	n->next = prev->next;
> > +	n->pprev = &prev->next;
> > +	WRITE_ONCE(prev->next, n);
> > +
> > +	if (n->next)
> > +		n->next->pprev = &n->next;
> > +}
> > +
> >  static inline void __hlist_bl_del(struct hlist_bl_node *n)
> >  {
> >  	struct hlist_bl_node *next = n->next;
> > -- 
> > 2.11.0
> 
> Hi Paul and Christoph,
> 
> You've added your Signed-off-by to include/linux/list_bl.h commits in
> the past.  I'm not sure how this proposed patch should be handled.
> 
> These new hlist_bl_add_{before,behind} changes are a prereq for
> dm-snapshot changes that Nikos has proposed, please see:
> https://patchwork.kernel.org/patch/10739265/
> 
> Any assistance/review you, or others on LKML, might be able to provide
> would be appreciated.

I should've clarified that: I'm asking for the purpose of getting these
changes staged for Linux 5.2.

Mike