Re: [PATCH v3 21/30] maple_tree: Add cp_is_new_root() helper

[SeongJae Park <sj@kernel.org>]

On Mon, 2 Feb 2026 09:58:31 -0500 "Liam R. Howlett" <Liam.Howlett@oracle.com> wrote:

> * SeongJae Park <sj@kernel.org> [260131 19:10]:
> > Hello,
> > 
> > On Fri, 30 Jan 2026 15:59:26 -0500 "Liam R. Howlett" <Liam.Howlett@oracle.com> wrote:
> > 
> > > Add a helper to do what is needed when the maple copy node contains a
> > > new root node.  This is useful for future commits and is
> > > self-documenting code.
> > > 
> > > Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> > > ---
> > >  lib/maple_tree.c | 70 ++++++++++++++++++++++++++----------------------
> > >  1 file changed, 38 insertions(+), 32 deletions(-)
> > > 
> > > diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> > > index 5280fa6d2d6ec..42038e42a4c7e 100644
> > > --- a/lib/maple_tree.c
> > > +++ b/lib/maple_tree.c
> > > @@ -3337,6 +3337,43 @@ static void mas_spanning_rebalance(struct ma_state *mas,
> > >  	mas_spanning_rebalance_loop(mas, mast, count);
> > >  }
> > >  
> > > +static inline bool cp_is_new_root(struct maple_copy *cp, struct ma_state *mas)
> > > +{
> > > +	if (cp->min || cp->max != ULONG_MAX)
> > > +		return false;
> > > +
> > > +	if (cp->d_count != 1) {
> > > +		enum maple_type mt = maple_arange_64;
> > > +
> > > +		if (!mt_is_alloc(mas->tree))
> > > +			mt = maple_range_64;
> > > +
> > > +		cp->data = cp->d_count;
> > > +		cp->s_count = 0;
> > > +		dst_setup(cp, mas, mt);
> > > +		init_cp_src(cp);
> > > +		node_copy(mas, cp->src[0].node, 0, cp->data, cp->max, maple_copy,
> > > +			  cp->dst[0].node, 0, mt);
> > > +		node_finalise(cp->dst[0].node, mt, cp->end + 1);
> > > +		/*
> > > +		 * Warning, see cp_leaf_init() comment and rcu_assign_pointer()
> > > +		 * documentation.  Since this is a new root, there are no
> > > +		 * read-side operations that can view it until it is insert into
> > > +		 * the tree after an rcu_assign_pointer() call.
> > > +		 */
> > > +		RCU_INIT_POINTER(cp->slot[0], mt_mk_node(cp->dst[0].node, mt));
> > 
> > I just found the above makes my build test using an old version compiler fails.
> > Fortunately, seems it is same to the one we discussed before [1], and same
> > mitigation like below attached patch works, at least for my test setup.
> 
> Thanks SJ.

My pleasure :)

> 
> This is still with gcc 8.1.0?

Yes.  The test code is available at GitHub [1].

Nonetheless, another test [2] that is using 9.3.0 was also failing.


[1] https://github.com/damonitor/damon-tests/blob/master/corr/tests/build_m68k.sh
[2] https://github.com/damonitor/damon-tests/blob/master/corr/tests/build_arm64.sh


Thanks,
SJ

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