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Date:   Fri, 12 May 2023 13:29:23 -0400
From:   "Liam R. Howlett" <Liam.Howlett@Oracle.com>
To:     Peng Zhang <zhangpeng.00@bytedance.com>,
        maple-tree@lists.infradead.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v2 32/36] maple_tree: Clear up index and last setting in
 single entry tree
Message-ID: <20230512172923.eqiq34bcotbcro6b@revolver>
Mail-Followup-To: "Liam R. Howlett" <Liam.Howlett@Oracle.com>,
        Peng Zhang <zhangpeng.00@bytedance.com>,
        maple-tree@lists.infradead.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>
References: <20230505174204.2665599-1-Liam.Howlett@oracle.com>
 <20230505174204.2665599-33-Liam.Howlett@oracle.com>
 <5ca5da7f-1b17-b22b-58c4-eae41443e334@bytedance.com>
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* Liam R. Howlett <Liam.Howlett@Oracle.com> [230512 11:54]:
> * Peng Zhang <zhangpeng.00@bytedance.com> [230509 08:39]:
> >=20
> >=20
> > =E5=9C=A8 2023/5/6 01:42, Liam R. Howlett =E5=86=99=E9=81=93:
> > > When there is a single entry tree (range of 0-0 pointing to an entry)=
,
> > > then ensure the limit is either 0-0 or 1-oo, depending on where the u=
ser
> > > walks.  Ensure the correct node setting as well; either MAS_ROOT or
> > > MAS_NONE.
> > >=20
> > > Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> > > ---
> > >   lib/maple_tree.c | 21 +++++++++++----------
> > >   1 file changed, 11 insertions(+), 10 deletions(-)
> > >=20
> > > diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> > > index f060c71965c0d..914399519cf54 100644
> > > --- a/lib/maple_tree.c
> > > +++ b/lib/maple_tree.c
> > > @@ -5022,24 +5022,25 @@ void *mas_walk(struct ma_state *mas)
> > >   {
> > >   	void *entry;
> > > +	if (mas_is_none(mas) || mas_is_paused(mas))
> > if (mas_is_none(mas) || mas_is_paused(mas) || mas_is_ptr(mas))
> > > +		mas->node =3D MAS_START;
> >=20
> > Hi, Liam
> > There is an issue that it cannot pass the user space test program
> > with this patchset.
> > I tested it based on 47cba14ce6fc4(linux-next/master).
> >=20
> > The reason is that mas_walk() does not handle the state that mas is
> > root. The root cause is that mas_start() only handles the start state,
> > and returns NULL for the root state. When encountering the root state,
> > we can reset to start so that it is handled in mas_start().
>=20
> Thanks.  I'll have a look and adjust v3.

This was introduced with the fix for the race condition between v1 and
v2.

It is probably best to reset to MAS_START instead of the potential stale
data.


>=20
> >=20
> > log:
> > BUG at check_state_handling:3076 (1)
> > maple_tree(0x55d6a9838ca0) flags 1, height 0 root 0x1234500
> > 0: 0x1234500
> > Pass: 453406336 Run:453406337
> > maple: ../../../lib/test_maple_tree.c:3076: check_state_handling: Asser=
tion
> > `0' failed.
> > Aborted (core dumped)
> > >   retry:
> > >   	entry =3D mas_state_walk(mas);
> > > -	if (mas_is_start(mas))
> > > +	if (mas_is_start(mas)) {
> > >   		goto retry;
> > > -
> > > -	if (mas_is_ptr(mas)) {
> > > +	} else if (mas_is_none(mas)) {
> > > +		mas->index =3D 0;
> > > +		mas->last =3D ULONG_MAX;
> > > +	} else if (mas_is_ptr(mas)) {
> > >   		if (!mas->index) {
> > >   			mas->last =3D 0;
> > > -		} else {
> > > -			mas->index =3D 1;
> > > -			mas->last =3D ULONG_MAX;
> > > +			return entry;
> > >   		}
> > > -		return entry;
> > > -	}
> > > -	if (mas_is_none(mas)) {
> > > -		mas->index =3D 0;
> > > +		mas->index =3D 1;
> > >   		mas->last =3D ULONG_MAX;
> > > +		mas->node =3D MAS_NONE;
> > > +		return NULL;
> > >   	}
> > >   	return entry;