linux-kernel - Re: [PATCH v2 32/36] maple_tree: Clear up index and last setting in single entry tree

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Date:   Fri, 12 May 2023 13:29:23 -0400
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Peng Zhang <zhangpeng.00@...edance.com>,
        maple-tree@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 32/36] maple_tree: Clear up index and last setting in
 single entry tree

* Liam R. Howlett <Liam.Howlett@...cle.com> [230512 11:54]:
> * Peng Zhang <zhangpeng.00@...edance.com> [230509 08:39]:
> > 
> > 
> > 在 2023/5/6 01:42, Liam R. Howlett 写道:
> > > 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 user
> > > walks.  Ensure the correct node setting as well; either MAS_ROOT or
> > > MAS_NONE.
> > > 
> > > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > > ---
> > >   lib/maple_tree.c | 21 +++++++++++----------
> > >   1 file changed, 11 insertions(+), 10 deletions(-)
> > > 
> > > 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 = MAS_START;
> > 
> > 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).
> > 
> > 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().
> 
> 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.


> 
> > 
> > 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: Assertion
> > `0' failed.
> > Aborted (core dumped)
> > >   retry:
> > >   	entry = 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 = 0;
> > > +		mas->last = ULONG_MAX;
> > > +	} else if (mas_is_ptr(mas)) {
> > >   		if (!mas->index) {
> > >   			mas->last = 0;
> > > -		} else {
> > > -			mas->index = 1;
> > > -			mas->last = ULONG_MAX;
> > > +			return entry;
> > >   		}
> > > -		return entry;
> > > -	}
> > > -	if (mas_is_none(mas)) {
> > > -		mas->index = 0;
> > > +		mas->index = 1;
> > >   		mas->last = ULONG_MAX;
> > > +		mas->node = MAS_NONE;
> > > +		return NULL;
> > >   	}
> > >   	return entry;