linux-kernel - Re: [PATCH v8 14/21] mm/mmap: Avoid zeroing vma tree in mmap

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Message-ID: <2394412b-3037-4867-b16e-f155740d062c@lucifer.local>
Date: Sat, 5 Oct 2024 12:11:35 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Bert Karwatzki <spasswolf@....de>
Cc: "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 14/21] mm/mmap: Avoid zeroing vma tree in mmap_region()

On Sat, Oct 05, 2024 at 10:57:59AM +0200, Bert Karwatzki wrote:
>
> > >
> > > I just tested this and it passed ten tests (i.e. upgrading the proton version i
> > > steam) in a row.
> > >
> > > Bert Karwatzki
> >
> > Perfect :) will send the fix upstream then as a hotfix for 6.12! Thanks
> > very much for helping out with this, your help has been absolutely
> > invaluable and HUGELY appreciated.
> >
> > Cheers, Lorenzo
>
> I also tried another debugging patch:
>
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index e6f0da908ba7..35b0fe3e02f7 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -3773,6 +3773,8 @@ static noinline void mas_wr_spanning_store(struct
> ma_wr_state *wr_mas)
>         /* Copy l_mas and store the value in b_node. */
>         mas_store_b_node(&l_wr_mas, &b_node, l_mas.end);
>         /* Copy r_mas into b_node. */
> +       if (!r_populated && r_mas.offset <= r_mas.end)
> +               printk(KERN_INFO "%s: avoiding maple tree corrution\n",
> __func__);
>         if (r_populated && r_mas.offset <= r_mas.end)
>                 mas_mab_cp(&r_mas, r_mas.offset, r_mas.end,
>                            &b_node, b_node.b_end + 1);
>
> and when running the test this prints
>
> [  293.477904] [   T5720] mas_wr_spanning_store: avoiding maple tree corrution
> [  293.480202] [   T5720] mas_wr_spanning_store: avoiding maple tree corrution
> [  293.482087] [   T5720] mas_wr_spanning_store: avoiding maple tree corrution
> [  293.484786] [   T5720] mas_wr_spanning_store: avoiding maple tree corrution
> [  293.486644] [   T5720] mas_wr_spanning_store: avoiding maple tree corrution

Thanks, interesting it occurred repeatedly...

I suspect there are situations in which this kind of corruption can occur and
not be a problem too. Nasty one all round!

>
> in dmesg.
>
> Bert Karwatzki