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

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Message-ID: <a34fe509-f1d0-482e-9aa9-8dc3fa0743f3@lucifer.local>
Date: Fri, 4 Oct 2024 15:26:26 +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 Fri, Oct 04, 2024 at 03:23:37PM +0100, Lorenzo Stoakes wrote:
> On Fri, Oct 04, 2024 at 11:35:44AM +0200, Bert Karwatzki wrote:
> > Here's the log procduced by this kernel:
> >
> > c9e7f76815d3 (HEAD -> maple_tree_debug_4) hack: set of info stuff v5
> > 7e3bb072761a mm: correct error handling in mmap_region()
> > 77df9e4bb222 (tag: next-20241001, origin/master, origin/HEAD, master) Add linux-next specific files for 20241001
> >
> > Again it took two attempts to trigger the bug.
> >
> > Bert Karwatzki
> >
>
> Hi Bert, please try the below fix.

OK sorry please abort that, my git tree was screwed up this won't work (ugh).

Let me redo this...

>
> It fails a couple tests in the test suite so this might not be stable but
> it fixes my repro, be good to confirm it fixes the issue for you.
>
> Thanks!
>
> ----8<----
> From 07485683fcd3d8d22996d82bdbde0e3647f2349e Mon Sep 17 00:00:00 2001
> From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Date: Fri, 4 Oct 2024 15:18:58 +0100
> Subject: [PATCH] fix
>
> ---
>  lib/maple_tree.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 37abf0fe380b..fc221a9f23f2 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -3527,6 +3527,7 @@ static bool mas_wr_walk(struct ma_wr_state *wr_mas)
>  	return true;
>  }
>
> +// Return whether the node actually contains entries at or greater than wr_mas->mas->index.
>  static bool mas_wr_walk_index(struct ma_wr_state *wr_mas)
>  {
>  	struct ma_state *mas = wr_mas->mas;
> @@ -3696,6 +3697,7 @@ static noinline void mas_wr_spanning_store(struct ma_wr_state *wr_mas)
>  	struct maple_big_node b_node;
>  	struct ma_state *mas;
>  	unsigned char height;
> +	bool r_populated;
>
>  	/* Left and Right side of spanning store */
>  	MA_STATE(l_mas, NULL, 0, 0);
> @@ -3737,7 +3739,7 @@ static noinline void mas_wr_spanning_store(struct ma_wr_state *wr_mas)
>  		r_mas.last++;
>
>  	r_mas.index = r_mas.last;
> -	mas_wr_walk_index(&r_wr_mas);
> +	r_populated = mas_wr_walk_index(&r_wr_mas);
>  	r_mas.last = r_mas.index = mas->last;
>
>  	/* Set up left side. */
> @@ -3759,9 +3761,12 @@ static noinline void mas_wr_spanning_store(struct ma_wr_state *wr_mas)
>
>  	memset(&b_node, 0, sizeof(struct maple_big_node));
>  	/* 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_mas.offset <= r_mas.end)
> +
> +	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);
>  	else
> --
> 2.46.2