Re: [PATCH v8 14/21] mm/mmap: Avoid zeroing vma tree in mmap_region()

Lorenzo Stoakes
2024-10-04T14:23:51Z

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.

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@oracle.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