+ maple_tree-fix-mas_spanning_rebalance-on-insufficient-data.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: maple_tree: fix mas_spanning_rebalance() on insufficient data
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     maple_tree-fix-mas_spanning_rebalance-on-insufficient-data.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/maple_tree-fix-mas_spanning_rebalance-on-insufficient-data.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Liam Howlett <liam.howlett@oracle.com>
Subject: maple_tree: fix mas_spanning_rebalance() on insufficient data
Date: Mon, 19 Dec 2022 16:20:15 +0000

Mike Rapoport contacted me off-list with a regression in running criu. 
Periodic tests fail with an RCU stall during execution.  Although rare, it
is possible to hit this with other uses so this patch should be backported
to fix the regression.

This patchset adds the fix and a test case to the maple tree test
suite.


This patch (of 2):

An insufficient node was causing an out-of-bounds access on the node in
mas_leaf_max_gap().  The cause was the faulty detection of the new node
being a root node when overwriting many entries at the end of the tree.

Fix the detection of a new root and ensure there is sufficient data prior
to entering the spanning rebalance loop.

Link: https://lkml.kernel.org/r/20221219161922.2708732-1-Liam.Howlett@oracle.com
Link: https://lkml.kernel.org/r/20221219161922.2708732-2-Liam.Howlett@oracle.com
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reported-by: Mike Rapoport <rppt@kernel.org>
Tested-by: Mike Rapoport <rppt@kernel.org>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/maple_tree.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/lib/maple_tree.c~maple_tree-fix-mas_spanning_rebalance-on-insufficient-data
+++ a/lib/maple_tree.c
@@ -2994,7 +2994,9 @@ static int mas_spanning_rebalance(struct
 	mast->free = &free;
 	mast->destroy = &destroy;
 	l_mas.node = r_mas.node = m_mas.node = MAS_NONE;
-	if (!(mast->orig_l->min && mast->orig_r->max == ULONG_MAX) &&
+
+	/* Check if this is not root and has sufficient data.  */
+	if (((mast->orig_l->min != 0) || (mast->orig_r->max != ULONG_MAX)) &&
 	    unlikely(mast->bn->b_end <= mt_min_slots[mast->bn->type]))
 		mast_spanning_rebalance(mast);
 
_

Patches currently in -mm which might be from liam.howlett@oracle.com are

maple_tree-fix-mas_spanning_rebalance-on-insufficient-data.patch
test_maple_tree-add-test-for-mas_spanning_rebalance-on-insufficient-data.patch