From 0abb964aae3da746ea2fd4301599a6fa26da58db Mon Sep 17 00:00:00 2001 From: Liam Howlett Date: Mon, 19 Dec 2022 16:20:15 +0000 Subject: [PATCH] maple_tree: fix mas_spanning_rebalance() on insufficient data 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 Reported-by: Mike Rapoport Tested-by: Mike Rapoport Cc: Andrei Vagin Cc: Mike Rapoport Cc: Muhammad Usama Anjum Cc: Signed-off-by: Andrew Morton --- lib/maple_tree.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/lib/maple_tree.c b/lib/maple_tree.c index fe3947b80069..26e2045d3cda 100644 --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -2994,7 +2994,9 @@ static int mas_spanning_rebalance(struct ma_state *mas, 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);