From: Liam Howlett <liam.howlett@xxxxxxxxxx> commit 0abb964aae3da746ea2fd4301599a6fa26da58db upstream. 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@xxxxxxxxxx Link: https://lkml.kernel.org/r/20221219161922.2708732-2-Liam.Howlett@xxxxxxxxxx Fixes: 54a611b60590 ("Maple Tree: add new data structure") Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> Reported-by: Mike Rapoport <rppt@xxxxxxxxxx> Tested-by: Mike Rapoport <rppt@xxxxxxxxxx> Cc: Andrei Vagin <avagin@xxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxx> Cc: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- lib/maple_tree.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -2989,7 +2989,9 @@ 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);
