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    Subject[PATCH 18/30] radix-tree: Fix multiorder BUG_ON in radix_tree_insert
    Date
    These BUG_ON tests are to ensure that all the tags are clear when
    inserting a new entry. If we insert a multiorder entry, we'll end up
    looking at the tags for a different node, and so the BUG_ON can end up
    triggering spuriously.

    Also, we now have three tags, not two, so check all three are clear,
    and check all the root tags with a single call to BUG_ON since the bits
    are stored contiguously.

    Include a test-case to ensure this problem does not reoccur.

    Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
    Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
    ---
    lib/radix-tree.c | 16 ++++++++++++----
    tools/testing/radix-tree/multiorder.c | 13 +++++++++++++
    2 files changed, 25 insertions(+), 4 deletions(-)

    diff --git a/lib/radix-tree.c b/lib/radix-tree.c
    index 2ca2b416b476..33f91f207587 100644
    --- a/lib/radix-tree.c
    +++ b/lib/radix-tree.c
    @@ -165,6 +165,11 @@ static inline int root_tag_get(struct radix_tree_root *root, unsigned int tag)
    return (__force unsigned)root->gfp_mask & (1 << (tag + __GFP_BITS_SHIFT));
    }

    +static inline unsigned root_tags_get(struct radix_tree_root *root)
    +{
    + return (__force unsigned)root->gfp_mask >> __GFP_BITS_SHIFT;
    +}
    +
    /*
    * Returns 1 if any slot in the node has this tag set.
    * Otherwise returns 0.
    @@ -604,12 +609,15 @@ int __radix_tree_insert(struct radix_tree_root *root, unsigned long index,
    rcu_assign_pointer(*slot, item);

    if (node) {
    + unsigned shift = ((node->path - 1) & RADIX_TREE_HEIGHT_MASK) *
    + RADIX_TREE_MAP_SHIFT;
    + unsigned offset = (index >> shift) & RADIX_TREE_MAP_MASK;
    node->count++;
    - BUG_ON(tag_get(node, 0, index & RADIX_TREE_MAP_MASK));
    - BUG_ON(tag_get(node, 1, index & RADIX_TREE_MAP_MASK));
    + BUG_ON(tag_get(node, 0, offset));
    + BUG_ON(tag_get(node, 1, offset));
    + BUG_ON(tag_get(node, 2, offset));
    } else {
    - BUG_ON(root_tag_get(root, 0));
    - BUG_ON(root_tag_get(root, 1));
    + BUG_ON(root_tags_get(root));
    }

    return 0;
    diff --git a/tools/testing/radix-tree/multiorder.c b/tools/testing/radix-tree/multiorder.c
    index cfe718c78eb6..606bfe04b104 100644
    --- a/tools/testing/radix-tree/multiorder.c
    +++ b/tools/testing/radix-tree/multiorder.c
    @@ -46,6 +46,17 @@ static void multiorder_check(unsigned long index, int order)
    item_check_absent(&tree, i);
    }

    +static void multiorder_insert_bug(void)
    +{
    + RADIX_TREE(tree, GFP_KERNEL);
    +
    + item_insert(&tree, 0);
    + radix_tree_tag_set(&tree, 0, 0);
    + item_insert_order(&tree, 3 << 6, 6);
    +
    + item_kill_tree(&tree);
    +}
    +
    void multiorder_checks(void)
    {
    int i;
    @@ -55,4 +66,6 @@ void multiorder_checks(void)
    multiorder_check(0, i);
    multiorder_check((1UL << i) + 1, i);
    }
    +
    + multiorder_insert_bug();
    }
    --
    2.8.0.rc3
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