On Fri 20-08-10 15:22:06, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> Commit f446daaea9d4a420d16c606f755f3689dcb2d0ce ("mm: implement
> writeback livelock avoidance using page tagging") introduced a new
> radix tree tag, increasing the number of tags in each node from 2 to
> 3. It did not, however, fix up the code in
> radix_tree_node_rcu_free() that cleans up after radix_tree_shrink()
> and hence could leave stray tags set in the new tag array.
>
> The result is that the livelock avoidance code added in the the
> above commit would hit stale tags when doing tag based lookups,
> resulting in livelocks when trying to traverse the tree.
>
> Fix this problem in radix_tree_node_rcu_free() so it doesn't happen
> again in the future by using a loop to walk all the tags up to
> RADIX_TREE_MAX_TAGS to clear the stray tags radix_tree_shrink()
> leaves behind.
The patch looks good. Thanks!
Acked-by: Jan Kara <jack@xxxxxxx>
Honza
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> lib/radix-tree.c | 6 ++++--
> 1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/lib/radix-tree.c b/lib/radix-tree.c
> index e907858..1014171 100644
> --- a/lib/radix-tree.c
> +++ b/lib/radix-tree.c
> @@ -174,14 +174,16 @@ static void radix_tree_node_rcu_free(struct rcu_head *head)
> {
> struct radix_tree_node *node =
> container_of(head, struct radix_tree_node, rcu_head);
> + int i;
>
> /*
> * must only free zeroed nodes into the slab. radix_tree_shrink
> * can leave us with a non-NULL entry in the first slot, so clear
> * that here to make sure.
> */
> - tag_clear(node, 0, 0);
> - tag_clear(node, 1, 0);
> + for (i = 0; i < RADIX_TREE_MAX_TAGS; i++)
> + tag_clear(node, i, 0);
> +
> node->slots[0] = NULL;
> node->count = 0;
>
> --
> 1.7.1
>
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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