Re: [PATCH] lib/sbitmap: Fix invalid loop in __sbitmap_queue_get_batch()

[Martin Wilck]

On Sun, 2022-06-05 at 22:58 +0800, wuchi wrote:
> 1. Getting next index before continue branch.
> 2. Checking free bits when setting the target bits. Otherwise,
> it may reuse the busying bits.
> 
> Signed-off-by: wuchi <wuchi.zero@xxxxxxxxx>

Reviewed-by: Martin Wilck <mwilck@xxxxxxxx>

> ---
>  lib/sbitmap.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/sbitmap.c b/lib/sbitmap.c
> index ae4fd4de9ebe..29eb0484215a 100644
> --- a/lib/sbitmap.c
> +++ b/lib/sbitmap.c
> @@ -528,7 +528,7 @@ unsigned long __sbitmap_queue_get_batch(struct
> sbitmap_queue *sbq, int nr_tags,
>  
>                 sbitmap_deferred_clear(map);
>                 if (map->word == (1UL << (map_depth - 1)) - 1)
> -                       continue;
> +                       goto next;
>  
>                 nr = find_first_zero_bit(&map->word, map_depth);
>                 if (nr + nr_tags <= map_depth) {
> @@ -539,6 +539,8 @@ unsigned long __sbitmap_queue_get_batch(struct
> sbitmap_queue *sbq, int nr_tags,
>                         get_mask = ((1UL << map_tags) - 1) << nr;
>                         do {
>                                 val = READ_ONCE(map->word);
> +                               if ((val & ~get_mask) != val)
> +                                       goto next;
>                                 ret = atomic_long_cmpxchg(ptr, val,
> get_mask | val);
>                         } while (ret != val);
>                         get_mask = (get_mask & ~ret) >> nr;
> @@ -549,6 +551,7 @@ unsigned long __sbitmap_queue_get_batch(struct
> sbitmap_queue *sbq, int nr_tags,
>                                 return get_mask;
>                         }
>                 }
> +next:
>                 /* Jump to next index. */
>                 if (++index >= sb->map_nr)
>                         index = 0;