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References: <20220605145835.26916-1-wuchi.zero@gmail.com>
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From:   chi wu <wuchi.zero@gmail.com>
Date:   Fri, 17 Jun 2022 18:08:45 +0800
Message-ID: <CA+tQmHAkkxFkuabjh1Apwp1ZkNEtY+7ijLEs931aFA+MZngECA@mail.gmail.com>
Subject: Re: [PATCH] lib/sbitmap: Fix invalid loop in __sbitmap_queue_get_batch()
To:     axboe@kernel.dk, mwilck@suse.com, andriy.shevchenko@linux.intel.com
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
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wuchi <wuchi.zero@gmail.com> =E4=BA=8E2022=E5=B9=B46=E6=9C=885=E6=97=A5=E5=
=91=A8=E6=97=A5 22:58=E5=86=99=E9=81=93=EF=BC=9A
>
> 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@gmail.com>
> ---
>  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 sbitma=
p_queue *sbq, int nr_tags,
>
>                 sbitmap_deferred_clear(map);
>                 if (map->word =3D=3D (1UL << (map_depth - 1)) - 1)
> -                       continue;
> +                       goto next;
>
>                 nr =3D find_first_zero_bit(&map->word, map_depth);
>                 if (nr + nr_tags <=3D map_depth) {
> @@ -539,6 +539,8 @@ unsigned long __sbitmap_queue_get_batch(struct sbitma=
p_queue *sbq, int nr_tags,
>                         get_mask =3D ((1UL << map_tags) - 1) << nr;
>                         do {
>                                 val =3D READ_ONCE(map->word);
> +                               if ((val & ~get_mask) !=3D val)
> +                                       goto next;
>                                 ret =3D atomic_long_cmpxchg(ptr, val, get=
_mask | val);
>                         } while (ret !=3D val);
>                         get_mask =3D (get_mask & ~ret) >> nr;
> @@ -549,6 +551,7 @@ unsigned long __sbitmap_queue_get_batch(struct sbitma=
p_queue *sbq, int nr_tags,
>                                 return get_mask;
>                         }
>                 }
> +next:
>                 /* Jump to next index. */
>                 if (++index >=3D sb->map_nr)
>                         index =3D 0;
> --
> 2.20.1
>