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References: <20230727062910.6337-1-andrew.yang@mediatek.com>
In-Reply-To: <20230727062910.6337-1-andrew.yang@mediatek.com>
From:   Nhat Pham <nphamcs@gmail.com>
Date:   Thu, 10 Aug 2023 08:37:21 -0700
Message-ID: <CAKEwX=ObJO8R6ybwXS0iDd0Vrb_pUqJpAV9oV68hsJr2aMsRoA@mail.gmail.com>
Subject: Re: [PATCH v2] zsmalloc: Fix races between modifications of fullness
 and isolated
To:     Andrew Yang <andrew.yang@mediatek.com>
Cc:     Minchan Kim <minchan@kernel.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        wsd_upstream@mediatek.com, casper.li@mediatek.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org
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On Wed, Jul 26, 2023 at 11:30=E2=80=AFPM Andrew Yang <andrew.yang@mediatek.=
com> wrote:
>
> Since fullness and isolated share the same unsigned int,
> modifications of them should be protected by the same lock.
>
> Signed-off-by: Andrew Yang <andrew.yang@mediatek.com>
> Fixes: c4549b871102 ("zsmalloc: remove zspage isolation for migration")
> ---
> v2: Moving comment too
> ---
>  mm/zsmalloc.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 32f5bc4074df..b58f957429f0 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1777,6 +1777,7 @@ static void replace_sub_page(struct size_class *cla=
ss, struct zspage *zspage,
>
>  static bool zs_page_isolate(struct page *page, isolate_mode_t mode)
>  {
> +       struct zs_pool *pool;
>         struct zspage *zspage;
>
>         /*
> @@ -1786,9 +1787,10 @@ static bool zs_page_isolate(struct page *page, iso=
late_mode_t mode)
>         VM_BUG_ON_PAGE(PageIsolated(page), page);
>
>         zspage =3D get_zspage(page);
> -       migrate_write_lock(zspage);
> +       pool =3D zspage->pool;
> +       spin_lock(&pool->lock);
>         inc_zspage_isolation(zspage);
> -       migrate_write_unlock(zspage);
> +       spin_unlock(&pool->lock);
>
>         return true;
>  }
> @@ -1854,12 +1856,12 @@ static int zs_page_migrate(struct page *newpage, =
struct page *page,
>         kunmap_atomic(s_addr);
>
>         replace_sub_page(class, zspage, newpage, page);
> +       dec_zspage_isolation(zspage);
>         /*
>          * Since we complete the data copy and set up new zspage structur=
e,
>          * it's okay to release the pool's lock.
>          */
>         spin_unlock(&pool->lock);
> -       dec_zspage_isolation(zspage);
>         migrate_write_unlock(zspage);
>
>         get_page(newpage);
> @@ -1876,14 +1878,16 @@ static int zs_page_migrate(struct page *newpage, =
struct page *page,
>
>  static void zs_page_putback(struct page *page)
>  {
> +       struct zs_pool *pool;
>         struct zspage *zspage;
>
>         VM_BUG_ON_PAGE(!PageIsolated(page), page);
>
>         zspage =3D get_zspage(page);
> -       migrate_write_lock(zspage);
> +       pool =3D zspage->pool;
> +       spin_lock(&pool->lock);
>         dec_zspage_isolation(zspage);
> -       migrate_write_unlock(zspage);
> +       spin_unlock(&pool->lock);
>  }
>
>  static const struct movable_operations zsmalloc_mops =3D {
> --
> 2.18.0
>
>

I think this fixes an issue of mine that has been bugging me for
the past couple of weeks :) Thanks a lot, Andrew!

This should be added to other Linux stable versions too, right?
(with the caveat that before 6.2, use class's lock instead of
pool's lock).

Reviewed-by: Nhat Pham <nphamcs@gmail.com>