Re: [PATCH] zsmalloc: Fix races between modifications of fullness and isolated

From: Sergey Senozhatsky <senozhatsky@chromium.org>
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
Subject: Re: [PATCH] zsmalloc: Fix races between modifications of fullness and isolated
Date: Wed, 26 Jul 2023 12:18:46 +0900	[thread overview]
Message-ID: <20230726031846.GJ955071@google.com> (raw)
In-Reply-To: <20230721063705.11455-1-andrew.yang@mediatek.com>

On (23/07/21 14:37), Andrew Yang 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")

Have you observed issues in real life? That commit is more than a year
and a half old, so I wonder.

> @@ -1858,8 +1860,8 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
>  	 * Since we complete the data copy and set up new zspage structure,
>  	 * it's okay to release the pool's lock.
>  	 */

This comment should be moved too, because this is not where we unlock the
pool anymore.

> -	spin_unlock(&pool->lock);
>  	dec_zspage_isolation(zspage);
> +	spin_unlock(&pool->lock);
>  	migrate_write_unlock(zspage);