linux-kernel - Re: [PATCH 1/2] mm/zsmalloc: don't hold locks of all pages when free

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Message-ID: <20240228043358.GF11972@google.com>
Date: Wed, 28 Feb 2024 13:33:58 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Chengming Zhou <zhouchengming@...edance.com>
Cc: yosryahmed@...gle.com, Sergey Senozhatsky <senozhatsky@...omium.org>,
	hannes@...xchg.org, nphamcs@...il.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 1/2] mm/zsmalloc: don't hold locks of all pages when
 free_zspage()

On (24/02/27 03:02), Chengming Zhou wrote:
[..]
> @@ -978,10 +974,11 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
>  		pages[i] = page;
>  	}
>  
> -	create_page_chain(class, zspage, pages);
>  	init_zspage(class, zspage);
>  	zspage->pool = pool;
>  	zspage->class = class->index;
> +	/* RCU set_zspage() after zspage initialized. */
> +	create_page_chain(class, zspage, pages);

So this hasn't been tested, has it?

init_zspage() does not like to be invoked before create_page_chain(),
because we haven't setup required pointers yet.

So when init_zspage() calls get_first_page() it gets NULL zspage->first_page
which we then use in is_first_page(first_page)->PagePrivate(page). As far as
I can tell.