linux-kernel - Re: [PATCH v7 1/6] zswap: fix writeback lock ordering for zsmalloc

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Message-ID: <Y4WA5DQMjXrjC8uO@google.com>
Date:   Tue, 29 Nov 2022 12:47:48 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Nhat Pham <nphamcs@...il.com>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, minchan@...nel.org,
        ngupta@...are.org, senozhatsky@...omium.org, sjenning@...hat.com,
        ddstreet@...e.org, vitaly.wool@...sulko.com
Subject: Re: [PATCH v7 1/6] zswap: fix writeback lock ordering for zsmalloc

On (22/11/28 11:16), Nhat Pham wrote:
> zswap's customary lock order is tree->lock before pool->lock, because
> the tree->lock protects the entries' refcount, and the free callbacks in
> the backends acquire their respective pool locks to dispatch the backing
> object. zsmalloc's map callback takes the pool lock, so zswap must not
> grab the tree->lock while a handle is mapped. This currently only
> happens during writeback, which isn't implemented for zsmalloc. In
> preparation for it, move the tree->lock section out of the mapped entry
> section
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Nhat Pham <nphamcs@...il.com>

Reviewed-by: Sergey Senozhatsky <senozhatsky@...omium.org>