linux-kernel - Re: [PATCH] mm: Use special value SHRINKER_REGISTERING instead list

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Date:   Sat, 4 Aug 2018 17:03:05 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, vdavydov.dev@...il.com,
        mhocko@...e.com, aryabinin@...tuozzo.com, ying.huang@...el.com,
        penguin-kernel@...ove.SAKURA.ne.jp, shakeelb@...gle.com,
        jbacik@...com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Use special value SHRINKER_REGISTERING instead
 list_empty() check

On Sat, Aug 04, 2018 at 09:42:05PM +0300, Kirill Tkhai wrote:
> This is exactly the thing the patch makes. Instead of inserting a shrinker pointer
> to idr, it inserts a fake value SHRINKER_REGISTERING there. The patch makes impossible
> to dereference a shrinker unless it's completely registered. 

-       id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
+       id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);

Instead:

+       id = idr_alloc(&shrinker_idr, NULL, 0, 0, GFP_KERNEL);

... and the rest of your patch becomes even simpler.