Re: [PATCH] mm: Use special value SHRINKER_REGISTERING instead list_empty() check

[Matthew Wilcox]

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.