Re: [PATCH v2 1/2] mm,vmscan: Make unregister_shrinker() no-op if register_shrinker() failed.

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Michal Hocko wrote:
> On Fri 24-11-17 22:21:55, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > > Since we can encourage register_shrinker() callers to check for failure
> > > > by marking register_shrinker() as __must_check, unregister_shrinker()
> > > > can stay silent.
> > > 
> > > I am not sure __must_check is the right way. We already do get
> > > allocation warning if the registration fails so silent unregister is
> > > acceptable. Unchecked register_shrinker is a bug like any other
> > > unchecked error path.
> > 
> > I consider that __must_check is the simplest way to find all of
> > unchecked register_shrinker bugs. Why not to encourage users to fix?
> 
> because git grep doesn't require to patch the kernel and still provide
> the information you want.

I can't interpret this line. How git grep relevant?

If all register_shrinker() users were careful enough to check for git history
everytime, we would not have come to current code. It is duty of patch author
to take necessary precautions (for in-tree code) when some API starts to
return an error which previously did not return an error. In this case, it is
duty of author of commit 1d3d4437eae1bb29 ("vmscan: per-node deferred work").

>                           I would understand __must_check if we had
> hundreds users of this api and they come and go quickly.

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