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 Sat 25-11-17 10:40:13, Tetsuo Handa wrote:
> > 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?
> 
> you do not have to compile to see who is checking the return value.
> Seriously there is no need to overcomplicate this. Newly added shrinkers
> know the function returns might fail so we just have to handle existing
> users and there are not all that many of those.

Newly added shrinker users are not always careful. See commit f2517eb76f1f2f7f
("android: binder: Add global lru shrinker to binder") for example.
Unless we send __must_check change to linux.git, people won't notice it.

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