linux-kernel - Re: [RFC] mm/shrinker: define INIT

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Message-Id: <20150710183357.30605207.akpm@linux-foundation.org>
Date:	Fri, 10 Jul 2015 18:33:57 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] mm/shrinker: define INIT_SHRINKER macro

On Sat, 11 Jul 2015 10:25:13 +0900 Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:

> > > I was thinking of a trivial INIT_SHRINKER macro to init `struct shrinker'
> > > internal members (composed in email client, not tested)
> > > 
> > > include/linux/shrinker.h
> > > 
> > > #define INIT_SHRINKER(s)			\
> > > 	do {					\
> > > 		(s)->nr_deferred = NULL;	\
> > > 		INIT_LIST_HEAD(&(s)->list);	\
> > > 	} while (0)
> > 
> > Spose so.  Although it would be simpler to change unregister_shrinker()
> > to bale out if list.next==NULL and then say "all zeroes is the
> > initialized state".
> 
> Yes, or '->nr_deferred == NULL' -- we can't have NULL ->nr_deferred
> in a properly registered shrinker (as of now)

list.next seems safer because that will always be non-zero.  But
whatever - we can change it later.
 
> But that will not work if someone has accidentally passed not zeroed
> out pointer to unregister.

I wouldn't worry about that really.  If you pass a pointer to
uninitialized memory, the kernel will explode.  That's true of just
about every pointer-accepting function in the kernel.


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