linux-kernel - Re: [RFC] slab: introduce auto

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Message-ID: <Z-7G6_jm4SKtSO7a@casper.infradead.org>
Date: Thu, 3 Apr 2025 18:35:39 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Kees Cook <kees@...nel.org>
Cc: Vlastimil Babka <vbabka@...e.cz>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	torvalds@...ux-foundation.org, peterz@...radead.org,
	Jann Horn <jannh@...gle.com>, andriy.shevchenko@...ux.intel.com,
	intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
	Harry Yoo <harry.yoo@...cle.com>, Christoph Lameter <cl@...two.org>
Subject: Re: [RFC] slab: introduce auto_kfree macro

On Thu, Apr 03, 2025 at 09:59:41AM -0700, Kees Cook wrote:
> On Wed, Apr 02, 2025 at 12:44:50PM +0200, Vlastimil Babka wrote:
> > Cc Kees and others from his related efforts:
> > 
> > https://lore.kernel.org/all/20250321202620.work.175-kees@kernel.org/
> 
> I think, unfortunately, the consensus is that "invisible side-effects"
> are not going to be tolerated. After I finish with kmalloc_obj(), I'd
> like to take another run at this for basically providing something like:
> 
> static inline __must_check
> void *kfree(void *p) { __kfree(p); return NULL; }
> 
> And then switch all:
> 
> 	kfree(s->ptr);
> 
> to
> 
> 	s->ptr = kfree(s->ptr);
> 
> Where s->ptr isn't used again.

Umm ... kfree is now going to be __must_check?  That's a lot of churn.

I'd just go with making kfree() return NULL and leave off the
__must_check.  It doesn't need the __kfree() indirection either.
That lets individual functions opt into the new safety.