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Date: Mon, 01 Jan 2024 10:29:21 -0500
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Markus Elfring <Markus.Elfring@web.de>, 
 Willem de Bruijn <willemdebruijn.kernel@gmail.com>, 
 netdev@vger.kernel.org, 
 kernel-janitors@vger.kernel.org, 
 "David S. Miller" <davem@davemloft.net>, 
 Eric Dumazet <edumazet@google.com>, 
 Jakub Kicinski <kuba@kernel.org>, 
 Paolo Abeni <pabeni@redhat.com>, 
 Stephen Hemminger <stephen@networkplumber.org>
Cc: LKML <linux-kernel@vger.kernel.org>
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Subject: Re: packet: Improve exception handling in fanout_add()
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Markus Elfring wrote:
> > It is fine to call kfree with a possible NULL pointer:
> =E2=80=A6
> > 	 * If @object is NULL, no operation is performed.
> > 	 */
> > 	void kfree(const void *object)
> =

> Such a function call triggers an input parameter validation
> with a corresponding immediate return, doesn't it?
> Do you find such data processing really helpful for the desired error/e=
xception handling?

It's not just personal preference. It is an established pattern to
avoid extra NULL tests around kfree.

A quick git log to show a few recent examples of patches that expressly
remove such branches, e.g.,

commit d0110443cf4a ("amd/pds_core: core: No need for Null pointer check =
before kfree")
commit efd9d065de67 ("drm/radeon: Remove unnecessary NULL test before kfr=
ee in 'radeon_connector_free_edid'")

An interesting older thread on the topic:

https://linux-kernel.vger.kernel.narkive.com/KVjlDsTo/kfree-null

My summary, the many branches scattered throughout the kernel likely
are more expensive than the occasional save from seeing the rare NULL
pointer.