From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bmailout1.hostsharing.net (bmailout1.hostsharing.net [83.223.95.100]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ACE911F927 for ; Thu, 4 Jan 2024 06:57:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=wunner.de Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=h08.hostsharing.net Received: from h08.hostsharing.net (h08.hostsharing.net [IPv6:2a01:37:1000::53df:5f1c:0]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "*.hostsharing.net", Issuer "RapidSSL TLS RSA CA G1" (verified OK)) by bmailout1.hostsharing.net (Postfix) with ESMTPS id 61C6930000D09; Thu, 4 Jan 2024 07:57:44 +0100 (CET) Received: by h08.hostsharing.net (Postfix, from userid 100393) id 4131E24ADCF; Thu, 4 Jan 2024 07:57:44 +0100 (CET) Date: Thu, 4 Jan 2024 07:57:44 +0100 From: Lukas Wunner To: Peter Zijlstra Cc: Greg Kroah-Hartman , Dan Williams , linux-coco@lists.linux.dev, Andrew Morton , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 4/5] mm/slab: Add __free() support for kvfree Message-ID: <20240104065744.GA6055@wunner.de> References: <169199898909.1782217.10899362240465838600.stgit@dwillia2-xfh.jf.intel.com> <169199901230.1782217.9803098171993981037.stgit@dwillia2-xfh.jf.intel.com> <2023081449-blurry-bath-248e@gregkh> <20230814161731.GN776869@hirez.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230814161731.GN776869@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) On Mon, Aug 14, 2023 at 06:17:31PM +0200, Peter Zijlstra wrote: > On Mon, Aug 14, 2023 at 05:31:27PM +0200, Greg Kroah-Hartman wrote: > > On Mon, Aug 14, 2023 at 12:43:32AM -0700, Dan Williams wrote: > > > Allow for the declaration of variables that trigger kvfree() when they > > > go out of scope. > > > > > > Cc: Andrew Morton > > > Cc: Peter Zijlstra > > > Cc: Greg Kroah-Hartman > > > Signed-off-by: Dan Williams > > > --- > > > include/linux/slab.h | 2 ++ > > > 1 file changed, 2 insertions(+) > > > > > > diff --git a/include/linux/slab.h b/include/linux/slab.h > > > index 848c7c82ad5a..241025367943 100644 > > > --- a/include/linux/slab.h > > > +++ b/include/linux/slab.h > > > @@ -746,6 +746,8 @@ static inline __alloc_size(1, 2) void *kvcalloc(size_t n, size_t size, gfp_t fla > > > extern void *kvrealloc(const void *p, size_t oldsize, size_t newsize, gfp_t flags) > > > __realloc_size(3); > > > extern void kvfree(const void *addr); > > > +DEFINE_FREE(kvfree, void *, if (_T) kvfree(_T)) > > > > No need to check _T before calling this, right (as was also pointed out > > earlier). > > Well, that does mean you get an unconditional call to kvfree() in the > success case. Linus argued against this. > > This way the compiler sees: > > buf = NULL; > if (buf) > kvfree(buf); > > and goes: 'let me clean that up for you'. And all is well. Have you actually verified that assumption in the generated Assembler code? The kernel is compiled with -fno-delete-null-pointer-checks since commit a3ca86aea507 ("Add '-fno-delete-null-pointer-checks' to gcc CFLAGS"). So NULL pointer checks are *not* optimized away even if the compiler knows that a pointer is NULL. Background story: https://lwn.net/Articles/342330/ Thanks, Lukas