From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E2186C678D8 for ; Tue, 10 Jan 2023 11:09:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232501AbjAJLI7 (ORCPT ); Tue, 10 Jan 2023 06:08:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50952 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238064AbjAJLHx (ORCPT ); Tue, 10 Jan 2023 06:07:53 -0500 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CBA601EEFB; Tue, 10 Jan 2023 03:07:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1673348836; x=1704884836; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=rVhJmEIPGip77/doSmIyFH6N4wuSe2EOVqkHy4zJTJM=; b=MIKStdG8ONY+3CPdc0beg1TZuGsXBoparQGrNjpOC/DIEvZ2wbfj/m3T NrxQmt3ovC6Liifr9aYKzx9xYUDHagztjo+dR6j+fHjkdr5bH0bncoi47 1Uwdw8U2YbewknyAjW6ZkVNKaN6gWshLneuLVdIb1KlsZ2lkAfKEG2Ur3 hPlaiBHKz0C31tA3R/Z0XnmZ9kmOuyi8BD2xdZxXJG1Kn0MqoZ3bV+IdV Y65lzN3mS1Ov/60lE+0H03e+Y67E2zmFG1Wmjl7IOiSOvU8rat7T4Rj/P p5Wxo7oYECXP1TBc0vucjhadvlKHJTEZ1KRCgezXj3lDTc85mM8++iVpi w==; X-IronPort-AV: E=McAfee;i="6500,9779,10585"; a="325123958" X-IronPort-AV: E=Sophos;i="5.96,315,1665471600"; d="scan'208";a="325123958" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Jan 2023 03:07:13 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6500,9779,10585"; a="745739146" X-IronPort-AV: E=Sophos;i="5.96,315,1665471600"; d="scan'208";a="745739146" Received: from smile.fi.intel.com ([10.237.72.54]) by FMSMGA003.fm.intel.com with ESMTP; 10 Jan 2023 03:07:05 -0800 Received: from andy by smile.fi.intel.com with local (Exim 4.96) (envelope-from ) id 1pFCT8-006ztV-3A; Tue, 10 Jan 2023 13:07:02 +0200 Date: Tue, 10 Jan 2023 13:07:02 +0200 From: Andy Shevchenko To: Andrzej Hajda Cc: Daniel Vetter , linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, loongarch@lists.linux.dev, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, openrisc@lists.librecores.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Arnd Bergmann , Rodrigo Vivi , Andrew Morton , Peter Zijlstra , Boqun Feng , Mark Rutland Subject: Re: [RFC DO NOT MERGE] treewide: use __xchg in most obvious places Message-ID: References: <20230110105306.3973122-1-andrzej.hajda@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230110105306.3973122-1-andrzej.hajda@intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 10, 2023 at 11:53:06AM +0100, Andrzej Hajda wrote: > This patch tries to show usability of __xchg helper. > It is not intended to be merged, but I can convert > it to proper patchset if necessary. > > There are many more places where __xchg can be used. > This demo shows the most spectacular cases IMHO: > - previous value is returned from function, > - temporary variables are in use. > > As a result readability is much better and diffstat is quite > nice, less local vars to look at. > In many cases whole body of functions is replaced > with __xchg(ptr, val), so as further refactoring the whole > function can be removed and __xchg can be called directly. ... > arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, > struct pt_regs *regs) > { > - unsigned long orig_ret_vaddr; > - > - orig_ret_vaddr = regs->ARM_lr; > - /* Replace the return addr with trampoline addr */ > - regs->ARM_lr = trampoline_vaddr; > - return orig_ret_vaddr; > + return __xchg(®s->ARM_lr, trampoline_vaddr); > } If it's not a callback, the entire function can be killed. And this is a good example of the function usage. OTOH, these places might have a side effect (if it's in deep CPU handlers), means we need to do this carefully. ... > static inline void *qed_chain_produce(struct qed_chain *p_chain) > { > - void *p_ret = NULL, *p_prod_idx, *p_prod_page_idx; > + void *p_prod_idx, *p_prod_page_idx; > > if (is_chain_u16(p_chain)) { > if ((p_chain->u.chain16.prod_idx & > @@ -390,11 +391,8 @@ static inline void *qed_chain_produce(struct qed_chain *p_chain) > p_chain->u.chain32.prod_idx++; > } > > - p_ret = p_chain->p_prod_elem; > - p_chain->p_prod_elem = (void *)(((u8 *)p_chain->p_prod_elem) + > - p_chain->elem_size); > - > - return p_ret; > + return __xchg(&p_chain->p_prod_elem, > + (void *)(((u8 *)p_chain->p_prod_elem) + p_chain->elem_size)); Wondering if you still need a (void *) casting after the change. Ditto for the rest of similar cases. > } ... Btw, is it done by coccinelle? If no, why not providing the script? -- With Best Regards, Andy Shevchenko