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 0F470C63797 for ; Tue, 10 Jan 2023 12:46:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237906AbjAJMqz (ORCPT ); Tue, 10 Jan 2023 07:46:55 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55814 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232488AbjAJMqy (ORCPT ); Tue, 10 Jan 2023 07:46:54 -0500 Received: from mga12.intel.com (mga12.intel.com [192.55.52.136]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1C65A4FCE9; Tue, 10 Jan 2023 04:46:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1673354813; x=1704890813; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=JjCURNXFRNcYm6qc3FnZISad0UB5+7XjMdbu/B0f1Fo=; b=dBrSK8pUnAS9DlR5De4m4pGHPecuaVHYMOsvE9RqaUG3SSw2qPeWTZfs W+PrO6Po2RHkqnb+9zT21BLK6wIzaPP8OsUZVMw8KFYBiNTXPXWMHIJpx AWF0Dj8pgsKkrLSvE1PjW87tU4ZXbtx2Ca9i3OezaoCL8hipF4R5Y9+O5 +PiifomgFNqirtFV9/ZIAuElGDzY1ncKdp5K1AqZke6sDbq5g8nI5vZdn QVNsAyernmi3Pbmbx9/MuV9liHxBZNFcbOchudK/9+WZXXOSCo0oys6ZB tdGdxNHzBAZzhJcmSH4eL9FBj7NvhMMWoE+MpU32zpeciq0FrBr/GYkPc Q==; X-IronPort-AV: E=McAfee;i="6500,9779,10585"; a="302834344" X-IronPort-AV: E=Sophos;i="5.96,315,1665471600"; d="scan'208";a="302834344" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Jan 2023 04:46:46 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10585"; a="689393555" X-IronPort-AV: E=Sophos;i="5.96,315,1665471600"; d="scan'208";a="689393555" Received: from ahajda-mobl.ger.corp.intel.com (HELO [10.213.8.19]) ([10.213.8.19]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Jan 2023 04:46:39 -0800 Message-ID: <1bfae3d0-8c0b-ea83-7184-db847a4a969f@intel.com> Date: Tue, 10 Jan 2023 13:46:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Firefox/102.0 Thunderbird/102.6.1 Subject: Re: [Intel-gfx] [RFC DO NOT MERGE] treewide: use __xchg in most obvious places Content-Language: en-US To: Andy Shevchenko Cc: Mark Rutland , linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Peter Zijlstra , dri-devel@lists.freedesktop.org, linux-mips@vger.kernel.org, sparclinux@vger.kernel.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-snps-arc@lists.infradead.org, Boqun Feng , linux-xtensa@linux-xtensa.org, Arnd Bergmann , intel-gfx@lists.freedesktop.org, linux-m68k@lists.linux-m68k.org, openrisc@lists.librecores.org, loongarch@lists.linux.dev, Rodrigo Vivi , linux-arm-kernel@lists.infradead.org, linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, Daniel Vetter , linux-alpha@vger.kernel.org, Andrew Morton , linuxppc-dev@lists.ozlabs.org References: <20230110105306.3973122-1-andrzej.hajda@intel.com> From: Andrzej Hajda Organization: Intel Technology Poland sp. z o.o. - ul. Slowackiego 173, 80-298 Gdansk - KRS 101882 - NIP 957-07-52-316 In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On 10.01.2023 12:07, Andy Shevchenko wrote: > 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. IMHO it is not needed also before the change and IIRC gcc has an extension which allows to drop (u8 *) cast as well [1]. [1]: https://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html > >> } > > ... > > Btw, is it done by coccinelle? If no, why not providing the script? > Yes I have used cocci. My cocci skills are far from perfect, so I did not want to share my dirty code, but this is nothing secret: @r1@ expression x, v; local idexpression p; @@ - p = x; - x = v; - return p; + return __xchg(&x, v); @depends on r1@ expression e; @@ __xchg( - &*e, + e, ...) @depends on r1@ expression t; @@ - if (t) { + if (t) return __xchg(...); - } @depends on r1@ type t; identifier p; expression e; @@ ( - t p; | - t p = e; ) ... when != p Regards Andrzej