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 X-Spam-Level: X-Spam-Status: No, score=-7.4 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5C175C48BE6 for ; Wed, 16 Jun 2021 15:03:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A82D6115C for ; Wed, 16 Jun 2021 15:03:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234406AbhFPPFI (ORCPT ); Wed, 16 Jun 2021 11:05:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32970 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234367AbhFPPFI (ORCPT ); Wed, 16 Jun 2021 11:05:08 -0400 Received: from hr2.samba.org (hr2.samba.org [IPv6:2a01:4f8:192:486::2:0]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0C0CAC061574 for ; Wed, 16 Jun 2021 08:03:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=samba.org; s=42; h=Date:Message-ID:From:Cc:To; bh=uKBlRJ7ES/51u1y4tRd7tSxIzq7coiUgU/ox3RFAAio=; b=1ATnlLJHwT7b5AyKzOzT7RGnUV Zjvzq9hymJZD1fbzgcJiRj6b49/PzLBsPV/eM3sS5k6FWng/9Rx7odBOr1EPZTsXreD8qpigeGRZh eThlNkLe10gB0DHS8N0S3aPCqnJQPSrylNTx2cA4Njz2hGslXptzIwVYGv2Zzo6lDfhXkRdyTd4U7 AKFr/zTni5qdLIgJdHzfwHi5Kiv9Oyuf+sM6mzq1ElcbjAp9+VbDH8EMw10o/QujF+o1/nr088YIq I9BU+ZcOYJBLNp7rjH3dj5fxF7O97Heyf4FKBa+kFRTPQce1JXoG3c4jJCkcPBJHJv2Y6xlyeZLLW nunv7mWr/HLw1SeThpfa7qofq1W2w5xevIt5lyY3zdBeInVHBO0+kN0oYUYyVdgDEzym8Epal9ZmR FBKLj7dwM8Z80yy+5XUgr6D9md9vK9OKM/c53/Vlg9QgGjafprvLlj0GRxXRgWVNVQUZTu4SDWebN BIGp4hNoiqhkwf+CC1BWYxp6; Received: from [127.0.0.2] (localhost [127.0.0.1]) by hr2.samba.org with esmtpsa (TLS1.3:ECDHE_RSA_CHACHA20_POLY1305:256) (Exim) id 1ltX4E-00034q-0v; Wed, 16 Jun 2021 15:02:58 +0000 Subject: Re: [PATCH for-next] RDMA/cma: Replace RMW with atomic bit-ops To: =?UTF-8?Q?H=c3=a5kon_Bugge?= , Doug Ledford , Jason Gunthorpe , Leon Romanovsky Cc: linux-rdma@vger.kernel.org References: <1623854153-19147-1-git-send-email-haakon.bugge@oracle.com> From: Stefan Metzmacher Message-ID: <70403927-7cd3-a9e2-6e97-d1bb35571db6@samba.org> Date: Wed, 16 Jun 2021 17:02:57 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <1623854153-19147-1-git-send-email-haakon.bugge@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org Hi Håkon, > +#define BIT_ACCESS_FUNCTIONS(b) \ > + static inline void set_##b(unsigned long flags) \ > + { \ > + /* set_bit() does not imply a memory barrier */ \ > + smp_mb__before_atomic(); \ > + set_bit(b, &flags); \ > + /* set_bit() does not imply a memory barrier */ \ > + smp_mb__after_atomic(); \ > + } \ Don't you need to pass flags by reference to the inline function? As far as I can see set_bit() operates on a temporary variable. In order to check if inline functions are special I wrote this little check: $ cat inline_arg.c #include static inline void func(unsigned s, unsigned *p) { printf("&s=%p p=%p\n", &s, p); } int main(void) { unsigned flags = 0; func(flags, &flags); return 0; } $ gcc -O0 -o inline_arg inline_arg.c $ ./inline_arg &s=0x7ffd3a71616c p=0x7ffd3a716184 $ gcc -O6 -o inline_arg inline_arg.c $ ./inline_arg &s=0x7ffd87781064 p=0x7ffd87781060 It means s doesn't magically become 'flags' of the caller... I'm I missing something? metze