From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) (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 89EAC7C for ; Wed, 17 Aug 2022 08:20:12 +0000 (UTC) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-186-_ZDhN8jUN4OlHtEkOqfydg-1; Wed, 17 Aug 2022 09:20:09 +0100 X-MC-Unique: _ZDhN8jUN4OlHtEkOqfydg-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.38; Wed, 17 Aug 2022 09:20:08 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.040; Wed, 17 Aug 2022 09:20:08 +0100 From: David Laight To: 'Hector Martin' , Will Deacon , "Peter Zijlstra" , Arnd Bergmann , Ingo Molnar CC: Alan Stern , Andrea Parri , Boqun Feng , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , "Paul E. McKenney" , Akira Yokosawa , "Daniel Lustig" , Joel Fernandes , "Mark Rutland" , Jonathan Corbet , Tejun Heo , "jirislaby@kernel.org" , Marc Zyngier , Catalin Marinas , Oliver Neukum , Linus Torvalds , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Asahi Linux , "stable@vger.kernel.org" Subject: RE: [PATCH] locking/atomic: Make test_and_*_bit() ordered on failure Thread-Topic: [PATCH] locking/atomic: Make test_and_*_bit() ordered on failure Thread-Index: AQHYsU4vfwz5idsf402HoI6nUKdp962yvvCA Date: Wed, 17 Aug 2022 08:20:08 +0000 Message-ID: <1135281ad4e84cc5ac0147772aa83787@AcuMS.aculab.com> References: <20220816070311.89186-1-marcan@marcan.st> In-Reply-To: <20220816070311.89186-1-marcan@marcan.st> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] Precedence: bulk X-Mailing-List: asahi@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable ... > =09p +=3D BIT_WORD(nr); > -=09if (READ_ONCE(*p) & mask) > -=09=09return 1; > - > =09old =3D arch_atomic_long_fetch_or(mask, (atomic_long_t *)p); > =09return !!(old & mask); > } This looks like the same pattern (attempting to avoid a locked bus cycle) that caused the qdisc code to sit on transmit packets (even on x86). That had some barriers in it (possibly nops on x86) that didn't help - although the comments suggested otherwise. I wonder if the pattern has been used anywhere else? =09David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales) 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 35B49C25B08 for ; Wed, 17 Aug 2022 08:21:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:In-Reply-To:References: Message-ID:Date:Subject:CC:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=fp7ZewMYYzh0hJjLK5xAUVy/geaAn2ae55nguVaOvxU=; b=SzGYne6AhaP3te o6rMyxa5C3EmGUrROC2R9ZIg3gv2U7G6TPIfclIoaFRBT9qtwdZ1H9AKYJ6X2MzBWHYp86rJ9gGds aiWf+yUkVzIHvois6Hjcw5SqfeZVJj+CiJ8rthVmneeH6G0kguTOYBm7kB/nBJPlUvT1E+NGYPlhe aszE0VaeqqA4EprY7pgvX2AOThGS7476kdgl9hi34Ys1qb9qdweAR29KbiUkofJy/DfEijZdIG178 gbsbyVQx+aqr4lFOSn732OtgSutXTH3ZvxdEEaAYOvB4uruCm8AprSb7JlOQBrOzV1JmZYJ6g5lN2 SLVcdBNvShLMQQ7F4L9A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oOEHr-00EqwK-DY; Wed, 17 Aug 2022 08:20:28 +0000 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.85.151]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1oOEHi-00EqgP-9N for linux-arm-kernel@lists.infradead.org; Wed, 17 Aug 2022 08:20:21 +0000 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-186-_ZDhN8jUN4OlHtEkOqfydg-1; Wed, 17 Aug 2022 09:20:09 +0100 X-MC-Unique: _ZDhN8jUN4OlHtEkOqfydg-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.38; Wed, 17 Aug 2022 09:20:08 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.040; Wed, 17 Aug 2022 09:20:08 +0100 From: David Laight To: 'Hector Martin' , Will Deacon , "Peter Zijlstra" , Arnd Bergmann , Ingo Molnar CC: Alan Stern , Andrea Parri , Boqun Feng , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , "Paul E. McKenney" , Akira Yokosawa , "Daniel Lustig" , Joel Fernandes , "Mark Rutland" , Jonathan Corbet , Tejun Heo , "jirislaby@kernel.org" , Marc Zyngier , Catalin Marinas , Oliver Neukum , Linus Torvalds , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Asahi Linux , "stable@vger.kernel.org" Subject: RE: [PATCH] locking/atomic: Make test_and_*_bit() ordered on failure Thread-Topic: [PATCH] locking/atomic: Make test_and_*_bit() ordered on failure Thread-Index: AQHYsU4vfwz5idsf402HoI6nUKdp962yvvCA Date: Wed, 17 Aug 2022 08:20:08 +0000 Message-ID: <1135281ad4e84cc5ac0147772aa83787@AcuMS.aculab.com> References: <20220816070311.89186-1-marcan@marcan.st> In-Reply-To: <20220816070311.89186-1-marcan@marcan.st> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220817_012018_651207_A6B75E0A X-CRM114-Status: UNSURE ( 8.82 ) X-CRM114-Notice: Please train this message. X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org ... > p += BIT_WORD(nr); > - if (READ_ONCE(*p) & mask) > - return 1; > - > old = arch_atomic_long_fetch_or(mask, (atomic_long_t *)p); > return !!(old & mask); > } This looks like the same pattern (attempting to avoid a locked bus cycle) that caused the qdisc code to sit on transmit packets (even on x86). That had some barriers in it (possibly nops on x86) that didn't help - although the comments suggested otherwise. I wonder if the pattern has been used anywhere else? David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel