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)