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=-7.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 1CA8FC43441 for ; Fri, 23 Nov 2018 11:31:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D036C20865 for ; Fri, 23 Nov 2018 11:31:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D036C20865 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2409654AbeKWWP3 (ORCPT ); Fri, 23 Nov 2018 17:15:29 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:42584 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388116AbeKWWP3 (ORCPT ); Fri, 23 Nov 2018 17:15:29 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 433ED3620; Fri, 23 Nov 2018 03:31:36 -0800 (PST) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.113]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 532A33F5A0; Fri, 23 Nov 2018 03:31:34 -0800 (PST) Date: Fri, 23 Nov 2018 11:31:31 +0000 From: Catalin Marinas To: Sebastian Andrzej Siewior Cc: Andrea Parri , Peter Zijlstra , zhe.he@windriver.com, tglx@linutronix.de, rostedt@goodmis.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, boqun.feng@gmail.com Subject: Re: [PATCH v2] kmemleak: Turn kmemleak_lock to raw spinlock on RT Message-ID: <20181123113130.GA3360@arrakis.emea.arm.com> References: <1542877459-144382-1-git-send-email-zhe.he@windriver.com> <20181123095314.hervxkxtqoixovro@linutronix.de> <20181123110226.GA5125@andrea> <20181123110611.s2gmd237j7docrxt@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181123110611.s2gmd237j7docrxt@linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 23, 2018 at 12:06:11PM +0100, Sebastian Andrzej Siewior wrote: > On 2018-11-23 12:02:55 [+0100], Andrea Parri wrote: > > > is this an RT-only problem? Because mainline should not allow read->read > > > locking or read->write locking for reader-writer locks. If this only > > > happens on v4.18 and not on v4.19 then something must have fixed it. > > > > Probably misunderstanding, but I'd say that read->read locking is "the > > norm"...? > > > > If you don't use qrwlock, readers are also "recursive", in part., > > > > P0 P1 > > read_lock(l) > > write_lock(l) > > read_lock(l) > > > > won't block P0 on the second read_lock(). (qrwlock somehow complicate > > the analysis; IIUC, they are recursive if and only if in_interrupt().). > > ehm, peterz, is that true? My memory on that is that all readers will > block if there is a writer pending. With qwrlocks, the readers will normally block if there is a pending writer (to avoid starving the writer), unless in_interrupt() when the readers are allowed to starve a pending writer. TLA+/PlusCal model here: ;) https://git.kernel.org/pub/scm/linux/kernel/git/cmarinas/kernel-tla.git/tree/qrwlock.tla -- Catalin