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=-6.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_PASS 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 F1896C43441 for ; Fri, 23 Nov 2018 15:51:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 925F420824 for ; Fri, 23 Nov 2018 15:51:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 925F420824 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org 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 S2436682AbeKXCgT (ORCPT ); Fri, 23 Nov 2018 21:36:19 -0500 Received: from mail.kernel.org ([198.145.29.99]:34734 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391042AbeKXCgT (ORCPT ); Fri, 23 Nov 2018 21:36:19 -0500 Received: from vmware.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 763DF205C9; Fri, 23 Nov 2018 15:51:34 +0000 (UTC) Date: Fri, 23 Nov 2018 10:51:32 -0500 From: Steven Rostedt To: Catalin Marinas Cc: Sebastian Andrzej Siewior , Andrea Parri , Peter Zijlstra , zhe.he@windriver.com, tglx@linutronix.de, 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: <20181123105132.47ee57ad@vmware.local.home> In-Reply-To: <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> <20181123113130.GA3360@arrakis.emea.arm.com> X-Mailer: Claws Mail 3.15.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 23 Nov 2018 11:31:31 +0000 Catalin Marinas wrote: > 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 > And the code appears to confirm it too: void queued_read_lock_slowpath(struct qrwlock *lock) { /* * Readers come here when they cannot get the lock without waiting */ if (unlikely(in_interrupt())) { /* * Readers in interrupt context will get the lock immediately * if the writer is just waiting (not holding the lock yet), * so spin with ACQUIRE semantics until the lock is available * without waiting in the queue. */ atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED)); return; } atomic_sub(_QR_BIAS, &lock->cnts); /* * Put the reader into the wait queue */ arch_spin_lock(&lock->wait_lock); atomic_add(_QR_BIAS, &lock->cnts); -- Steve