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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 6D688C43441 for ; Mon, 26 Nov 2018 08:40:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2DC9820663 for ; Mon, 26 Nov 2018 08:40:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="UATschJS" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2DC9820663 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.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 S1726291AbeKZTeN (ORCPT ); Mon, 26 Nov 2018 14:34:13 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:36066 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726164AbeKZTeN (ORCPT ); Mon, 26 Nov 2018 14:34:13 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=dFfCRLDk1yob2SgCd+1I3aUGQ8QQYq7LIE7duVE0qvI=; b=UATschJSxShFT7IxiJ7jXlQ8N 5fMMMj2K30Isa1o0nO+HbuRB1pBoqpCB0mgty7P9LvOrwQYvJKvguqH9cvjmrhmoUgc0AZ0VqQuht upqHweYjyKoSrz2/QBtQnSPexRyZqswQyTGaUjpDIH6zulZNZ3crjyho+UNcj9wacWCQ1/6a00/Gj 3/53O6Sqj+NcqA/yt3ZaxIwInwswd6REMyBzMVsi6L8tGeZq0Rq5J3Ak28BqtLXWFFQYpxV4MWkAn ir0jY0cW2lvfBJ5EdciWxZSxGEXqsSqI9s96PgKQdUa5TgCf7Yr1+J6MkJGj5Yp2TiXYrRysOY4tV hWgTT3lZA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gRCRg-0002IN-0R; Mon, 26 Nov 2018 08:40:44 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 09C6B2029FD58; Mon, 26 Nov 2018 09:40:42 +0100 (CET) Date: Mon, 26 Nov 2018 09:40:42 +0100 From: Peter Zijlstra To: Sebastian Andrzej Siewior Cc: Andrea Parri , zhe.he@windriver.com, catalin.marinas@arm.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: <20181126084042.GK2113@hirez.programming.kicks-ass.net> 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. Since qrwlock is the more strict, all users should use its semantics. Just like we cannot 'rely' on the unfairness of some lock implementations.