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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 222D7C43441 for ; Fri, 23 Nov 2018 11:06:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DA23520685 for ; Fri, 23 Nov 2018 11:06:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DA23520685 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de 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 S2409581AbeKWVuN (ORCPT ); Fri, 23 Nov 2018 16:50:13 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:50109 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731891AbeKWVuM (ORCPT ); Fri, 23 Nov 2018 16:50:12 -0500 Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1gQ9Hn-0004cl-O2; Fri, 23 Nov 2018 12:06:11 +0100 Date: Fri, 23 Nov 2018 12:06:11 +0100 From: Sebastian Andrzej Siewior To: Andrea Parri , Peter Zijlstra Cc: 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: <20181123110611.s2gmd237j7docrxt@linutronix.de> References: <1542877459-144382-1-git-send-email-zhe.he@windriver.com> <20181123095314.hervxkxtqoixovro@linutronix.de> <20181123110226.GA5125@andrea> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181123110226.GA5125@andrea> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > Andrea Sebastian