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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 B8342C433E2 for ; Tue, 8 Sep 2020 17:58:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F1B3206E7 for ; Tue, 8 Sep 2020 17:58:30 +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="TgU0nbUg" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732145AbgIHR63 (ORCPT ); Tue, 8 Sep 2020 13:58:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44994 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726591AbgIHR6V (ORCPT ); Tue, 8 Sep 2020 13:58:21 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7AD62C061573 for ; Tue, 8 Sep 2020 10:58:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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; bh=DO6W80RdfG9P9Z4fc9rbaY/MdeJfPrgZXo3Rg960r0c=; b=TgU0nbUgP8phE3d+0e2QoGBHwD feFtPdBAtdEUbNiMqPm/NVSd+CE+MM4/wZoKFaY/3kaNkarsSzAEcimpK4Do9wIl8maTrW1Du71hI zYZecYMsVtVLhzfUUyza+suNgTeHebQ9tS/p/NnPhV46tR8hb5sGj6vP7cQQJ7v3VRm4/NQZE4o0z MiknYyoeDKA44fWsJis4tcZnyeeGSMzSmr+aBA6WwkfNnxOv3vVdchd4A4Mtx9/JxBIMB6UqHe9uN IEoyAnN5V/5vTSoXA58/nEkv6c8+IFyOe0p9BxadW9g/kkC1i3MHF8x/igPFUkuECYrfkt6caA2j2 Js+InoZA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kFhsh-0006Ym-Vv; Tue, 08 Sep 2020 17:58:12 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 9ED99307590; Tue, 8 Sep 2020 19:58:08 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 8601D24C37E82; Tue, 8 Sep 2020 19:58:08 +0200 (CEST) Date: Tue, 8 Sep 2020 19:58:08 +0200 From: peterz@infradead.org To: Qian Cai Cc: mark.rutland@arm.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH -next] fork: silence a false postive warning in __mmdrop Message-ID: <20200908175808.GX1362448@hirez.programming.kicks-ass.net> References: <20200604150344.1796-1-cai@lca.pw> <20200722100637.GR119549@hirez.programming.kicks-ass.net> <20200722131900.GA4041@lca.pw> <20200722134406.GN10769@hirez.programming.kicks-ass.net> <20200908165043.GD5147@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200908165043.GD5147@lca.pw> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 08, 2020 at 12:50:44PM -0400, Qian Cai wrote: > > No, you're talking nonsense. We must not free @mm when > > 'current->active_mm == mm', never. > > Yes, you are right. It still trigger this below on powerpc with today's > linux-next by fuzzing for a while (saw a few times on recent linux-next before > as well but so far mostly reproducible on powerpc here). Any idea? If you can reliably reproduce this, the next thing is to trace mm_count and figure out where it goes side-ways. I suppose we're looking for an 'extra' decrement. Mark tried this for a while but gave up because he couldn't reliably reproduce.