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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DBD1AC4321E for ; Tue, 26 Oct 2021 17:02:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C42D760E08 for ; Tue, 26 Oct 2021 17:02:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237638AbhJZREc (ORCPT ); Tue, 26 Oct 2021 13:04:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34936 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231360AbhJZRE0 (ORCPT ); Tue, 26 Oct 2021 13:04:26 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CBD49C061745; Tue, 26 Oct 2021 10:02:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=rokadze8fRogRPO3TrlkJtrH8Z7jdFewFpbGPuZXCIM=; b=Qu7hbKOTAdEdBAA2y8tI88Y2/9 fLNwaKezOpXserGMaIVWN2jN15mgeYqvk8M/nMFdvuU5t2HO/FTeOt9d2UnO/Ggl4TZKbTQdsz+G4 nXL1XP7usNiHTBSnuvt5MSW3VpiWZscPz5mEn0nHDheFG/gaH7XQRVOfMfyO9X9MK1IREmP9s72mA QTDix5gCEW/5udqqkrYa156daZNZ2zGDGhygkQ21zCMafu9t/D+JajvGykPFMZdU/SiIGrSpnAD0A 1UKOvtUSFjhuxsuXZjboMKtwJV73xZGh8YYSz/Tknj3RKEaQ8H8Afu4sGA/11uH8N2/HPJ0IdzpiW RZAtoISw==; Received: from mcgrof by bombadil.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mfPpV-002Yak-03; Tue, 26 Oct 2021 17:01:41 +0000 Date: Tue, 26 Oct 2021 10:01:40 -0700 From: Luis Chamberlain To: Ming Lei , Julia Lawall Cc: Petr Mladek , Miroslav Benes , Benjamin Herrenschmidt , Paul Mackerras , tj@kernel.org, gregkh@linuxfoundation.org, akpm@linux-foundation.org, minchan@kernel.org, jeyu@kernel.org, shuah@kernel.org, bvanassche@acm.org, dan.j.williams@intel.com, joe@perches.com, tglx@linutronix.de, keescook@chromium.org, rostedt@goodmis.org, linux-spdx@vger.kernel.org, linux-doc@vger.kernel.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Subject: Re: [PATCH v8 11/12] zram: fix crashes with cpu hotplug multistate Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Luis Chamberlain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 26, 2021 at 11:37:30PM +0800, Ming Lei wrote: > On Tue, Oct 26, 2021 at 10:48:18AM +0200, Petr Mladek wrote: > > Livepatch code never called kobject_del() under a lock. It would cause > > the obvious deadlock. Never? > > The historic code only waited in the > > module_exit() callback until the sysfs interface was removed. > > OK, then Luis shouldn't consider livepatching as one such issue to solve > with one generic solution. It's not what I was told when the deadlock was found with zram, so I was informed quite the contrary. I'm working on a generic coccinelle patch which hunts for actual cases using iteration (a feature of coccinelle for complex searches). The search is pretty involved, so I don't think I'll have an answer to this soon. Since the question of how generic this deadlock is remains questionable, I think it makes sense to put the generic deadlock fix off the table for now, and we address this once we have a more concrete search with coccinelle. But to say we *don't* have drivers which can cause this is obviously wrong as well, from a cursory search so far. But let's wait and see how big this list actually is. I'll drop the deadlock generic fixes and move on with at least a starter kernfs / sysfs tests. Luis