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 B1820C433EF for ; Tue, 19 Oct 2021 09:24:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 95E516103B for ; Tue, 19 Oct 2021 09:24:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235064AbhJSJ0f (ORCPT ); Tue, 19 Oct 2021 05:26:35 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:46101 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235055AbhJSJ0d (ORCPT ); Tue, 19 Oct 2021 05:26:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1634635460; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=wmbGZV2ZKwLQrOAxpGl2pHHhTDBQE+6LCzInPZcyFEo=; b=hHV+57siKZcYdbWwnqDJirAKS/yKUgDXSSpQUOUfFy6Bc7rgSZ+z5E77P4UEKw8FDlANru boQgcED7MzkcZvHqd8vbsylKKbJiBF5LqnVz5Pocn5yJqCZAXSAHB75fiiX5tMyV0ywcSI sxpzLGKpUOKgK3NxMGNvLnFeBMViQV4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-390-Lm_WcdWwPiKJafreVln3Gg-1; Tue, 19 Oct 2021 05:24:16 -0400 X-MC-Unique: Lm_WcdWwPiKJafreVln3Gg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9044B802575; Tue, 19 Oct 2021 09:24:12 +0000 (UTC) Received: from T590 (ovpn-8-39.pek2.redhat.com [10.72.8.39]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 612425D6D5; Tue, 19 Oct 2021 09:23:55 +0000 (UTC) Date: Tue, 19 Oct 2021 17:23:50 +0800 From: Ming Lei To: Miroslav Benes Cc: Luis Chamberlain , 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, ming.lei@redhat.com 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: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Oct 19, 2021 at 08:23:51AM +0200, Miroslav Benes wrote: > > > By you only addressing the deadlock as a requirement on approach a) you are > > > forgetting that there *may* already be present drivers which *do* implement > > > such patterns in the kernel. I worked on addressing the deadlock because > > > I was informed livepatching *did* have that issue as well and so very > > > likely a generic solution to the deadlock could be beneficial to other > > > random drivers. > > > > In-tree zram doesn't have such deadlock, if livepatching has such AA deadlock, > > just fixed it, and seems it has been fixed by 3ec24776bfd0. > > I would not call it a fix. It is a kind of ugly workaround because the > generic infrastructure lacked (lacks) the proper support in my opinion. > Luis is trying to fix that. What is the proper support of the generic infrastructure? I am not familiar with livepatching's model(especially with module unload), you mean livepatching have to do the following way from sysfs: 1) during module exit: mutex_lock(lp_lock); kobject_put(lp_kobj); mutex_unlock(lp_lock); 2) show()/store() method of attributes of lp_kobj mutex_lock(lp_lock) ... mutex_unlock(lp_lock) IMO, the above usage simply caused AA deadlock. Even in Luis's patch 'zram: fix crashes with cpu hotplug multistate', new/same AA deadlock (hot_remove_store() vs. disksize_store() or reset_store()) is added because hot_remove_store() isn't called from module_exit(). Luis tries to delay unloading module until all show()/store() are done. But that can be obtained by the following way simply during module_exit(): kobject_del(lp_kobj); //all pending store()/show() from lp_kobj are done, //no new store()/show() can come after //kobject_del() returns mutex_lock(lp_lock); kobject_put(lp_kobj); mutex_unlock(lp_lock); Or can you explain your requirement on kobject/module unload in a bit details? Thanks, Ming