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=-9.0 required=3.0 tests=BAYES_00,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 DA18BC2B9F4 for ; Tue, 22 Jun 2021 17:27:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B587961075 for ; Tue, 22 Jun 2021 17:27:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231133AbhFVR3m (ORCPT ); Tue, 22 Jun 2021 13:29:42 -0400 Received: from mail-pj1-f47.google.com ([209.85.216.47]:52144 "EHLO mail-pj1-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230330AbhFVR3l (ORCPT ); Tue, 22 Jun 2021 13:29:41 -0400 Received: by mail-pj1-f47.google.com with SMTP id k5so12497084pjj.1; Tue, 22 Jun 2021 10:27:25 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=TDTX8YmbiwRpMt6jiQDt+NdG80VPPhT2S2LVoaPP0rs=; b=RFTMa0V2woewcfzp5E284NtKiIb2rXKO8QkG4vswWqbx2ClQO4wiM0cos5baRT4fth zaLi+A1605DtrZ9MQQ1ahwmWQCPhELKbFValBYsedPGcDggPqB6Ge5tQQaPEd/leo9aq Jt1zE6k5FCWu7ba+TWe5R1BPFp0iWjWraxFhHdrjQ15maL3VFLlj2Rn/55ccUH/bgh89 phAxsKAaO2Lea8OE7+z8ntUGpaV0Us1MFU75IJNrGibbCJihLv6WAqaRM9vUCzF1VC+9 mQMlAFDQnQDdqUcmxqX7rgoxXE2vhCNoBy+vm0eb6+1HoLgGa/c681daj2ehftCGkyZA lKsw== X-Gm-Message-State: AOAM531Ar1YYK0a2sPH9dWkZbaXoL+0HRcoSill8zdGXks6pL7phT1gx 8jdenefGPWglJzAmWzx7/s8= X-Google-Smtp-Source: ABdhPJzJN6ws+q6XGvkAUn6iRQ7P0VAa8qBTM9yPcb1TWTfPDNt+hIQrqpHoOrP9wB5tvWW0IwlJqA== X-Received: by 2002:a17:902:d489:b029:126:60a0:4797 with SMTP id c9-20020a170902d489b029012660a04797mr5197952plg.5.1624382845401; Tue, 22 Jun 2021 10:27:25 -0700 (PDT) Received: from garbanzo ([173.239.198.97]) by smtp.gmail.com with ESMTPSA id y20sm21724868pfb.207.2021.06.22.10.27.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Jun 2021 10:27:15 -0700 (PDT) Date: Tue, 22 Jun 2021 10:27:12 -0700 From: Luis Chamberlain To: Greg KH Cc: minchan@kernel.org, jeyu@kernel.org, ngupta@vflare.org, sergey.senozhatsky.work@gmail.com, axboe@kernel.dk, mbenes@suse.com, jpoimboe@redhat.com, tglx@linutronix.de, keescook@chromium.org, jikos@kernel.org, rostedt@goodmis.org, peterz@infradead.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 2/3] zram: fix deadlock with sysfs attribute usage and driver removal Message-ID: <20210622172712.3bdlxnsghmbn6nry@garbanzo> References: <20210621233013.562641-1-mcgrof@kernel.org> <20210621233634.595649-1-mcgrof@kernel.org> <20210622163208.epx4lf3pv2x2d5b4@garbanzo> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Jun 22, 2021 at 07:16:34PM +0200, Greg KH wrote: > On Tue, Jun 22, 2021 at 09:32:08AM -0700, Luis Chamberlain wrote: > > On Tue, Jun 22, 2021 at 09:45:39AM +0200, Greg KH wrote: > > > On Mon, Jun 21, 2021 at 04:36:34PM -0700, Luis Chamberlain wrote: > > > > @@ -2048,13 +2048,19 @@ static ssize_t hot_add_show(struct class *class, > > > > { > > > > int ret; > > > > > > > > + if (!try_module_get(THIS_MODULE)) > > > > + return -ENODEV; > > > > + > > > > > > You can not increment/decrement your own module's reference count and > > > expect it to work properly, as it is still a race. > > > > The goal here is to prevent an rmmod call if this succeeds. If it > > succeeds then any subsequent rmmod will fail. Can you explain how > > this is still racy? > > {sigh} > > What happens if the driver core is just about to call hot_add_show() and > the module is removed from the system. It then calls to the memory > location that hot_add_show() was previously at, but now that is not a > valid pointer to code, and boom. The new kobject_get() on patch 3/3 ensures that the device will be up throughout the entire life of the store call, and thus prevent the code being executed being removed, no? Luis