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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 0568EC49361 for ; Thu, 17 Jun 2021 11:52:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D741761159 for ; Thu, 17 Jun 2021 11:52:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232395AbhFQLyJ (ORCPT ); Thu, 17 Jun 2021 07:54:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57188 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230269AbhFQLyF (ORCPT ); Thu, 17 Jun 2021 07:54:05 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A2976C061574; Thu, 17 Jun 2021 04:51:57 -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=eWfLpTUm88WigYNAtGgk0puveZH4s8vjCO/lhD+KZFA=; b=Ksd9U+/hjhk7n5mA5nDGHYSxdq ZjKymSIxqpChMzh0uIjvW46GqzQIAUbUkc2KgZ9iAtw8Occ48KXpEdrwhf1V/SOTILfcoq15YzLe3 pd2CTMHOibHCqPeQRFeJ+4BC4ILcOzzZlwMQ2XJdFSZSJQvxqsSIiiB86v16VD2X6LhGwWc2G4m1t uFkCcygCch96mtPisbW0Rcu8S0F+xiZ7w0iBJigWj0LIkJiT4+ftv1HKs+Gl2mWC+/9jGuRXczqQu giuqpDjJl4ppLa1xG1/FiE+jjtHCtzBVDRSSiR/xwcuf8YQMDOUoC40mvQmMTWu7Ez0sr24mI8Vhz GU+A0e7g==; Received: from hch by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1ltqYN-0095Tm-BZ; Thu, 17 Jun 2021 11:51:30 +0000 Date: Thu, 17 Jun 2021 12:51:23 +0100 From: Christoph Hellwig To: Desmond Cheong Zhi Xi Cc: axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, gregkh@linuxfoundation.org, linux-kernel-mentees@lists.linuxfoundation.org, syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com, miquel.raynal@bootlin.com, richard@nod.at, vigneshr@ti.com, linux-mtd@lists.infradead.org Subject: Re: [PATCH] block: break circular locks in blk_request_module Message-ID: References: <20210617092016.522985-1-desmondcheongzx@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210617092016.522985-1-desmondcheongzx@gmail.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 17, 2021 at 05:20:16PM +0800, Desmond Cheong Zhi Xi wrote: > mutex_lock(&major_names_lock); > for (n = &major_names[major_to_index(major)]; *n; n = &(*n)->next) { > if ((*n)->major == major && (*n)->probe) { > - (*n)->probe(devt); > + probe = (*n)->probe; > mutex_unlock(&major_names_lock); > + probe(devt); And now you can all probe after it has been freed and/or the module has been unloaded. The obviously correct fix is to only hold mtd_table_mutex for the actually required critical section: diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c index fb8e12d590a1..065d94f9b1fb 100644 --- a/drivers/mtd/mtd_blkdevs.c +++ b/drivers/mtd/mtd_blkdevs.c @@ -529,13 +529,11 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr) register_mtd_user(&blktrans_notifier); - mutex_lock(&mtd_table_mutex); ret = register_blkdev(tr->major, tr->name); if (ret < 0) { printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n", tr->name, tr->major, ret); - mutex_unlock(&mtd_table_mutex); return ret; } @@ -545,12 +543,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr) tr->blkshift = ffs(tr->blksize) - 1; INIT_LIST_HEAD(&tr->devs); - list_add(&tr->list, &blktrans_majors); + mutex_lock(&mtd_table_mutex); + list_add(&tr->list, &blktrans_majors); mtd_for_each_device(mtd) if (mtd->type != MTD_ABSENT) tr->add_mtd(tr, mtd); - mutex_unlock(&mtd_table_mutex); return 0; }