From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com [115.124.30.130]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CAB70320380; Fri, 31 Oct 2025 14:44:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.130 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761921901; cv=none; b=sNDDZYS30ndeW1k0tUBe5yn1Ag2UCom8nuoS9CQtiDm2+Q91kpRbqby4biMpJ472aBKFlabvydYMl7AeHiYO9C2OsjtzpTvccZbWZXwu6cYqWHhivc/AJD/aQcpe3ezxz6kw65OrDsLRRnqceqMsfIJl/iM9V0SNwORA+HDt5Ug= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761921901; c=relaxed/simple; bh=Gd5KBjx2srwmWtROjooqn9fjQrwaUhRPcZIt8Eqh+rs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GSAUUgcNG25SfZugYfJDeRB8rF0Qle7jYhhrjsoNDP+Y48+rhuJmzZNPp23kYMkFGRohKUD2eKRdUlUW2n+o134V4X0wKS6TEUkqOw5Tupl+esFtdYEVg2KZ7MLRYY1mKbK6hGhUfCTIY0whdgFAFrFb9iddEkeS1pRVdauqk4w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=HuKKeMF9; arc=none smtp.client-ip=115.124.30.130 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="HuKKeMF9" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1761921895; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=PfnYeDOw3NuHK44krWvx1RX9+ezQqo1kKRV2b1ByzRE=; b=HuKKeMF9clBJikaLLZFn3CWI2aTtS6z7YzOAxuNbMitES689mwiLQFs5oL7sWyk1qsoUHoOKK5zxpMTSrPjyjAVBl6ClqwbM74cSDUSfAIdXH9LTTCnaV6de9GnERfbK10G4yf4Gv/LuMe4L9C/h2tj1Y0ejiHZSa2y3ZeJQiaE= Received: from 30.180.79.37(mailfrom:hsiangkao@linux.alibaba.com fp:SMTPD_---0WrPDkzZ_1761921893 cluster:ay36) by smtp.aliyun-inc.com; Fri, 31 Oct 2025 22:44:54 +0800 Message-ID: <83b9dac8-815e-4990-8cc7-5aaf4ba85f42@linux.alibaba.com> Date: Fri, 31 Oct 2025 22:44:53 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: question about bd_inode hashing against device_add() // Re: [PATCH 03/11] block: call bdev_add later in device_add_disk To: Greg Kroah-Hartman Cc: Christoph Hellwig , Jens Axboe , Jan Kara , Christian Brauner , "Michael S. Tsirkin" , Jason Wang , "Martin K. Petersen" , Luis Chamberlain , linux-block@vger.kernel.org, Joseph Qi , guanghuifeng@linux.alibaba.com, zongyong.wzy@alibaba-inc.com, zyfjeff@linux.alibaba.com, "Rafael J. Wysocki" , Danilo Krummrich , linux-kernel@vger.kernel.org References: <20210818144542.19305-1-hch@lst.de> <20210818144542.19305-4-hch@lst.de> <43375218-2a80-4a7a-b8bb-465f6419b595@linux.alibaba.com> <20251031090925.GA9379@lst.de> <20251031094552.GA10011@lst.de> <7d0d8480-13a2-449f-a46d-d9b164d44089@linux.alibaba.com> <2025103155-definite-stays-ebfe@gregkh> <2a9ab583-07fc-4147-949e-7c68feda82f2@linux.alibaba.com> <2025103106-proposal-jogging-a076@gregkh> From: Gao Xiang In-Reply-To: <2025103106-proposal-jogging-a076@gregkh> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2025/10/31 22:34, Greg Kroah-Hartman wrote: > On Fri, Oct 31, 2025 at 08:23:32PM +0800, Gao Xiang wrote: >> >> >> On 2025/10/31 18:12, Gao Xiang wrote: >>> Hi Greg, >>> >>> On 2025/10/31 17:58, Greg Kroah-Hartman wrote: >>>> On Fri, Oct 31, 2025 at 05:54:10PM +0800, Gao Xiang wrote: >>>>> >>>>> >>>>> On 2025/10/31 17:45, Christoph Hellwig wrote: >> >> ... >> >>>>>> But why does the device node >>>>>> get created earlier?  My assumption was that it would only be >>>>>> created by the KOBJ_ADD uevent.  Adding the device model maintainers >>>>>> as my little dig through the core drivers/base/ code doesn't find >>>>>> anything to the contrary, but maybe I don't fully understand it. >>>>> >>>>> AFAIK, device_add() is used to trigger devtmpfs file >>>>> creation, and it can be observed if frequently >>>>> hotpluging device in the VM and mount.  Currently >>>>> I don't have time slot to build an easy reproducer, >>>>> but I think it's a real issue anyway. >>>> >>>> As I say above, that's not normal, and you have to be root to do this, >> I just spent time to reproduce with dynamic loop devices and >> actually it's easy if msleep() is located artificiallly, >> the diff as below: >> >> diff --git a/block/bdev.c b/block/bdev.c >> index 810707cca970..a4273b5ad456 100644 >> --- a/block/bdev.c >> +++ b/block/bdev.c >> @@ -821,7 +821,7 @@ struct block_device *blkdev_get_no_open(dev_t dev, bool autoload) >> struct inode *inode; >> >> inode = ilookup(blockdev_superblock, dev); >> - if (!inode && autoload && IS_ENABLED(CONFIG_BLOCK_LEGACY_AUTOLOAD)) { >> + if (0) { >> blk_request_module(dev); >> inode = ilookup(blockdev_superblock, dev); >> if (inode) >> diff --git a/block/genhd.c b/block/genhd.c >> index 9bbc38d12792..3c9116fdc1ce 100644 >> --- a/block/genhd.c >> +++ b/block/genhd.c >> @@ -428,6 +428,8 @@ static void add_disk_final(struct gendisk *disk) >> set_bit(GD_ADDED, &disk->state); >> } >> >> +#include >> + >> static int __add_disk(struct device *parent, struct gendisk *disk, >> const struct attribute_group **groups, >> struct fwnode_handle *fwnode) >> @@ -497,6 +499,9 @@ static int __add_disk(struct device *parent, struct gendisk *disk, >> if (ret) >> goto out_free_ext_minor; >> >> + if (disk->major == LOOP_MAJOR) >> + msleep(2500); // delay 2.5s for all loops >> + > > Yes, so you need to watch for the uevent to happen, THEN it is safe to > access the block device. Doing it before then isn't a good idea :) > > But, if you think this is an issue, do you have a patch that passes your > testing to fix it? I just raise it up for some ideas, and this change is buried into the code refactor and honestly I need to look into the codebase and related patchsets first. Currently I have dozens of other development stuffs on hand, if it's really a regression, I do hope Christoph or other folks who are familiar with the code could try to address this. Thanks, Gao Xiang > > thanks, > > greg k-h