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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 56CC6C432C0 for ; Tue, 26 Nov 2019 18:29:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1F9EB2075C for ; Tue, 26 Nov 2019 18:29:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574792950; bh=/JBjShSc4phuwROTl03RtO3xe9MziFIFoNS57X41jzE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=U9adSrpRMMLowKJEZ9gIqcAXPdbUAbqOJmOT5RiMbz0NK67DiBtNzZs16EwRMlLkD /+Nt5+AdzLFHw69R/QKwBwxQm4CwUitmE0UjgY3FT5dZ2BIOMa3fIbO8I7yWnY1zwk TtuWUqmalueJcituQJROqUqOunSW5NeF4T8LARzo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725933AbfKZS3J (ORCPT ); Tue, 26 Nov 2019 13:29:09 -0500 Received: from mail.kernel.org ([198.145.29.99]:59532 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725895AbfKZS3J (ORCPT ); Tue, 26 Nov 2019 13:29:09 -0500 Received: from localhost (unknown [104.132.0.81]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 41E592073F; Tue, 26 Nov 2019 18:29:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574792948; bh=/JBjShSc4phuwROTl03RtO3xe9MziFIFoNS57X41jzE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=2Xj79GV0wyjT9K35DRi1fR5YGbkKvLegDQlK1OQiMeg8By0KsEuAPyh7jZijco78g 3BA00SMQOVDkTm8gD1gAz+V5/6KaIcS1NVqvYjGpEQMFzQrqKTZIruGbuDieG6iRQR 4GBVGFiPgq6UUoYDSHXDHppF5ZsB24VAuTkjyjrk= Date: Tue, 26 Nov 2019 10:29:07 -0800 From: Jaegeuk Kim To: Bart Van Assche Cc: Jens Axboe , linux-block@vger.kernel.org Subject: Re: [PATCH v2] loop: avoid EAGAIN, if offset or block_size are changed Message-ID: <20191126182907.GA5510@jaegeuk-macbookpro.roam.corp.google.com> References: <20190518004751.18962-1-jaegeuk@kernel.org> <20190518005304.GA19446@jaegeuk-macbookpro.roam.corp.google.com> <1e1aae74-bd6b-dddb-0c88-660aac33872c@acm.org> <20191125175913.GC71634@jaegeuk-macbookpro.roam.corp.google.com> <20191125192251.GA76721@jaegeuk-macbookpro.roam.corp.google.com> <4ab43c9d-8b95-7265-2b55-b6d526938b32@acm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4ab43c9d-8b95-7265-2b55-b6d526938b32@acm.org> User-Agent: Mutt/1.8.2 (2017-04-18) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 11/25, Bart Van Assche wrote: > On 11/25/19 11:41 AM, Bart Van Assche wrote: > > On 11/25/19 11:22 AM, Jaegeuk Kim wrote: > > > On 11/25, Bart Van Assche wrote: > > > > Thank you for the additional and very helpful clarification. Can > > > > you have a look at the (totally untested) patch below? I prefer > > > > that version because it prevents concurrent processing of > > > > requests and syncing/killing the bdev. > > > > > > Yeah, I thought this was much cleaner way, but wasn't sure it could > > > be doable > > > to sync|kill block device after freezing the queue. Is it okay? > > > > Hi Jaegeuk, > > > > That patch was based on an incorrect interpretation of the meaning of > > lo_device. After having taken another loop at the block driver, I don't > > think that calling sync after freezing the queue is OK. How about using > > the following call sequence: > > * sync_blockdev() > > * blk_mq_freeze_queue() > > * kill_bdev() > > This is what I had in mind (still untested): > > > Subject: [PATCH] loop: Avoid EAGAIN if the offset or the block_size are changed > > After sync_blockdev() has been called, more requests can be submitted > to the loop device. These requests dirty additional pages, causing > loop_set_status() to return -EAGAIN. Not all user space code that > changes the offset and/or the block size handles -EAGAIN correctly. > Hence make sure that loop_set_status() does not return -EAGAIN. > > Cc: Jaegeuk Kim > Cc: Gwendal Grignou > Cc: grygorii tertychnyi > Cc: Andrew Norrie > Cc: > Fixes: 5db470e229e2 ("loop: drop caches if offset or block_size are changed") > Reported-by: Gwendal Grignou > Reported-by: grygorii tertychnyi > Reported-by: Jaegeuk Kim > Signed-off-by: Bart Van Assche > --- > drivers/block/loop.c | 56 ++++++++++++++++++-------------------------- > 1 file changed, 23 insertions(+), 33 deletions(-) > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index 739b372a5112..84bdb3a6f6d0 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -1264,14 +1264,17 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info) > goto out_unlock; > } > > - if (lo->lo_offset != info->lo_offset || > - lo->lo_sizelimit != info->lo_sizelimit) { > - sync_blockdev(lo->lo_device); > - kill_bdev(lo->lo_device); > - } > + /* > + * Drain the page cache and the request queue. Set the "dying" flag to > + * prevent that kill_bdev() locks up. > + */ > + sync_blockdev(lo->lo_device); > > - /* I/O need to be drained during transfer transition */ > - blk_mq_freeze_queue(lo->lo_queue); > + blk_set_queue_dying(lo->lo_queue); > + blk_mq_freeze_queue_wait(lo->lo_queue); > + > + /* Kill buffers that got dirtied after the sync_blockdev() call. */ Any race condition where we can truncate any dirty pages written between sync_blockdev() and kill_bdev()? Thanks, > + kill_bdev(lo->lo_device); > > err = loop_release_xfer(lo); > if (err) > @@ -1298,14 +1301,6 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info) > > if (lo->lo_offset != info->lo_offset || > lo->lo_sizelimit != info->lo_sizelimit) { > - /* kill_bdev should have truncated all the pages */ > - if (lo->lo_device->bd_inode->i_mapping->nrpages) { > - err = -EAGAIN; > - pr_warn("%s: loop%d (%s) has still dirty pages (nrpages=%lu)\n", > - __func__, lo->lo_number, lo->lo_file_name, > - lo->lo_device->bd_inode->i_mapping->nrpages); > - goto out_unfreeze; > - } > if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit)) { > err = -EFBIG; > goto out_unfreeze; > @@ -1341,6 +1336,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info) > __loop_update_dio(lo, lo->use_dio); > > out_unfreeze: > + blk_queue_flag_clear(QUEUE_FLAG_DYING, lo->lo_queue); > blk_mq_unfreeze_queue(lo->lo_queue); > > if (!err && (info->lo_flags & LO_FLAGS_PARTSCAN) && > @@ -1531,39 +1527,33 @@ static int loop_set_dio(struct loop_device *lo, unsigned long arg) > > static int loop_set_block_size(struct loop_device *lo, unsigned long arg) > { > - int err = 0; > - > if (lo->lo_state != Lo_bound) > return -ENXIO; > > if (arg < 512 || arg > PAGE_SIZE || !is_power_of_2(arg)) > return -EINVAL; > > - if (lo->lo_queue->limits.logical_block_size != arg) { > - sync_blockdev(lo->lo_device); > - kill_bdev(lo->lo_device); > - } > + /* > + * Drain the page cache and the request queue. Set the "dying" flag to > + * prevent that kill_bdev() locks up. > + */ > + sync_blockdev(lo->lo_device); > > - blk_mq_freeze_queue(lo->lo_queue); > + blk_set_queue_dying(lo->lo_queue); > + blk_mq_freeze_queue_wait(lo->lo_queue); > > - /* kill_bdev should have truncated all the pages */ > - if (lo->lo_queue->limits.logical_block_size != arg && > - lo->lo_device->bd_inode->i_mapping->nrpages) { > - err = -EAGAIN; > - pr_warn("%s: loop%d (%s) has still dirty pages (nrpages=%lu)\n", > - __func__, lo->lo_number, lo->lo_file_name, > - lo->lo_device->bd_inode->i_mapping->nrpages); > - goto out_unfreeze; > - } > + /* Kill buffers that got dirtied after the sync_blockdev() call. */ > + kill_bdev(lo->lo_device); > > blk_queue_logical_block_size(lo->lo_queue, arg); > blk_queue_physical_block_size(lo->lo_queue, arg); > blk_queue_io_min(lo->lo_queue, arg); > loop_update_dio(lo); > -out_unfreeze: > + > + blk_queue_flag_clear(QUEUE_FLAG_DYING, lo->lo_queue); > blk_mq_unfreeze_queue(lo->lo_queue); > > - return err; > + return 0; > } > > static int lo_simple_ioctl(struct loop_device *lo, unsigned int cmd,