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=-6.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 0445FC2BA19 for ; Tue, 14 Apr 2020 15:47:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id BB67A206A2 for ; Tue, 14 Apr 2020 15:47:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="fhELgt4F" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BB67A206A2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 548378E002B; Tue, 14 Apr 2020 11:47:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4F83E8E0007; Tue, 14 Apr 2020 11:47:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 40D2F8E002B; Tue, 14 Apr 2020 11:47:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0158.hostedemail.com [216.40.44.158]) by kanga.kvack.org (Postfix) with ESMTP id 2681A8E0007 for ; Tue, 14 Apr 2020 11:47:44 -0400 (EDT) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id DC85B180AD807 for ; Tue, 14 Apr 2020 15:47:43 +0000 (UTC) X-FDA: 76706890806.30.field23_265235f1fe339 X-HE-Tag: field23_265235f1fe339 X-Filterd-Recvd-Size: 6372 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf50.hostedemail.com (Postfix) with ESMTP for ; Tue, 14 Apr 2020 15:47:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=gaNCciS1ZGObUgDnpsOAZP6AUC2c3uZoCdo1HUWts4c=; b=fhELgt4Fu4afzRcTGwnL1xPM5P DL/fB9skhUKTXHo7L0rXtnJJ3BHW88ia7IF+Qcl0FZOY81VT9DNxnqrpJkxH5Zn9+fLnU+2OJbZ3H R1GUYoKpMBmph2Iy22aWAPC7cETZpt3NhLARKn5j6QDULr2xUWxaHn2ixo9oXWa4cx7Z3nGtLMWKb iajZ1Iy+5ej/MFbgpKLXS1Bvz6IzCw9dwyw/9QTRsDxL0JUR9USuCXtRHkiwKSFY4iSDnBif88s4c uKVFWfc+ytLkNvqfq1H2oCOv35cFP3OiiDCigYwXgTFSX4HHxz6bEOEHyOHhesC5zhvY2AY6CaKkN Hwlj4epw==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jONmX-0004QS-4h; Tue, 14 Apr 2020 15:47:25 +0000 Date: Tue, 14 Apr 2020 08:47:25 -0700 From: Christoph Hellwig To: Luis Chamberlain Cc: axboe@kernel.dk, viro@zeniv.linux.org.uk, bvanassche@acm.org, gregkh@linuxfoundation.org, rostedt@goodmis.org, mingo@redhat.com, jack@suse.cz, ming.lei@redhat.com, nstange@suse.de, akpm@linux-foundation.org, mhocko@suse.com, yukuai3@huawei.com, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Omar Sandoval , Hannes Reinecke , Michal Hocko Subject: Re: [PATCH 5/5] block: revert back to synchronous request_queue removal Message-ID: <20200414154725.GD25765@infradead.org> References: <20200414041902.16769-1-mcgrof@kernel.org> <20200414041902.16769-6-mcgrof@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200414041902.16769-6-mcgrof@kernel.org> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Apr 14, 2020 at 04:19:02AM +0000, Luis Chamberlain wrote: > Commit dc9edc44de6c ("block: Fix a blk_exit_rl() regression") merged on > v4.12 moved the work behind blk_release_queue() into a workqueue after a > splat floated around which indicated some work on blk_release_queue() > could sleep in blk_exit_rl(). This splat would be possible when a driver > called blk_put_queue() or blk_cleanup_queue() (which calls blk_put_queue() > as its final call) from an atomic context. > > blk_put_queue() decrements the refcount for the request_queue > kobject, and upon reaching 0 blk_release_queue() is called. Although > blk_exit_rl() is now removed through commit db6d9952356 ("block: remove > request_list code"), we reserve the right to be able to sleep within > blk_release_queue() context. If you see no other way and *have* be > in atomic context when you driver calls the last blk_put_queue() > you can always just increase your block device's reference count with > bdgrab() as this can be done in atomic context and the request_queue > removal would be left to upper layers later. We document this bit of > tribal knowledge as well now, and adjust kdoc format a bit. > > We revert back to synchronous request_queue removal because asynchronous > removal creates a regression with expected userspace interaction with > several drivers. An example is when removing the loopback driver and > issues ioctl from userspace to do so, upon return and if successful one > expects the device to be removed. Moving to asynchronous request_queue > removal could have broken many scripts which relied on the removal to > have been completed if there was no error. > > Using asynchronous request_queue removal however has helped us find > other bugs, in the future we can test what could break with this > arrangement by enabling CONFIG_DEBUG_KOBJECT_RELEASE. > > Cc: Bart Van Assche > Cc: Omar Sandoval > Cc: Hannes Reinecke > Cc: Nicolai Stange > Cc: Greg Kroah-Hartman > Cc: Michal Hocko > Cc: yu kuai > Suggested-by: Nicolai Stange > Fixes: dc9edc44de6c ("block: Fix a blk_exit_rl() regression") > Signed-off-by: Luis Chamberlain > --- > block/blk-core.c | 19 ++++++++++++++++++- > block/blk-sysfs.c | 38 +++++++++++++++++--------------------- > include/linux/blkdev.h | 2 -- > 3 files changed, 35 insertions(+), 24 deletions(-) > > diff --git a/block/blk-core.c b/block/blk-core.c > index 5aaae7a1b338..8346c7c59ee6 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -301,6 +301,17 @@ void blk_clear_pm_only(struct request_queue *q) > } > EXPORT_SYMBOL_GPL(blk_clear_pm_only); > > +/** > + * blk_put_queue - decrement the request_queue refcount > + * > + * Decrements the refcount to the request_queue kobject, when this reaches > + * 0 we'll have blk_release_queue() called. You should avoid calling > + * this function in atomic context but if you really have to ensure you > + * first refcount the block device with bdgrab() / bdput() so that the > + * last decrement happens in blk_cleanup_queue(). > + * > + * @q: the request_queue structure to decrement the refcount for > + */ > void blk_put_queue(struct request_queue *q) > { > kobject_put(&q->kobj); > @@ -328,10 +339,16 @@ EXPORT_SYMBOL_GPL(blk_set_queue_dying); > > /** > * blk_cleanup_queue - shutdown a request queue > - * @q: request queue to shutdown > * > * Mark @q DYING, drain all pending requests, mark @q DEAD, destroy and > * put it. All future requests will be failed immediately with -ENODEV. > + * > + * You should not call this function in atomic context. If you need to > + * refcount a request_queue in atomic context, instead refcount the > + * block device with bdgrab() / bdput(). I think this needs a WARN_ON thrown in to enforece the calling context. > + * > + * @q: request queue to shutdown Moving the argument documentation seems against the usual kerneldoc style. Otherwise this look good, I hope it sticks :)