From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 6E09A17999 for ; Mon, 9 Sep 2024 01:25:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725845118; cv=none; b=epn/1cigsQDqvH2V5UIUgmEsgm1z+rikBzNqLN5baLYO3+0lJEbASgrEGfs4Z0futMAS0gm4hZR+7LXv/2Him30szVgqQCa6epdOUwszZiKRfQhNo4EKkqjnhg2RgDK8JOgXhiENzmfowTBUh5nNdnSYnIEGJpya9TaPIViciN0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725845118; c=relaxed/simple; bh=cnMLX1PZIWy291Sx8cqAhW0XGfFmFDjyKUfeMZicaGw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=hw/43bURqwvKSOZOILVWdG/qRiRVisIM9UN0TjjYPctTizVoRj31vXDdOHWJOX0mUpWuwFmomycnij270250qfJMMCS69HBg9Wv5dikAtyeazUgmuB6oBYk8stVjX6Gr3i2p+l3bTLhAo+99TElh+mrSpz3TuhSOv+jyA6nx6xY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Qzz/T4m0; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Qzz/T4m0" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1725845115; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=TWEupgvvQQLWwChF11q57v4KE5ViSvmDAEl87QUms50=; b=Qzz/T4m094p1Mwu9Id5/he/rg8HWQfQuMrVLTYVTIKcOqmMxn0w38IKCUt6tKly2SMjWCn ztkfB4vmd2eHtaJACEwnGMi1cvLkAxNgHPGpU/iECSYNi3NeUlZbSKCXehwPltz5FmCgzT Dzll46kUtGw4SVdlMIhYan6+6MjGXDs= Received: from mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-318--s-VMgZAO_u__uhZjd5vBA-1; Sun, 08 Sep 2024 21:25:12 -0400 X-MC-Unique: -s-VMgZAO_u__uhZjd5vBA-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id DA1321956096; Mon, 9 Sep 2024 01:25:09 +0000 (UTC) Received: from fedora (unknown [10.72.116.72]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 967C719560AA; Mon, 9 Sep 2024 01:25:01 +0000 (UTC) Date: Mon, 9 Sep 2024 09:24:56 +0800 From: Ming Lei To: Jens Axboe Cc: Damien Le Moal , "Richard W.M. Jones" , linux-block@vger.kernel.org, Jeff Moyer , Jiri Jaburek , Christoph Hellwig , Bart Van Assche , Hannes Reinecke , Chaitanya Kulkarni Subject: Re: [PATCH] block: elevator: avoid to load iosched module from this disk Message-ID: References: <20240907014331.176152-1-ming.lei@redhat.com> <20240907073522.GW1450@redhat.com> <4d7280eb-7f26-4652-a1d4-4f82c4d99a4c@kernel.org> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On Sat, Sep 07, 2024 at 07:50:32AM -0600, Jens Axboe wrote: > On 9/7/24 3:04 AM, Damien Le Moal wrote: > > On 9/7/24 16:58, Ming Lei wrote: > >> On Sat, Sep 07, 2024 at 08:35:22AM +0100, Richard W.M. Jones wrote: > >>> On Sat, Sep 07, 2024 at 09:43:31AM +0800, Ming Lei wrote: > >>>> When switching io scheduler via sysfs, 'request_module' may be called > >>>> if the specified scheduler doesn't exist. > >>>> > >>>> This was has deadlock risk because the module may be stored on FS behind > >>>> our disk since request queue is frozen before switching its elevator. > >>>> > >>>> Fix it by returning -EDEADLK in case that the disk is claimed, which > >>>> can be thought as one signal that the disk is mounted. > >>>> > >>>> Some distributions(Fedora) simulates the original kernel command line of > >>>> 'elevator=foo' via 'echo foo > /sys/block/$DISK/queue/scheduler', and boot > >>>> hang is triggered. > >>>> > >>>> Cc: Richard Jones > >>>> Cc: Jeff Moyer > >>>> Cc: Jiri Jaburek > >>>> Signed-off-by: Ming Lei > >>> > >>> I'd suggest also: > >>> > >>> Bug: https://bugzilla.kernel.org/show_bug.cgi?id=219166 > >>> Reported-by: Richard W.M. Jones > >>> Reported-by: Jiri Jaburek > >>> Tested-by: Richard W.M. Jones > >>> > >>> So I have tested this patch and it does fix the issue, at the possible > >>> cost that now setting the scheduler can fail: > >>> > >>> + for f in /sys/block/{h,s,ub,v}d*/queue/scheduler > >>> + echo noop > >>> /init: line 109: echo: write error: Resource deadlock avoided > >>> > >>> (I know I'm setting it to an impossible value here, but this could > >>> also happen when setting it to a valid one.) > >> > >> Actually in most of dist, io-schedulers are built-in, so request_module > >> is just a nop, but meta IO must be started. > >> > >>> > >>> Since almost no one checks the result of 'echo foo > /sys/...' that > >>> would probably mean that sometimes a desired setting is silently not > >>> set. > >> > >> As I mentioned, io-schedulers are built-in for most of dist, so > >> request_module isn't called in case of one valid io-sched. > >> > >>> > >>> Also I bisected this bug yesterday and found it was caused by (or, > >>> more likely, exposed by): > >>> > >>> commit af2814149883e2c1851866ea2afcd8eadc040f79 > >>> Author: Christoph Hellwig > >>> Date: Mon Jun 17 08:04:38 2024 +0200 > >>> > >>> block: freeze the queue in queue_attr_store > >>> > >>> queue_attr_store updates attributes used to control generating I/O, and > >>> can cause malformed bios if changed with I/O in flight. Freeze the queue > >>> in common code instead of adding it to almost every attribute. > >>> > >>> Reverting this commit on top of git head also fixes the problem. > >>> > >>> Why did this commit expose the problem? > >> > >> That is really the 1st bad commit which moves queue freezing before > >> calling request_module(), originally we won't freeze queue until > >> we have to do it. > >> > >> Another candidate fix is to revert it, or at least not do it > >> for storing elevator attribute. > > > > I do not think that reverting is acceptable. Rather, a proper fix would simply > > be to do the request_module() before freezing the queue. > > Something like below should work (totally untested and that may be overkill). > > I like this approach, but let's please call it something descriptive > like "load_module" or something like that. But 'load_module' is too specific as interface, and we just only have one case which need to load module exactly. I guess there may be same risk in queue_wb_lat_store() which calls into GFP_KERNEL allocation which implies direct reclaim & IO. Thanks, Ming