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 642972D627 for ; Sat, 7 Sep 2024 07:59:17 +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=1725695959; cv=none; b=WH7TO4duyrV8ZklyXxqOmOnQeWMC4Nz4uY0Jhk+0WBH+DHc4c1zrcBl8S0SwBQGmgcE5aA91keCfIvKAksDHcpiwJ80WMSHapO+mpWKYs6oQ8ctYuwkrbS8I0dbPpkn3go2U/NaW7GYaxXKrPdzdAkHbh/YGYhf6x2r5bHF0fYw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725695959; c=relaxed/simple; bh=a9AJq1SO6RuTCIfXzD8+WsYb/Gk0mhIZZXNfg2yjfXE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=O1fa+PGNvk5w4YfyKk3sjpUuZHD0YDab9N6Ns3T/68nVVu2IhFsvFzk+yX+u2la2yP4eBNGMD5773uPQ0mbI1ykmENcVLE9/5rQPmFgwrL9d+nY0PAJaUr9w90ncJO8HLxelMliSISlgxojF2eMSpzJwUEI5EQSNbkt/PPRgofw= 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=Gc/pn7vo; 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="Gc/pn7vo" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1725695956; 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=9t+w9ZP+W/177rHsNpTimrgWEidK4mmgD4uvY1slRuw=; b=Gc/pn7voE8PYxR1J2nw4iK8pCMTEFqlsqOjOH+j7uJqBOiuSUbPBARdBauMUoVq4JHWUwV rg5seOmyCW80W+fd4uWyFoVW90jANGKsblUKdUPGn18SE2bnkvdftiN5XaVSe3+NAwz0Um 3CxJASOIma+ZF3YUJCysgdAwDTIN4gU= Received: from mx-prod-mc-03.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-356-2T1v7SizMYWW36WCgjGKzg-1; Sat, 07 Sep 2024 03:59:12 -0400 X-MC-Unique: 2T1v7SizMYWW36WCgjGKzg-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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 33AFA19560BF; Sat, 7 Sep 2024 07:59:11 +0000 (UTC) Received: from fedora (unknown [10.72.116.7]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2543319560AA; Sat, 7 Sep 2024 07:59:02 +0000 (UTC) Date: Sat, 7 Sep 2024 15:58:57 +0800 From: Ming Lei To: "Richard W.M. Jones" Cc: Jens Axboe , linux-block@vger.kernel.org, Jeff Moyer , Jiri Jaburek , Christoph Hellwig , Bart Van Assche , Damien Le Moal , 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> 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: <20240907073522.GW1450@redhat.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 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. Thanks, Ming