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 D4ABCA55 for ; Sat, 7 Sep 2024 09:49:03 +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=1725702546; cv=none; b=BtHVcZGouYmkFBqwpfBoCcy18mc1zjD18CF0TUTvfkzcBlCr+Ez5h32OjG/8HJ6d5RRHliom8U6cjoGtOpZmGBIxUdAXu42yk65k098t7u0xljm6md4ZCNRqgH0uiO1Z6c4H6xHcX8izaX/UQbkJx5zhm3rT/goqvlMNhKB7PWQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725702546; c=relaxed/simple; bh=SNwsF0G0I3OJebov3MYlXjGnqLm5ExD5ovzKNpuOA/o=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=VY8A0OPxVInaJzl+yD720LYBzqY7oXdWn5rKoiHBEyN5wmiK6Jj0N+iT1wDnon1hm35P9WYrN07cCMe/Vwjv73zxTTGMox18xlcVWs1NOCbQNikQteA8fmM5A8t1W1QiT0kpYHjIiFH13YNBDxaVhTqzgxDIljwfInqmq87ya4k= 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=A8CMfxu6; 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="A8CMfxu6" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1725702542; 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=MhlT3rqK55K6OzL691fmBXNDA+C75tcbN9CuTjqVSkQ=; b=A8CMfxu6bsVek2o9oUnQgommxAlH9X1ZLgGPqtcpkAnPy8vorwXjPtvyHXNNIW+ucTshEP Wtz8/o0E0uRbOKIRXGNcDlC/Vi248Eie7U5T0UxC9wuFstB7tVimE7l+J53sncu01wGT3v cS6RtsJt7bxni8Oern65vzWRoQ6vnd8= Received: from mx-prod-mc-01.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-670-nRdlMIV8MLmw8rWspTUAoQ-1; Sat, 07 Sep 2024 05:48:59 -0400 X-MC-Unique: nRdlMIV8MLmw8rWspTUAoQ-1 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C34351956089; Sat, 7 Sep 2024 09:48:57 +0000 (UTC) Received: from fedora (unknown [10.72.116.7]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 17F721956048; Sat, 7 Sep 2024 09:48:49 +0000 (UTC) Date: Sat, 7 Sep 2024 17:48:44 +0800 From: Ming Lei To: Damien Le Moal Cc: "Richard W.M. Jones" , Jens Axboe , linux-block@vger.kernel.org, Jeff Moyer , Jiri Jaburek , Christoph Hellwig , Bart Van Assche , Hannes Reinecke , Chaitanya Kulkarni , ming.lei@redhat.com 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: <4d7280eb-7f26-4652-a1d4-4f82c4d99a4c@kernel.org> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 On Sat, Sep 07, 2024 at 06:04:59PM +0900, 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 Right, I remember that the freezing starts to cover update of max_sectors_kb. > be to do the request_module() before freezing the queue. > Something like below should work (totally untested and that may be overkill). > > diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c > index 60116d13cb80..aef87f6b4a8a 100644 > --- a/block/blk-sysfs.c > +++ b/block/blk-sysfs.c > @@ -23,6 +23,7 @@ > struct queue_sysfs_entry { > struct attribute attr; > ssize_t (*show)(struct gendisk *disk, char *page); > + int (*pre_store)(struct gendisk *disk, const char *page, size_t count); It seems over-kill to add one new callback, and another way is just to not freeze queue for storing elevator. But if other attribute update needs to not freeze queue, 'pre_store' looks one reasonable solution. diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 60116d13cb80..c418edf66f0c 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -666,15 +666,24 @@ queue_attr_store(struct kobject *kobj, struct attribute *attr, struct gendisk *disk = container_of(kobj, struct gendisk, queue_kobj); struct request_queue *q = disk->queue; ssize_t res; + bool need_freeze; if (!entry->store) return -EIO; - blk_mq_freeze_queue(q); + /* + * storing scheduler freezes queue in its way, especially + * loading scheduler module can't be done when queue is frozen + */ + need_freeze = (entry->store == elv_iosched_store); + + if (need_freeze) + blk_mq_freeze_queue(q); mutex_lock(&q->sysfs_lock); res = entry->store(disk, page, length); mutex_unlock(&q->sysfs_lock); - blk_mq_unfreeze_queue(q); + if (need_freeze) + blk_mq_unfreeze_queue(q); return res; } Thanks, Ming