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Date: Tue, 17 Sep 2024 07:53:31 +0200
From: Christoph Hellwig <hch@lst.de>
To: Damien Le Moal <dlemoal@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
	"Richard W . M . Jones" <rjones@redhat.com>,
	Ming Lei <ming.lei@redhat.com>, Jeff Moyer <jmoyer@redhat.com>,
	Jiri Jaburek <jjaburek@redhat.com>, Christoph Hellwig <hch@lst.de>,
	Bart Van Assche <bvanassche@acm.org>,
	Hannes Reinecke <hare@suse.de>, Chaitanya Kulkarni <kch@nvidia.com>,
	Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Subject: Re: [PATCH] block: Fix elv_iosched_local_module handling of "none"
 scheduler
Message-ID: <20240917055331.GA2432@lst.de>
References: <20240917053258.128827-1-dlemoal@kernel.org>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Tue, Sep 17, 2024 at 02:32:58PM +0900, Damien Le Moal wrote:
> Commit 734e1a860312 ("block: Prevent deadlocks when switching
> elevators") introduced the function elv_iosched_load_module() to allow
> loading an elevator module outside of elv_iosched_store() with the
> target device queue not frozen, to avoid deadlocks. However, the "none"
> scheduler does not have a module and as a result,
> elv_iosched_load_module() always returns an error when trying to switch
> to this valid scheduler.
> 
> Fix this by checking that the requested scheduler is "none" and doing
> nothing in that case.

The old code before this commit simply ignored the request_module,
just as most callers of it do.  I think that's the right approach
here as well.