linux-kernel - Re: [PATCH 1/2] kernfs: add kernfs_ops.free operation to free resources tied to the file

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Date:   Tue, 27 Jun 2023 10:24:15 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Suren Baghdasaryan <surenb@...gle.com>, gregkh@...uxfoundation.org,
        peterz@...radead.org, lujialin4@...wei.com,
        lizefan.x@...edance.com, hannes@...xchg.org, mingo@...hat.com,
        ebiggers@...nel.org, oleg@...hat.com, akpm@...ux-foundation.org,
        viro@...iv.linux.org.uk, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 1/2] kernfs: add kernfs_ops.free operation to free
 resources tied to the file

On Mon, Jun 26, 2023 at 10:31:49AM -1000, Tejun Heo wrote:
> On Mon, Jun 26, 2023 at 01:17:12PM -0700, Suren Baghdasaryan wrote:
> > diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
> > index 73f5c120def8..a7e404ff31bb 100644
> > --- a/include/linux/kernfs.h
> > +++ b/include/linux/kernfs.h
> > @@ -273,6 +273,11 @@ struct kernfs_ops {
> >  	 */
> >  	int (*open)(struct kernfs_open_file *of);
> >  	void (*release)(struct kernfs_open_file *of);
> > +	/*
> > +	 * Free resources tied to the lifecycle of the file, like a
> > +	 * waitqueue used for polling.
> > +	 */
> > +	void (*free)(struct kernfs_open_file *of);
> 
> I think this can use a bit more commenting - ie. explain that release may be
> called earlier than the actual freeing of the file and how that can lead to
> problems. Othre than that, looks fine to me.

It seems the more natural thing to do would be to introduce a ->drain()
operation and order it before ->release(), no?