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From:   SeongJae Park <sj38.park@gmail.com>
To:     Jonathan Cameron <Jonathan.Cameron@Huawei.com>
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Subject: Re: Re: [PATCH v6 02/14] mm/damon: Implement region based sampling
Date:   Fri, 13 Mar 2020 21:16:49 +0100
Message-Id: <20200313201649.26646-1-sj38.park@gmail.com>
In-Reply-To: <20200313172954.00001f3c@Huawei.com> (raw)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, 13 Mar 2020 17:29:54 +0000 Jonathan Cameron <Jonathan.Cameron@Huawei.com> wrote:

> On Mon, 24 Feb 2020 13:30:35 +0100
> SeongJae Park <sjpark@amazon.com> wrote:
> 
> > From: SeongJae Park <sjpark@amazon.de>
> > 
> > This commit implements DAMON's basic access check and region based
> > sampling mechanisms.  This change would seems make no sense, mainly
> > because it is only a part of the DAMON's logics.  Following two commits
> > will make more sense.
> > 
[...]
> 
> Came across a minor issue inline.  kthread_run calls kthread_create.
> That gives a potential sleep while atomic issue given the spin lock.
> 
> Can probably be fixed by preallocating the thread then starting it later.
> 
> Jonathan
[...]
> > +/*
> > + * Start or stop the kdamond
> > + *
> > + * Returns 0 if success, negative error code otherwise.
> > + */
> > +static int damon_turn_kdamond(struct damon_ctx *ctx, bool on)
> > +{
> > +	spin_lock(&ctx->kdamond_lock);
> > +	ctx->kdamond_stop = !on;
> > +	if (!ctx->kdamond && on) {
> > +		ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond");
> 
> Can't do this under a spin lock.

Good catch!  And, agree to your suggestion.  I will fix this in that way!


Thanks,
SeongJae Park