linux-kernel - Re: [PATCH 3/4] mm: Add free()

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Message-ID: <20180403114117.GA5832@bombadil.infradead.org>
Date:   Tue, 3 Apr 2018 04:41:17 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Pavel Machek <pavel@....cz>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>, linux-mm@...ck.org,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        linux-kernel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 3/4] mm: Add free()

On Tue, Apr 03, 2018 at 10:50:59AM +0200, Pavel Machek wrote:
> > gcc already does some nice optimisations around free().  For example, it
> > can eliminate dead stores:
> 
> Are we comfortable with that optimalization for kernel?
> 
> us: "Hey, let's remove those encryption keys before freeing memory."
> gcc: :-).
> 
> us: "Hey, we want to erase lock magic values not to cause confusion
> later."
> gcc: "I like confusion!"
> 
> Yes, these probably can be fixed by strategic "volatile" and/or
> barriers, but...

Exactly, we should mark those sites explicitly with volatile so that 
they aren't dead stores.