linux-kernel - Re: Raw spinlocks and memory allocation

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Message-ID: <20200731223016.GT9247@paulmck-ThinkPad-P72>
Date:   Fri, 31 Jul 2020 15:30:16 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Matthew Wilcox <willy@...radead.org>, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        hannes@...xchg.org, urezki@...il.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: Raw spinlocks and memory allocation

On Fri, Jul 31, 2020 at 02:29:19PM -0700, Andrew Morton wrote:
> On Fri, 31 Jul 2020 14:24:57 -0700 "Paul E. McKenney" <paulmck@...nel.org> wrote:
> 
> > The reason for this restriction is that in -rt, the spin_lock(&zone->lock)
> > in rmqueue_bulk() can sleep.
> 
> So if there is runtime overhead, this overhead could be restricted to
> -rt kernels with suitable ifdefs?

In theory, yes.  In practice, with CONFIG_PROVE_RAW_LOCK_NESTING=y,
lockdep will complain regardless of -rt or not.

							Thanx, Paul