linux-kernel - Re: [PATCH] mm: vmalloc: Use the vmap_area_lock to protect ne_fit_preload

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Message-ID: <20191004162041.GA30806@pc636>
Date:   Fri, 4 Oct 2019 18:20:41 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Daniel Wagner <dwagner@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>
Subject: Re: [PATCH] mm: vmalloc: Use the vmap_area_lock to protect
 ne_fit_preload_node

On Fri, Oct 04, 2019 at 05:37:28PM +0200, Sebastian Andrzej Siewior wrote:
> If you post something that is related to PREEMPT_RT please keep tglx and
> me in Cc.
> 
> On 2019-10-03 11:09:06 [+0200], Daniel Wagner wrote:
> > Replace preempt_enable() and preempt_disable() with the vmap_area_lock
> > spin_lock instead. Calling spin_lock() with preempt disabled is
> > illegal for -rt. Furthermore, enabling preemption inside the
> 
> Looking at it again, I have reasonable doubt that this
> preempt_disable() is needed.
> 
The intention was to preload a current CPU with one extra object in
non-atomic context, thus to use GFP_KERNEL permissive parameters. I.e.
that allows us to avoid any allocation(if we stay on the same CPU)
when we are in atomic context do splitting.

If we have migrate_disable/enable, then, i think preempt_enable/disable
should be replaced by it and not the way how it has been proposed
in the patch.

--
Vlad Rezki