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Date:   Thu, 16 Apr 2020 22:56:36 +0200
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     "Paul E. McKenney" <paulmck@kernel.org>,
        Uladzislau Rezki <urezki@gmail.com>, rcu@vger.kernel.org,
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        Lai Jiangshan <jiangshanlai@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Mike Galbraith <efault@gmx.de>
Subject: Re: [PATCH 1/3] rcu: Use static initializer for krc.lock
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On 2020-04-16 14:43:48 [-0400], Joel Fernandes wrote:
> > Fair enough!  IIRC, get_page() uses non-raw spinlocks, so...
> 
> Oh, I see Paul made the same suggestion I did for raw spinlocks.
> 
> migrate_disable() is fine, but note that in the later code we will not be
> sleeping even during the get_page(), so I don't see a problem with raw
> spinlock... did I miss something?

The buddy allocator, which get_page() is using, is using spinlock_t
which is a sleeping lock. You can't have memory allocations within a
raw_spinlock_t section even with GFP_ATOMIC on PREEMPT_RT.

> thanks,
> 
>  - Joel

Sebastian