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From: Johannes Weiner <hannes@cmpxchg.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-mm@kvack.org, Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v2] mm: workingset: replace IRQ-off check with a lockdep assert.
Date: Mon, 11 Feb 2019 13:53:18 -0500	[thread overview]
Message-ID: <20190211185318.GA13953@cmpxchg.org> (raw)
In-Reply-To: <20190211113829.sqf6bdi4c4cdd3rp@linutronix.de>

On Mon, Feb 11, 2019 at 12:38:29PM +0100, Sebastian Andrzej Siewior wrote:
> Commit
> 
>   68d48e6a2df57 ("mm: workingset: add vmstat counter for shadow nodes")
> 
> introduced an IRQ-off check to ensure that a lock is held which also
> disabled interrupts. This does not work the same way on -RT because none
> of the locks, that are held, disable interrupts.
> Replace this check with a lockdep assert which ensures that the lock is
> held.
> 
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

I'm not against checking for the lock, but if IRQs aren't disabled,
what ensures __mod_lruvec_state() is safe? I'm guessing it's because
preemption is disabled and irq handlers are punted to process context.

That said, it seems weird to me that

	spin_lock_irqsave();
	BUG_ON(!irqs_disabled());
	spin_unlock_irqrestore();

would trigger. Wouldn't it make sense to have a raw_irqs_disabled() or
something and keep the irqs_disabled() abstraction layer intact?


  reply	other threads:[~2019-02-11 18:53 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-11  9:57 [PATCH] mm: workingset: replace IRQ-off check with a lockdep assert Sebastian Andrzej Siewior
2019-02-11 11:38 ` [PATCH v2] " Sebastian Andrzej Siewior
2019-02-11 18:53   ` Johannes Weiner [this message]
2019-02-11 19:13     ` Sebastian Andrzej Siewior
2019-02-11 19:17       ` Matthew Wilcox
2019-02-11 19:41         ` Sebastian Andrzej Siewior
2019-02-11 21:02       ` Johannes Weiner
2019-02-13  9:27         ` Sebastian Andrzej Siewior
2019-02-13 14:56           ` Johannes Weiner
2019-08-21 11:21             ` Sebastian Andrzej Siewior
2019-08-21 15:21               ` Johannes Weiner
2019-02-11 17:07 ` [PATCH] " kbuild test robot
2019-02-11 17:37 ` kbuild test robot

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