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From: Waiman Long <longman@redhat.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	cgroups@vger.kernel.org, linux-mm@kvack.org
Cc: Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>,
	Vladimir Davydov <vdavydov.dev@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC PATCH 1/3] mm/memcg: Protect per-CPU counter by disabling preemption on PREEMPT_RT
Date: Wed, 22 Dec 2021 21:31:36 -0500	[thread overview]
Message-ID: <bdfc9791-4af2-f4fb-9ef5-dab1e2e3ff89@redhat.com> (raw)
In-Reply-To: <20211222114111.2206248-2-bigeasy@linutronix.de>

On 12/22/21 06:41, Sebastian Andrzej Siewior wrote:
> The per-CPU counter are modified with the non-atomic modifier. The
> consistency is ensure by disabling interrupts for the update.
> This breaks on PREEMPT_RT because some sections additionally
> acquire a spinlock_t lock (which becomes sleeping and must not be
> acquired with disabled interrupts). Another problem is that
> mem_cgroup_swapout() expects to be invoked with disabled interrupts
> because the caller has to acquire a spinlock_t which is acquired with
> disabled interrupts. Since spinlock_t never disables interrupts on
> PREEMPT_RT the interrupts are never disabled at this point.
>
> The code is never called from in_irq() context on PREEMPT_RT therefore

How do you guarantee that these percpu update functions won't be called 
in in_irq() context for PREEMPT_RT? Do you think we should add a 
WARN_ON_ONCE(in_irq()) just to be sure?

Cheers,
Longman



  reply	other threads:[~2021-12-23  2:31 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-22 11:41 [RFC PATCH 0/3] mm/memcg: Address PREEMPT_RT problems instead of disabling it Sebastian Andrzej Siewior
2021-12-22 11:41 ` [RFC PATCH 1/3] mm/memcg: Protect per-CPU counter by disabling preemption on PREEMPT_RT Sebastian Andrzej Siewior
2021-12-23  2:31   ` Waiman Long [this message]
2021-12-23  7:34     ` Sebastian Andrzej Siewior
2021-12-23 16:01       ` Waiman Long
2022-01-05 14:16   ` Michal Koutný
2022-01-13 13:08     ` Sebastian Andrzej Siewior
2022-01-13 14:48       ` Michal Koutný
2022-01-14  9:09         ` Sebastian Andrzej Siewior
2022-01-18 18:26           ` [PATCH] mm/memcg: Do not check v1 event counter when not needed Michal Koutný
2022-01-18 19:57             ` Sebastian Andrzej Siewior
2021-12-22 11:41 ` [RFC PATCH 2/3] mm/memcg: Add a local_lock_t for IRQ and TASK object Sebastian Andrzej Siewior
2021-12-23 21:38   ` Waiman Long
2022-01-03 16:34     ` Sebastian Andrzej Siewior
2022-01-03 17:09       ` Waiman Long
2021-12-22 11:41 ` [RFC PATCH 3/3] mm/memcg: Allow the task_obj optimization only on non-PREEMPTIBLE kernels Sebastian Andrzej Siewior
2021-12-23 21:48   ` Waiman Long
2022-01-03 14:44     ` Sebastian Andrzej Siewior
2022-01-03 15:04       ` Waiman Long
2022-01-05 20:22         ` Sebastian Andrzej Siewior
2022-01-06  3:28           ` Waiman Long
2022-01-13 15:26             ` Sebastian Andrzej Siewior
2022-01-05 14:59 ` [RFC PATCH 0/3] mm/memcg: Address PREEMPT_RT problems instead of disabling it Michal Koutný
2022-01-05 15:06   ` Sebastian Andrzej Siewior

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