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Date: Wed, 29 May 2024 11:16:56 +0200
From: Michal Hocko <mhocko@suse.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: "Vlastimil Babka (SUSE)" <vbabka@kernel.org>,
	Shakeel Butt <shakeel.butt@linux.dev>,
	Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Muchun Song <muchun.song@linux.dev>, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v2] memcg: Remove the lockdep assert from
 __mod_objcg_mlstate().
Message-ID: <ZlbyiMnd4x24bR8F@tiehlicka>
References: <20240528121928.i-Gu7Jvg@linutronix.de>
 <09e085bb-f09e-4901-a2dd-a0b789bb8a4d@kernel.org>
 <20240528134027.OxDASsS3@linutronix.de>
 <c84d6962-34fa-42e5-899c-925579cbfb26@kernel.org>
 <20240528141341.rz_rytN_@linutronix.de>
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On Tue 28-05-24 16:13:41, Sebastian Andrzej Siewior wrote:
> The assert was introduced in the commit cited below as an insurance that
> the semantic is the same after the local_irq_save() has been removed and
> the function has been made static.
> 
> The original requirement to disable interrupt was due the modification
> of per-CPU counters which require interrupts to be disabled because the
> counter update operation is not atomic and some of the counters are
> updated from interrupt context.
> 
> All callers of __mod_objcg_mlstate() acquire a lock
> (memcg_stock.stock_lock) which disables interrupts on !PREEMPT_RT and
> the lockdep assert is satisfied. On PREEMPT_RT the interrupts are not
> disabled and the assert triggers.
> 
> The safety of the counter update is already ensured by
> VM_WARN_ON_IRQS_ENABLED() which is part of __mod_memcg_lruvec_state() and
> does not require yet another check.
> 
> Remove the lockdep assert from __mod_objcg_mlstate().
> 
> Fixes: 91882c1617c15 ("memcg: simple cleanup of stats update functions")
> Link: https://lore.kernel.org/r/20240528121928.i-Gu7Jvg@linutronix.de
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Acked-by: Michal Hocko <mhocko@suse.com>

-- 
Michal Hocko
SUSE Labs