From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Shakeel Butt <shakeel.butt@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Muchun Song <muchun.song@linux.dev>,
Yosry Ahmed <yosry.ahmed@linux.dev>,
Waiman Long <llong@redhat.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org,
Meta kernel team <kernel-team@meta.com>
Subject: Re: [PATCH] memcg: decouple memcg_hotplug_cpu_dead from stock_lock
Date: Fri, 11 Apr 2025 16:06:46 +0200 [thread overview]
Message-ID: <20250411140646.05s0O5SY@linutronix.de> (raw)
In-Reply-To: <0e9e2d5d-ec64-4ad4-a184-0c53832ff565@suse.cz>
On 2025-04-11 10:55:31 [+0200], Vlastimil Babka wrote:
> > @@ -1964,10 +1964,10 @@ static int memcg_hotplug_cpu_dead(unsigned int cpu)
> >
> > stock = &per_cpu(memcg_stock, cpu);
> >
> > - /* drain_obj_stock requires stock_lock */
> > - local_lock_irqsave(&memcg_stock.stock_lock, flags);
> > - drain_obj_stock(stock);
> > - local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
> > + local_irq_save(flag);
>
> I think for RT this is not great? At least in theory, probably it's not
> actually used together with cpu hotplug? As it relies on memcg_stats_lock()
> I think no irq save/enable is necessary there. local_lock_irqsave wasn't
> actually a irq disable on RT. I don't know if there's a handy wrapper for this.
No seeing the whole context but memcg_hotplug_cpu_dead() should be
invoked the control CPU while "cpu" is already gone. So the local_lock
should be acquired and the target CPU needs no locks since it is
offline. local_irq_save() will break things.
Sebastian
next prev parent reply other threads:[~2025-04-11 14:06 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-10 21:06 Shakeel Butt
2025-04-11 0:00 ` Roman Gushchin
2025-04-11 5:06 ` Andrew Morton
2025-04-14 17:52 ` Shakeel Butt
2025-04-11 8:55 ` Vlastimil Babka
2025-04-11 14:06 ` Sebastian Andrzej Siewior [this message]
2025-04-11 17:54 ` Shakeel Butt
2025-04-11 18:06 ` Vlastimil Babka
2025-04-11 18:12 ` Shakeel Butt
2025-04-14 17:55 ` Shakeel Butt
2025-04-15 6:30 ` Sebastian Andrzej Siewior
2025-04-15 17:01 ` Shakeel Butt
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