linux-kernel - Re: [PATCH v2] memcg: Remove the lockdep assert from __mod_objcg

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Date: Tue, 28 May 2024 09:20:56 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: "Vlastimil Babka (SUSE)" <vbabka@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Hocko <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Muchun Song <muchun.song@...ux.dev>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] memcg: Remove the lockdep assert from
 __mod_objcg_mlstate().

On Tue, May 28, 2024 at 05:08:56PM GMT, Sebastian Andrzej Siewior wrote:
> On 2024-05-28 07:59:57 [-0700], Shakeel Butt wrote:
> > One question on VM_WARN_ON_IRQS_ENABLED() in __mod_memcg_lruvec_state().
> > On a PREEMPT_RT kernel with CONFIG_DEBUG_VM, will that
> > VM_WARN_ON_IRQS_ENABLED() cause a splat or VM_WARN_ON_IRQS_ENABLED is
> > special on PREEMPT_RT kernels?
> 
> we have the following in the header file:
> 
> | #ifdef CONFIG_DEBUG_VM_IRQSOFF
> | #define VM_WARN_ON_IRQS_ENABLED() WARN_ON_ONCE(!irqs_disabled())
> | #else
> | #define VM_WARN_ON_IRQS_ENABLED() do { } while (0)
> | #endif
> 
> and this in Kconfig:
> | config DEBUG_VM_IRQSOFF
> |         def_bool DEBUG_VM && !PREEMPT_RT
> |
> 
> which means on PREEMPT_RT we end up with "do {…"

Thanks for the explanation.